Development of a food frequency questionnaire module and databases for compounds in cooked and processed meats

Integrating Microbiome Analysis, Metabolomics, Bioinformatics, and Histopathology to Elucidate the Protective Effects of Pomegranate Juice against Benzo-alpha-pyrene-Induced Colon Pathologies

Polycyclic aromatic hydrocarbons, e.g., benzo[a]pyrene (BaP), are common dietary pollutants with potential carcinogenic activity, while polyphenols are potential chemopreventive antioxidants. Although several health benefits are attributed to polyphenol-rich pomegranate, little is known about its interaction with BaP. This study integrates histochemical, microbiomic, and metabolomic approaches to investigate the protective effects of pomegranate juice from BaP-induced pathologies. To this end, 48 Sprague-Dawley rats received, for four weeks, either pomegranate, BaP, both, or neither (n = 12 rats per group). Whereas histochemical examination of the colon indicated tissue damage marked by mucin depletion in BaP-fed animals, which was partially restored by administration of pomegranate juice, the fecal microbiome and metabolome retained their resilience, except for key changes related to pomegranate and BaP biotransformation. Meanwhile, dramatic microbiome restructuring and metabolome shift were observed as a consequence of the elapsed time (age factor). Additionally, the analysis allowed a thorough examination of fecal microbiome-metabolome associations, which delineated six microbiome clusters (marked by a differential abundance of Lactobacillaceae and Prevotellaceae, Rumincococcaceae, and Erysipelotrichaceae) and two major metabolome clusters (a sugar- and amino-acids-dominated metabotype vs. a cluster of fatty acids and hydrocarbons), with sugar alcohols maintaining a unique signature. In conclusion, using paired comparisons to minimize inter-individual animal variations allowed the dissection of temporal vs. treatment-derived variations. Microbiome-metabolome association clusters may be further exploited for metabotype prediction and gut-health biomarker discovery.

The Cooked Meat Carcinogen 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine Hair Dosimeter, DNA Adductomics Discovery, and Associations with Prostate Cancer Pathology Biomarkers

Well-done cooked red meat consumption is linked to aggressive prostate cancer (PC) risk. Identifying mutation-inducing DNA adducts in the prostate genome can advance our understanding of chemicals in meat that may contribute to PC. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a heterocyclic aromatic amine (HAA) formed in cooked meat, is a potential human prostate carcinogen. PhIP was measured in the hair of PC patients undergoing prostatectomy, bladder cancer patients under treatment for cystoprostatectomy, and patients treated for benign prostatic hyperplasia (BPH). PhIP hair levels were above the quantification limit in 123 of 205 subjects. When dichotomizing prostate pathology biomarkers, the geometric mean PhIP hair levels were higher in patients with intermediate and elevated-risk prostate-specific antigen values than lower-risk values <4 ng/mL (p = 0.03). PhIP hair levels were also higher in patients with intermediate and high-risk Gleason scores ≥7 compared to lower-risk Gleason score 6 and BPH patients (p = 0.02). PC patients undergoing prostatectomy had higher PhIP hair levels than cystoprostatectomy or BPH patients (p = 0.02). PhIP-DNA adducts were detected in 9.4% of the patients assayed; however, DNA adducts of other carcinogenic HAAs, and benzo[a]pyrene formed in cooked meat, were not detected. Prostate specimens were also screened for 10 oxidative stress-associated lipid peroxidation (LPO) DNA adducts. Acrolein 1,N²-propano-2'-deoxyguanosine adducts were detected in 54.5% of the patients; other LPO adducts were infrequently detected. Acrolein adducts were not associated with prostate pathology biomarkers, although DNA adductomic profiles differed between PC patients with low and high-grade Gleason scores. Many DNA adducts are of unknown origin; however, dG adducts of formaldehyde and a series of purported 4-hydroxy-2-alkenals were detected at higher abundance in a subset of patients with elevated Gleason scores. The PhIP hair biomarker and DNA adductomics data support the paradigm of well-done cooked meat and oxidative stress in aggressive PC risk.

Heterogeneity in Meat Food Groups Can Meaningfully Alter Population-Level Intake Estimates of Red Meat and Poultry

Heterogeneity in meat food groups hinders interpretation of research regarding meat intake and chronic disease risk. Our objective was to investigate how heterogeneity in red meat (RM) and poultry food groups influences US population intake estimates. Based on a prior systematic review, we created an ontology of methods used to estimate RM [1= unprocessed RM; 2 (reference)= unprocessed RM + processed RM; 3= unprocessed RM + processed RM + processed poultry; and 4=unprocessed RM + processed RM + processed poultry + chicken patties/nuggets/tenders (PNT)] and three for poultry [A=unprocessed poultry; B= unprocessed poultry + PNT; C (reference)= unprocessed poultry + processed poultry + PNT). We applied methods to 2015-18 National Health and Nutrition Examination Survey data to estimate RM and poultry intake prevalence and amount. We estimated and compared intakes within RM and within poultry methods via the NCI Method for individuals ≥2 years old (n = 15,038), adjusted for age, sex, and race/Hispanic origin. We compared the population percentage that exceeded age- and sex-specific RM and poultry allotments from the Dietary Guidelines for Americans recommended eating patterns. The percent that consumed RM ranged from 47 ± 1.2% to 75 ± 0.8% across methods and mean amount ranged from 10.5 ± 0.28 to 18.2 ± 0.35 lean oz-equivalents/week; 38 ± 1.2% to 71 ± 0.7% and 9.8 ± 0.35 to 13.3 ± 0.35 lean oz-equivalents/week across poultry methods. Estimates for higher, but not lower, intake percentiles differed across RM methods. Compared to the reference, Method 1 was ≥3.0 oz-equivalents/week lower from 20th-70th percentiles, ≥6.0 oz-equivalents/week lower from 75th-90th percentiles, and ≥9.0 oz-equivalents/week lower for the 95th percentile. Method 4, but not Method 3, was ≥3.0 oz-equivalents/week higher than the reference from 50 to 95th percentiles. The population percentage that exceeded allotments was 27 ± 1.8% lower for Method 1, 9 ± 0.8% higher for Method 3, and 14 ± 0.9% higher for Method 4 compared to the reference. Differences were less pronounced for poultry. Our analysis quantifies the magnitude of bias introduced by heterogeneous meat food group methodology. Explicit descriptions of meat food groups are important for development of dietary recommendations to ensure that research studies are compared appropriately.

Dietary heterocyclic aromatic amine intake and cancer risk: epidemiological evidence from Japanese studies

Heterocyclic aromatic amines (HAAs), which are formed from the reaction of creatine or creatinine, amino acids, and sugars in meat and fish cooked at high temperatures, have been shown to be mutagenic in bacterial assays and carcinogenic in animal models. Following advances in the dietary assessment of HAA intake in epidemiological studies - including development of a validated meat-cooking module and a specialized food composition database - a number of epidemiological studies have specifically examined the association of HAA intake and cancer risk, most of which were conducted in Western countries. Given that dietary habits and cooking methods differ across countries, however, epidemiological investigation of dietary HAA intake requires a population-specific assessment method. Here, we developed a practical method for assessing dietary HAA intake among Japanese using a food frequency questionnaire (FFQ) and evaluated its validity for use in epidemiological studies by comparison with 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP) levels in human hair. The Japan Public Health Center-based Prospective Study reported that daily intake of HAAs among Japanese was relatively low, and that more than 50% of total intake in mainland Japan was derived from fish. Only four case-control studies in Japan have been reported so far, for colorectal, stomach and prostate cancer, and colorectal adenoma. A statistically significant positive association was found between 2-amino-3,4-dimethylimidazo [4,5-f] quinoline (MeIQ) and the risk of colorectal adenoma and between individual and total HAAs and the risk of prostate cancer. In contrast, no association was observed for colorectal or stomach cancer, or for colorectal adenoma among men. We also found that the limited and inconsistent findings among epidemiological studies are due to the difficulty in assessing exposure levels of HAAs. In addition to further evidence from prospective cohort studies in Japanese based on dietary HAA intake estimated by FFQs, studies using other methods to assess HAA exposure, such as biomarkers, are highly anticipated.

Metabolism and biomarkers of heterocyclic aromatic amines in humans

Heterocyclic aromatic amines (HAAs) form during the high-temperature cooking of meats, poultry, and fish. Some HAAs also arise during the combustion of tobacco. HAAs are multisite carcinogens in rodents, inducing cancer of the liver, gastrointestinal tract, pancreas, mammary, and prostate glands. HAAs undergo metabolic activation by N-hydroxylation of the exocyclic amine groups to produce the proposed reactive intermediate, the heteroaryl nitrenium ion, which is the critical metabolite implicated in DNA damage and genotoxicity. Humans efficiently convert HAAs to these reactive intermediates, resulting in HAA protein and DNA adduct formation. Some epidemiologic studies have reported an association between frequent consumption of well-done cooked meats and elevated cancer risk of the colorectum, pancreas, and prostate. However, other studies have reported no associations between cooked meat and these cancer sites. A significant limitation in epidemiology studies assessing the role of HAAs and cooked meat in cancer risk is their reliance on food frequency questionnaires (FFQ) to gauge HAA exposure. FFQs are problematic because of limitations in self-reported dietary history accuracy, and estimating HAA intake formed in cooked meats at the parts-per-billion level is challenging. There is a critical need to establish long-lived biomarkers of HAAs for implementation in molecular epidemiology studies designed to assess the role of HAAs in health risk. This review article highlights the mechanisms of HAA formation, mutagenesis and carcinogenesis, the metabolism of several prominent HAAs, and the impact of critical xenobiotic-metabolizing enzymes on biological effects. The analytical approaches that have successfully biomonitored HAAs and their biomarkers for molecular epidemiology studies are presented.

Food security, obesity, and meat-derived carcinogen exposure in US adults

Risk for colorectal cancer (CRC) is increased in adults with poor diet quality, low socioeconomic status, and increased body mass index (BMI). Cooked meats contain high contents of mutagenic compounds related to CRC risk. To explore differences in meat-based carcinogen exposure, a 99-item Qualtrics survey was issued to 1648 US adults. Average monthly serving size, degree of doneness, and cooking methods of meat products were obtained. The National Cancer Institute CHARRED database was used to quantify exposure to HCAs, PAHs, and Ames Predicted and Estimated mutagenicity. Questions from validated instruments assessed food security status (FSS) and demographic variables, while height and weight were self-reported to calculate BMI. Sex, FSS and obesity status (BMI > 30 kg/m²) were compared using two-sample t-tests and multivariate regression models to determine differences in meat intake and carcinogen exposure. Statistical significance was set at P < 0.05. Eight hundred fifty-six valid responses (57.4% female and 81.8% white) were obtained. Non-obese males consumed more white meat and were exposed to greater amounts of 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline. Food insecure and obese females consumed more red meat and had higher exposure rates of several carcinogens. Pan-frying and BBQ were the primary sources of meat-derived carcinogens. Greater disparities in carcinogen exposure were observed in females regarding BMI and FSS. Public health messages to modify meat cooking methods may be most effective for CRC prevention.

Red meat consumption, cooking mutagens, NAT1/2 genotypes and pancreatic cancer risk in two ethnically diverse prospective cohorts

There is limited evidence on the association between red meat consumption and pancreatic cancer among ethnic minorities. We assessed this relationship in two large prospective cohorts: the Multiethnic Cohort Study (MEC) and the Southern Community Cohort Study (SCCS). Demographic, dietary and other risk factor data were collected at cohort entry. Red meat intake was assessed using cohort-specific validated food frequency questionnaires. Incident pancreatic cancer cases were identified via linkages to state cancer registries. Cox regression was used to calculate relative risks (RRs) and 95% confidence intervals (CIs) for the association of red meat intake with pancreatic cancer risk in each cohort. We performed additional analyses to evaluate cooking methods, mutagens and effect modification by NAT1/2 genotypes. From a total of 184 542 (MEC) and 66 793 (SCCS) at-risk participants, we identified 1618 (MEC) and 266 (SCCS) incident pancreatic cancer cases. Red meat consumption was associated with pancreatic cancer risk in the MEC (RRQ4vsQ1 1.18, 95% CI 1.02-1.37) and with borderline statistical significance in the SCCS (RRQ4vsQ1 1.31, 95% CI 0.93-1.86). This association was significant in African Americans (RRQ4vsQ1 1.49, 95% CI 1.06-2.11) and Latinos (RRQ4vsQ1 1.44, 95% CI 1.02-2.04) in the MEC, and among African Americans (RRQ4vsQ1 1.55, 95% CI 1.03-2.33) in the SCCS. NAT2 genotypes appeared to modify the relationship between red meat and pancreatic cancer in the MEC (pinteraction = 0.03). Our findings suggest that the associations for red meat may be strongest in African Americans and Latinos. The mechanisms underlying the increased risk for these populations should be further investigated.

Characterizing Demographic and Geographical Differences in Health Beliefs and Dietary Habits Related to Colon Cancer Risk in US Adults

Background: Colon cancer (CC) risk is increased by behavioral factors including a diet high in red meat (RM) and processed meat; excess adiposity has contributed to a rise in CC in younger adults. The willingness of at-risk adults to modify behaviors to reduce CC risk warrants further investigation.

Methods: The previously validated Dietary Habits and Colon Cancer Beliefs Survey (DHCCBS) was used to assess attitudes and beliefs related to CC risk and diet behavior. An abbreviated food frequency questionnaire was included in the survey to quantify RM and green leafy vegetable (GLV) intake over the previous 30 days. Independent samples t-tests compared RM and GLV intake and DHCCBS responses. One-way analysis of variance with post-hoc LSD correction was completed to assess these differences within three age groups (<35, 35–44, and 45–54 years old) and between U.S. Census Bureau geographical regions.

Results: Eight hundred and thirty eight survey responses were analyzed. Perceived severity of CC diagnosis was significantly lower in younger adults (<35) compared to older adults (35–44, p = 0.042; 45–54, p = 0.003). Furthermore, younger adults (<35) perceived fewer barriers (i.e., taste preference) to GLV consumption than their older adult counterparts (35–44, p = 0.019; 45–54, p = 0.002). Few regional differences in habitual RM consumption were observed, however, several disparities were observed with GLV.

Conclusion: These findings from the DHCCBS indicate health beliefs toward CC risk are influenced by an individual's age and dietary habits. Additionally, regional differences in GLV consumption indicate opportunities for risk-reduction-focused health messages, particularly in the southern United States where CC incidence and mortality are highest.

Knowledge, attitudes and eating habits red and processed meat among gym users: a cross-sectional survey

Aims:

In 2015, the International Agency for Research on Cancer (IARC) classified red meat (RM) and processed meat (PM) intakes as ‘probably carcinogenic’ and ‘carcinogenic’ to humans, respectively. The aim of the study was to evaluate eating behaviours and knowledge on the potential risks of RM-PM consumption among gym users.

Methods:

In 2018, a cross-sectional survey was conducted in 20 gyms in Turin using a 48-item questionnaire assessing sociodemographic, sports, dietary information and knowledge about RM-PM (sample size = 298). Multivariable logistic and linear regressions were performed. The significance level was p ⩽ 0.05.

Results:

Around 75% of the sample consumed RM and PM at least once a week, with an average of 240.55 ± 435.99 g and 106.50 ± 157.88 g consumed weekly, respectively. Only 7.69% exceeded 700 g of raw RM weekly. Females, those with higher education, those who practise sport outside gyms and those who declared to practise sport to stay healthy, declared to consume less RM. Those who practise sport at a competitive level, those who are on a diet for athletic needs, those with higher body mass index (BMI) and those who consume more eggs and alcohol had a higher RM intake. The association with PM consumption was negative for females and positive for those living without a partner. The likelihood of answering incorrectly to one of the knowledge outcomes was lower for those who had a healthcare-related background and declared to practise sport to stay healthy, while it was higher for participants who stated to have a sport-related background, to be on a diet to lose weight, to read rarely/never the RM-PM nutrition labels and to consume <400 g of fruit and vegetables daily.

Conclusions:

Given the relatively low knowledge of the potential risks of RM-PM consumption, it would be advisable to implement campaigns specifically focused on male athletes and people with lower socioeconomic status, in order to raise awareness about this topic.

Determination of polycyclic aromatic hydrocarbon content in heat-treated meat retailed in Egypt: Health risk assessment, benzo[a]pyrene induced mutagenicity and oxidative stress in human colon (CaCo-2) cells and protection using rosmarinic and ascorbic acids

This study was undertaken to estimate the concentrations of the formed polycyclic aromatic hydrocarbons (PAHs) in heat-treated (boiled, pan-fried and grilled) meats collected from Egypt. Dietary intakes and cancer risks of PAHs among Egyptian adults were calculated. Benzo[a]pyrene (B[a]P)-induced mutagenicity and oxidative stress in human colon (CaCo-2) cell line and mechanisms behind such effects were also investigated. Finally, protection trials using rosmarinic (RMA) and ascorbic acids (ASA) were carried out. The results indicated formation of PAHs at high levels in the heat-treated meats. Calculated incremental life time cancer risk among Egyptian adults were 7.05179E-07, 7.00604 E-06 and 1.86069 E-05 due to ingestion of boiled, pan-fried and grilled meats, respectively. B[a]P-exposed CaCo-2 cells had high abilities for mutagenicity (490.05 ± 21.37 His + revertants) and production of reactive oxygen species. RMA and ASA protected CaCo-2 cells via reduction of B[a]P-induced mutagenicity and oxidative stress and upregulation of phase II detoxification enzymes and xenobiotic transporters.

Association between meat consumption and risk of breast cancer: Findings from the Sister Study

Meat consumption has been postulated to increase the risk of breast cancer, but this association has not been consistently seen. We examined the association between consumption of different types of meat, meat mutagens and incident invasive breast cancer. Information on consumption of different meat categories and meat cooking practice behaviors was obtained from 42,012 Sister Study participants who completed a Block 1998 Food Frequency Questionnaire at enrollment (2003-2009) and satisfied eligibility criteria. Exposure to meat type and meat mutagens was calculated, and associations with invasive breast cancer risk were estimated using multivariable Cox proportional hazards regression. During follow-up (mean, 7.6 years), 1,536 invasive breast cancers were diagnosed at least 1 year after enrollment. Increasing consumption of red meat was associated with increased risk of invasive breast cancer (HR_{highest vs. lowest quartile} :1.23, 95% CI: 1.02-1.48, p_trend = 0.01). Conversely, increasing consumption of poultry was associated with decreased invasive breast cancer risk (HR _{highest vs. lowest quartile} : 0.85; 95% CI: 0.72-1.00; p_trend = 0.03). In a substitution model with combined red meat and poultry consumption held constant, substituting poultry for red meat was associated with decreased invasive breast cancer risk (HR _{highest vs. lowest quartile} of poultry consumption: 0.72, 95% CI: 0.58-0.89). No associations were observed for cooking practices, estimated heterocyclic amines or heme iron from red meat consumption with breast cancer risk. Red meat consumption may increase the risk of invasive breast cancer, whereas poultry consumption may be associated with reduced risk. Substituting poultry for red meat could reduce breast cancer risk.

Vitamin C and Vitamin E Mitigate the Risk of Pancreatic Ductal Adenocarcinoma from Meat-Derived Mutagen Exposure in Adults in a Case-Control Study

BACKGROUND

Previous studies have found that meat-derived mutagens increase, and vitamin C or E decrease, the risk of pancreatic cancer.

OBJECTIVE

The aim of this study was to determine whether intake of vitamin C or E modulates the association between meat-derived mutagen exposure and risk of pancreatic cancer.

DESIGN

We conducted a case-control study in 1321 patients with pathologically confirmed pancreatic ductal adenocarcinoma (PDAC) and 1061 healthy controls (aged 28-88 y). Cases and controls were frequency-matched by age, sex, and race/ethnicity. Mutagen intake was assessed using a meat preparation questionnaire. Intakes of vitamin C, E, and other dietary components were assessed via a food-frequency questionnaire in a subset of 811 cases and 818 controls. ORs and 95% CIs were estimated in multivariable-adjusted logistic regression models.

RESULTS

The risk of PDAC was not associated with meat intake but was associated with consumption of well-done grilled or barbecued chicken (OR: 1.57; 95% CI: 1.18, 2.09; P = 0.001). Intake of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline was associated with increased PDAC risk (Ptrend = 0.047). Participants in the highest, as compared with the lowest, quintile of 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (PhIP) intake experienced a 38% increased risk of PDAC (95% CI: 1.00, 1.90; P = 0.048). Intakes of total vitamin C or E from food and supplements or from supplements alone were each inversely associated with PDAC risk. Stratified analyses showed differential associations for PhIP intake and PDAC risk, such that risk increased among individuals with lower intake of vitamin C or E and decreased among those with higher vitamin intake. Significant interactions of dietary vitamin C, dietary vitamin E, and total vitamin E with PhIP intake were detected (Pinteraction = 0.023, <0.001, and 0.013, respectively).

CONCLUSIONS

Consistent with experimental evidence, this study of 811 cases and 818 controls has shown that high intake of dietary vitamin C or E mitigates the risk of PhIP-related PDAC.

Development and Validation of the Dietary Habits and Colon Cancer Beliefs Survey (DHCCBS): An Instrument Assessing Health Beliefs Related to Red Meat and Green Leafy Vegetable Consumption

Dietary patterns characterized by higher red meat (RM) consumption are associated with increased colon cancer (CC) risk. Preclinical and epidemiological evidence suggest higher green leafy vegetable (GLV) consumption may mitigate these risks. Determining the relationship between dietary habits and expected health outcomes is needed. Methods. The Health Belief Model (HBM) was used to assess perceived CC susceptibility and severity, and related dietary benefits, barriers, and motivators. RM and GLV consumption were quantified using select DHQII items (n=15) capturing the previous 30 days' intake. A 34-item Qualtrics survey was provided to a convenience sample of 1,075 adults residing throughout the US Confirmatory factor analysis measured fitness with HBM, and Cronbach's alpha assessed subscale reliability. A subsample (n=47) completed a 2-week follow-up for test-retest reliability. Independent sample t-tests were used to compare RM and GLV intake and DHCCBS responses between genders. Individual barrier questions and RM and GLV consumption were compared using ANOVA for each gender; post hoc analyses between barrier question responses were assessed with Bonferroni correction. Results were considered significant with a p value of less than 0.05. Results. 990 US adults (52.7% female, 79.1% white, 50.8% aged 35+ years) completed valid surveys. Factor analysis with varimax rotation validated the construct of HBM subscales; only one question had a loading less than 0.745. Subscale Cronbach's alphas ranged within 0.478-0.845. Overall test-retest reliability was acceptable (r=0.697, p=5.22x10⁻⁸). Participant BMI was (mean±SD) 26.7±6.6 kg/m². Participants consumed (median, IQR) 2.3, 0.9-4.7 cooked cup equivalents GLV/week and 12.2, 5.8-21.5 ounces RM/week. Over half of respondents agreed or strongly agreed with the statement “I can't imagine never eating red meat,” while less than one eighth of respondents agreed or strongly agreed with the statement “I don't like the taste of green leafy vegetables.” Conclusion. The DHCCBS is a valid instrument for measuring health beliefs related to red meat, green leafy vegetables, and perceived colon cancer risk. Additionally, these findings suggest increasing GLV may be more feasible than reducing RM for CC risk reduction in meat eaters.

Different forms and sources of iron in relation to colorectal cancer risk: a case-control study in China

Few studies have examined the association of various types of Fe with colorectal cancer risk. The aim of this study was to investigate different forms and sources of Fe in relation to colorectal cancer risk in a Chinese population. A total of 2138 patients with colorectal cancer and 2144 sex- and age-matched (5-year interval) controls were recruited from July 2010 to November 2017. Dietary information was assessed by face-to-face interviews using a validated FFQ. Multivariable logistic regression was used to estimate the OR and 95 % CI on models. Intake of Fe from plants and Fe from white meat were inversely associated with the risk of colorectal cancer, while haem Fe and Fe from red meat were positively associated with colorectal cancer risk. The multivariable OR for the highest quartile v. the lowest quartile were 0·72 (95 % CI 0·59, 0·87, P trend&lt;0·001) for Fe from plants, 0·54 (95 % CI 0·45, 0·66, P trend&lt;0·001) for Fe from white meat, 1·26 (95 % CI 1·04, 1·53, P trend=0·005) for haem Fe and 1·83 (95 % CI 1·49, 2·24, P trend&lt;0·001) for Fe from red meat intake, respectively. However, no significant association was found between the consumption of total dietary Fe, non-haem Fe, Fe from meat and colorectal cancer risk. This study showed that lower intake of Fe from plants and white meat, as well as higher intake of haem Fe and Fe from red meat, were associated with colorectal cancer risk in a Chinese population.

Anatomical subsite can modify the association between meat and meat compounds and risk of colorectal adenocarcinoma: Findings from three large US cohorts

Distal and proximal colon tumors have distinct incidence trends and embryonic origins; whether these sub-sites have distinct susceptibilities to known risk factors is unclear. We used pooled data from 407,270 participants in three US-based studies, with overall median follow-up of 13.8 years. We used adjusted Cox models to analyze the association between dietary intakes (from diet history questionnaire) of total, processed and unprocessed red meat; total white meat, poultry and fish and meat-related compounds: heme iron, nitrate, nitrite, the heterocyclic amines (HCAs) and benzo(a)pyrene (B(a)P) and incidence of colorectal cancer subsites. The risk of colorectal cancer (n = 6,640) increased by 35% for each 50 g/1,000 kcal higher daily intake of total red meat, with a significant right-to-left trend from proximal colon (HR: 1.24; 95% CI: 1.09-1.39) to distal colon (HR: 1.34; 95% CI: 1.13-1.55) and rectum (HR: 1.53; 95% CI: 1.28-1.79). Only unprocessed red meat showed a significant right-to-left trend. Each 50 g/1,000 kcal increase in white meat intake was associated with a 26% reduction in total colorectal cancer risk (HR: 0.74; 95% CI: 0.68-0.80), with a significant inverse right-to-left trend. The highest quintile of heme iron was associated with increased cancer risk only in the distal colon (HR: 1.20; 95% CI: 1.02-1.42) and rectum (HR: 1.27; 95% CI: 1.07-1.52). The highest quintile of HCAs, and nitrate/nitrite were associated with increased risk of total colorectal cancer, but these associations did not vary across anatomical subsites. In summary, right and left subsites of the colon may have distinct susceptibilities to meat and possibly other dietary risk factors, suggesting that the causes of colorectal cancer may vary across anatomical subsites.

The association of diet, gut microbiota and colorectal cancer: what we eat may imply what we get

Despite the success of colonoscopy screening and recent advances in cancer treatment, colorectal cancer (CRC) still remains one of the most commonly diagnosed and deadly cancers, with a significantly increased incidence in developing countries where people are adapting to Western lifestyle. Diet has an important impact on risk of CRC. Multiple epidemiological studies have suggested that excessive animal protein and fat intake, especially red meat and processed meat, could increase the risk of developing CRC while fiber could protect against colorectal tumorigenesis. Mechanisms have been investigated by animal studies. Diet could re-shape the community structure of gut microbiota and influence its function by modulating the production of metabolites. Butyrate, one of the short-chain fatty acids (SCFAs), which act as a favorable source for colonocytes, could protect colonic epithelial cells from tumorigenesis via anti-inflammatory and antineoplastic properties through cell metabolism, microbiota homeostasis, antiproliferative, immunomodulatory and genetic/epigenetic regulation ways. In contrast, protein fermentation and bile acid deconjugation, which cause damage to colonic cells through proinflammatory and proneoplastic ways, lead to increased risk of developing CRC. In conclusion, a balanced diet with an increased abundance of fiber should be adopted to reduce the risk and prevent CRC.

Meat Cooking Methods and Risk of Type 2 Diabetes: Results From Three Prospective Cohort Studies

OBJECTIVE

To examine open-flame and/or high-temperature cooking (grilling/barbecuing, broiling, or roasting) and doneness preferences (rare, medium, or well done) for red meat, chicken, and fish in relation to type 2 diabetes (T2D) risk among U.S. adults who consumed animal flesh regularly (≥2 servings/week).

RESEARCH DESIGN AND METHODS

The prospective studies included 52,752 women from the Nurses' Health Study (NHS) (followed during 1996-2012), 60,809 women from NHS II (followed during 2001-2013), and 24,679 men from the Health Professionals Follow-Up Study (HPFS) (followed during 1996-2012) who were free of diabetes, cardiovascular disease, and cancer at baseline. Incident cases of T2D were confirmed by validated supplementary questionnaires.

RESULTS

We documented 7,895 incident cases of T2D during 1.74 million person-years of follow-up. After multivariate adjustments including baseline BMI and total consumption of red meat, chicken, and fish, higher frequency of open-flame and/or high-temperature cooking was independently associated with an elevated T2D risk. When comparing open-flame and/or high-temperature cooking >15 times/month with <4 times/month, the pooled hazard ratio (HR) (95% CI) of T2D was 1.28 (1.18, 1.39; Ptrend <0.001). When comparing the extreme quartiles of doneness-weighted frequency of high-temperature cooking, the pooled HR (95% CI) of T2D was 1.20 (1.12, 1.28; Ptrend <0.001). These associations remained significant when red meat and chicken were examined separately. In addition, estimated intake of heterocyclic aromatic amines was also associated with an increased T2D risk.

CONCLUSIONS

Independent of consumption amount, open-flame and/or high-temperature cooking for both red meat and chicken is associated with an increased T2D risk among adults who consume animal flesh regularly.

Calculation of Haem Iron Intake and Its Role in the Development of Iron Deficiency in Young Women from the Australian Longitudinal Study on Women's Health

Total iron intake is not strongly associated with iron stores, but haem iron intake may be more predictive. Haem iron is not available in most nutrient databases, so experimentally determined haem contents were applied to an Australian Food Frequency Questionnaire (FFQ) to estimate haem iron intake in a representative sample of young women (25–30 years). The association between dietary haem iron intakes and incident self-reported diagnosed iron deficiency over six years of follow-up was examined. Haem iron contents for Australian red meats, fish, and poultry were applied to haem-containing foods in the Dietary Questionnaire for Epidemiological Studies V2 (DQESv2) FFQ. Haem iron intakes were calculated for 9076 women from the Australian Longitudinal Study on Women’s Health (ALSWH) using the DQESv2 dietary data from 2003. Logistic regression was used to examine the association between haem iron intake (2003) and the incidence of iron deficiency in 2006 and 2009. Multiple logistic regression showed baseline haem iron intake was a statistically significant predictor of iron deficiency in 2006 (Odds Ratio (OR): 0.91; 95% Confidence Interval (CI): 0.84–0.99; p-value: 0.020) and 2009 (OR: 0.89; 95% CI: 0.82–0.99; p-value: 0.007). Using the energy-adjusted haem intake made little difference to the associations. Higher haem iron intake is associated with reduced odds of iron deficiency developing in young adult Australian women.

Dietary Intake of Meat Cooking-Related Mutagens (HCAs) and Risk of Colorectal Adenoma and Cancer: A Systematic Review and Meta-Analysis

Much evidence suggests that the positive association between meat intake and colorectal adenoma (CRA) and cancer (CRC) risk is mediated by mutagenic compounds generated during cooking at high temperature. A number of epidemiological studies have estimated the effect of meat-related mutagens intake on CRC/CRA risk with contradictory and sometimes inconsistent results. A literature search was carried out (PubMed, Web of Science and Scopus) to identify articles reporting the relationship between the intake of meat-related mutagens (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f] quinoxaline: DiMeIQx, benzo(a) pyrene (B(a)P) and "meat derived mutagenic activity" (MDM)) and CRC/CRA risk. A random-effect model was used to calculate the risk association. Thirty-nine studies were included in the systematic review and meta-analysis. Polled CRA risk (15229 cases) was significantly increased by intake of PhIP (OR = 1.20; 95% CI: 1.13,1.28; p < 0.001), MeIQx (OR = 1.14; 95% CI: 1.05,1.23; p = 0.001), DiMeIQx (OR = 1.13; 95% CI: 1.05,1.21; p = 0.001), B(a)P (OR = 1.10; 95% CI: 1.02,1.19; p = 0.017) and MDM (OR = 1.17; 95% CI: 1.07,1.28; p = 0.001). A linear and curvilinear trend was observed in dose-response meta-analysis between CRA risk in association with PhIP, MDM, and MeIQx. CRC risk (21,344 cases) was increased by uptake of MeIQx (OR = 1.14; 95% CI: 1.04,1.25; p = 0.004), DiMeIQx (OR = 1.12; 95% CI: 1.02,1.22; p = 0.014) and MDM (OR = 1.12; 95% CI: 1.06,1.19; p < 0.001). No publication bias could be detected, whereas heterogeneity was in some cases rather high. Mutagenic compounds formed during cooking of meat at high temperature may be responsible of its carcinogenicity.

Mortality from different causes associated with meat, heme iron, nitrates, and nitrites in the NIH-AARP Diet and Health Study: population based cohort study

Objective To determine the association of different types of meat intake and meat associated compounds with overall and cause specific mortality.Design Population based cohort study.Setting Baseline dietary data of the NIH-AARP Diet and Health Study (prospective cohort of the general population from six states and two metropolitan areas in the US) and 16 year follow-up data until 31 December 2011.Participants 536 969 AARP members aged 50-71 at baseline.Exposures Intake of total meat, processed and unprocessed red meat (beef, lamb, and pork) and white meat (poultry and fish), heme iron, and nitrate/nitrite from processed meat based on dietary questionnaire. Adjusted Cox proportional hazards regression models were used with the lowest fifth of calorie adjusted intakes as reference categories.Main outcome measure Mortality from any cause during follow-up.Results An increased risk of all cause mortality (hazard ratio for highest versus lowest fifth 1.26, 95% confidence interval 1.23 to 1.29) and death due to nine different causes associated with red meat intake was observed. Both processed and unprocessed red meat intakes were associated with all cause and cause specific mortality. Heme iron and processed meat nitrate/nitrite were independently associated with increased risk of all cause and cause specific mortality. Mediation models estimated that the increased mortality associated with processed red meat was influenced by nitrate intake (37.0-72.0%) and to a lesser degree by heme iron (20.9-24.1%). When the total meat intake was constant, the highest fifth of white meat intake was associated with a 25% reduction in risk of all cause mortality compared with the lowest intake level. Almost all causes of death showed an inverse association with white meat intake.Conclusions The results show increased risks of all cause mortality and death due to nine different causes associated with both processed and unprocessed red meat, accounted for, in part, by heme iron and nitrate/nitrite from processed meat. They also show reduced risks associated with substituting white meat, particularly unprocessed white meat.

Dietary Iron and Colorectal Cancer Risk: A Review of Human Population Studies

Iron is an essential micronutrient that is involved in many redox processes and serves as an integral component in various physiological functions. However, excess iron can cause tissue damage through its pro-oxidative effects, potentiating the development of many diseases such as cancer through the generation of reactive oxidative species. The two major forms of iron in the diet are heme and nonheme iron, both of which are found in several different foods. In addition to natural food sources, intake of nonheme iron may also come from fortified foods or in supplement form. This review summarizes the results of human population studies that have examined the role of dietary iron (heme and nonheme), heme iron alone, and iron from supplements in colorectal carcinogenesis.

Cancer in Japan: Prevalence, prevention and the role of heterocyclic amines in human carcinogenesis

In this article, three topics are being studied in order to understand the present state of cancer in Japan. First, the statistics on cancer mortality indicates that the mortality from cancer in young individuals has been decreasing during the last 50 years, although the total mortality from cancer has been steadily and steeply increasing. Second, epidemiological analyses of cancer causes in Japan indicated that 50 % of cancer cases are preventable, and that prevention of infection and refraining from tobacco smoking will reduce cancer mortality by about 40 %. Third, mutagenic/carcinogenic heterocyclic amines present in cooked meat/fish have been suggested to be carcinogenic in humans in many epidemiological studies carried out in Japan and other countries.

Are meat and heme iron intake associated with pancreatic cancer? Results from the NIH-AARP diet and health cohort

Several studies on pancreatic cancer have reported significant positive associations for intake of red meat but null associations for heme iron. We assessed total, red, white and processed meat intake, meat cooking methods and doneness and heme iron and mutagen intake in relation to pancreatic cancer in the NIH-AARP Diet and Health Study cohort. A total of 322,846 participants (187,265 men and 135,581 women) successfully completed and returned the food frequency questionnaire between 1995 and 1996. After a mean follow-up of 9.2 years (up to 10.17 years), 1,417 individuals (895 men and 522 women) developed exocrine pancreatic cancer. Cox proportional hazard models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs), and trends were calculated using the median value of each quantile. Models incorporated age as the time metric and were adjusted for smoking history, body mass index, self-reported diabetes and energy-adjusted saturated fat. Pancreatic cancer risk significantly increased with intake of total meat (Q5 vs. Q1: HR = 1.20, 95% CI 1.02-1.42, p-trend = 0.03), red meat (HR = 1.22, 95% CI 1.01-1.48, p-trend = 0.02), high-temperature cooked meat (HR = 1.21, 95% CI 1.00-1.45, p-trend = 0.02), grilled/barbequed meat (HR = 1.24, 95% CI 1.03-1.50, p-trend = 0.007), well/very well done meat (HR = 1.32, 95% CI 1.10-1.58, p-trend = 0.005) and heme iron from red meat (Q4 vs. Q1: HR = 1.21, 95% CI 1.01-1.45, p-trend = 0.04). When stratified by sex, these associations remained significant in men but not women except for white meat intake in women (HR = 1.33, 95% CI 1.02-1.74, p-trend = 0.04). Additional studies should confirm our findings that consuming heme iron from red meat increases pancreatic cancer risk.

Development and calibration of a dietary nitrate and nitrite database in the NIH-AARP Diet and Health Study

OBJECTIVE

Nitrate and nitrite are probable human carcinogens when ingested under conditions that increase the formation of N-nitroso compounds. There have been limited efforts to develop US databases of dietary nitrate and nitrite for standard FFQ. Here we describe the development of a dietary nitrate and nitrite database and its calibration.

DESIGN

We analysed data from a calibration study of 1942 members of the NIH-AARP (NIH-AARP, National Institutes of Health-AARP) Diet and Health Study who reported all foods and beverages consumed on the preceding day in two non-consecutive 24 h dietary recalls (24HR) and completed an FFQ. Based on a literature review, we developed a database of nitrate and nitrite contents for foods reported on these 24HR and for food category line items on the FFQ. We calculated daily nitrate and nitrite intakes for both instruments, and used a measurement error model to compute correlation coefficients and attenuation factors for the FFQ-based intake estimates using 24HR-based values as reference data.

RESULTS

FFQ-based median nitrate intake was 68·9 and 74·1 mg/d, and nitrite intake was 1·3 and 1·0 mg/d, in men and women, respectively. These values were similar to 24HR-based intake estimates. Energy-adjusted correlation coefficients between FFQ- and 24HR-based values for men and women respectively were 0·59 and 0·57 for nitrate and 0·59 and 0·58 for nitrite; energy-adjusted attenuation factors were 0·59 and 0·57 for nitrate and 0·47 and 0·38 for nitrite.

CONCLUSIONS

The performance of the FFQ in assessing dietary nitrate and nitrite intakes is comparable to that for many other macro- and micronutrients.

Red and processed meat, nitrite, and heme iron intakes and postmenopausal breast cancer risk in the NIH-AARP Diet and Health Study

Previous studies have shown inconsistent associations between red and processed meat intake and breast cancer risk. N-nitroso compounds and heme iron have been hypothesized as contributing factors. We followed 193,742 postmenopausal women in the NIH-AARP Diet and Health Study and identified 9,305 incident breast cancers (1995-2006). Dietary intake was assessed using a food frequency questionnaire at baseline. We adjusted daily intakes of meat, nitrite and heme iron for energy intake using the nutrient density method. We estimated multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) by quintiles of dietary exposures for all breast cancer, by stage (in-situ, localized, regional/distant) and by estrogen/progesterone receptor (ER/PR) status using Cox proportional hazards regression. Total red meat intake was positively associated with risk of regional/distant cancer (p-trend = 0.02). The risk was 25% higher in the highest vs. lowest intake quintile (95% CI = 1.03-1.52). Higher processed red meat intake (Q5 vs. Q1) was associated with 27% higher risk of localized breast cancer (95% CI = 1.01-1.27, p-trend = 0.03) and a 19% higher risk of regional/distant cancer (95% CI = 0.98-1.44, p-trend = 0.10). In addition, higher nitrite intake from processed red meat was positively associated with localized cancer (HR for Q5 vs. Q1 = 1.23, 95% CI = 1.09-1.39, p-trend < 0.0001). Heme iron intake was positively associated with breast cancer risk overall and all cancer stages (p-trend = 0.02-0.05). No heterogeneity was observed in risk associations by hormone receptor status. Our findings suggest that high consumption of red meat and processed meat may increase risk of postmenopausal breast cancer. Added nitrite and heme iron may partly contribute to these observed associations.

Gene-environment interaction of genome-wide association study-identified susceptibility loci and meat-cooking mutagens in the etiology of renal cell carcinoma

BACKGROUND

Meat-cooking mutagens may be associated with renal cell carcinoma (RCC) risk. In the current study, the authors examined associations between meat-cooking mutagens, genetic susceptibility variants, and risk of RCC.

METHODS

The authors used 659 newly diagnosed RCC cases and 699 healthy controls to investigate the association between dietary intake of meat-cooking mutagens and RCC. They examined whether associations varied by risk factors for RCC and genetic susceptibility variants previously identified from genome-wide association studies. Odds ratios and 95% confidence intervals were estimated using tertiles of intake of dietary polycyclic aromatic hydrocarbons/heterocyclic amines.

RESULTS

Dietary intake of the mutagenic compounds 2-amino-3,8-dimethylimidazo-(4,5-f) quinoxaline (MeIQx) and 2-amino-1 methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) were found to be significantly associated with an increased risk of RCC (odds ratios across tertiles: 1.00 [referent], 1.28 [95% confidence interval, 0.94-1.74], and 1.95 [95% confidence interval, 1.43-2.66] [P for trend <.001], respectively; and 1.00 [referent], 1.41 [95% confidence interval, 1.04-1.90], and 1.54 [95% confidence interval, 1.14-2.07] [P for trend =.02], respectively). The authors observed evidence of interactions between PhIP and RCC susceptibility variants in 2 genes: inositol 1,4,5-trisphosphate receptor, type 2 (ITPR2) (rs718314; multiplicative P for interaction = .03 and additive P for interaction =.002) and endothelial PAS domain-containing protein 1 (EPAS1) (rs7579899; additive P for interaction =.06).

CONCLUSIONS

The intake of meat may increase the risk of RCC through mechanisms related to the cooking compounds MeIQx and PhIP. These associations may be modified by genetic susceptibility to RCC. Further research is necessary to understand the biological mechanisms underlying these interactions.

Intake of Meat Mutagens and Risk of Prostate Cancer in a Cohort of U.S. Health Professionals

BACKGROUND

Evidence relating heterocyclic aromatic amines (HCA), associated with high-temperature cooking methods, to prostate cancer risk is inconsistent.

METHODS

In a large U.S. cohort study, intakes of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) and a meat-derived mutagenicity (MDM) index were assessed using a cooking method questionnaire administered in 1996. Until 2010, 2,770 prostate cancer cases were observed among 26,030 participants.

RESULTS

Intake of PhIP from red meat was statistically significantly associated with total prostate cancer risk (top vs. bottom quintile HR, 1.18; 95% confidence intervals; CI, 1.03-1.35), but not other HCAs (MeIQx, 1.12; 0.98-1.27, PhIP from white meat, 1.08; 0.95-1.22, DiMeIQx, 1.09; 0.97-1.21) or MDM (1.13; 1.00-1.28). For high-grade (Gleason sum 7 with pattern 4+3 and Gleason sum 8-10, n = 483 cases) and advanced cancers (n = 281), we only observed positive associations for PhIP from red meat (top vs. bottom quintile: high grade: HR, 1.44; 95% CI, 1.04-1.98, Ptrend = 0.03; advanced: HR, 1.50; 95% CI, 0.99-2.26; Ptrend = 0.12), but associations for advanced cancers did not reach statistical significance. Observed associations remained similar after adjustment for total, unprocessed, or processed red meat intake.

CONCLUSION

Observed positive associations between PhIP intake from red meat and prostate cancer, particularly high-grade and possibly also advanced prostate cancer, need to be confirmed in other studies.

IMPACT

Results do not provide strong evidence that HCAs increase risk of prostate cancers.

Polycyclic aromatic hydrocarbons and childhood asthma

Asthma is the most common chronic illness in children living in developed countries and the leading cause of childhood hospitalization and school absenteeism. Prevalence rates of asthma are increasing and show disparities across gender, geographic regions, and ethnic/racial groups. Common risk factors for developing childhood asthma include exposure to tobacco smoke, previous allergic reactions, a family history of asthma, allergic rhinitis or eczema, living in an urban environment, obesity and lack of physical exercise, severe lower respiratory tract infections, and male gender. Asthma exacerbation in children can be triggered by a variety of factors, including allergens (e.g., pollen, dust mites, and animal dander), viral and bacterial infections, exercise, and exposure to airway irritants. Recent studies have shown that exposure to polycyclic aromatic hydrocarbons (PAHs), a major component of fine particulate matter from combustion sources, is also associated with onset of asthma, and increasing asthmatic symptoms. In this paper, we review sources of childhood PAH exposure and the association between airborne PAH exposure and childhood asthma prevalence and exacerbation.

Dietary consumption of advanced glycation end products and pancreatic cancer in the prospective NIH-AARP Diet and Health Study

BACKGROUND

Advanced glycation end products (AGEs) are a heterogeneous group of compounds present in uncooked foods as well as in foods cooked at high temperatures. AGEs have been associated with insulin resistance, oxidative stress, and chronic inflammation in patients with diabetes. Dietary AGEs are an important contributor to the AGE pool in the body. N(ϵ)-(carboxymethyl)lysine (CML) AGE is one of the major biologically and chemically well-characterized AGE markers. The consumption of red meat, which is CML-AGE rich, has been positively associated with pancreatic cancer in men.

OBJECTIVES

With the use of a published food CML-AGE database, we estimated the consumption of CML AGE in the prospective NIH-AARP Diet and Health Study and evaluated the association between CML-AGE consumption and pancreatic cancer and the mediating effect of CML AGE on the association between red meat consumption and pancreatic cancer.

DESIGN

Multivariate Cox proportional hazard regression models were used to estimate HRs and 95% CIs for pancreatic cancer.

RESULTS

During an average of 10.5 y of follow-up, we identified 2193 pancreatic cancer cases (1407 men and 786 women) from 528,251 subjects. With the comparison of subjects in the fifth and the first quintiles of CML-AGE consumption, we observed increased pancreatic cancer risk in men (HR: 1.43; 95% CI: 1.06, 1.93, P-trend = 0.003) but not women (HR: 1.14; 95% CI: 0.76, 1.72, P-trend = 0.42). Men in the highest quintile of red meat consumption had higher risk of pancreatic cancer (HR: 1.35; 95% CI: 1.07, 1.70), which attenuated after adjustment for CML-AGE consumption (HR: 1.20; 95% CI: 0.95, 1.53).

CONCLUSION

Dietary CML-AGE consumption was associated with modestly increased risk of pancreatic cancer in men and may partially explain the positive association between red meat and pancreatic cancer.

Meat, dairy, and cancer

In 2007 the World Cancer Research Fund and American Institute for Cancer Research (WCRF/AICR) report judged that the evidence for an association between red and processed meat consumption and colorectal cancer was convincing. In addition, the effect of other animal products on cancer risk has been studied, and the WCRF/AICR report concluded that milk probably decreases the risk of colorectal cancer but diets high in calcium probably increase the risk of prostate cancer, whereas there was limited evidence for an association between milk and bladder cancer and insufficient evidence for other cancers. There are several potential mechanisms relating meat to cancer, including heterocyclic amines, polycyclic aromatic hydrocarbons, N-nitroso compounds, and heme iron. Although the evidence in favor of a link between red and processed meat and colorectal cancer is convincing, the relations with other cancers are unclear. In this review, we summarize cohort studies conducted by the National Cancer Institute on meat and dairy intake in relation to cancer since the 2007 WCRF/AICR report. We also report the findings of meta-analyses published since 2007.

Dietary iron, iron homeostatic gene polymorphisms and the risk of advanced colorectal adenoma and cancer

Dietary iron intake and variation in iron homeostasis genes may affect colorectal neoplasia risk. We conducted two nested case-control studies within the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial: one of advanced colorectal adenoma (1205 cases; 1387 controls) and one of colorectal cancer (370 cases; 401 controls). Iron intake was estimated with a food frequency questionnaire and genotyping was performed for 21 genes. Unconditional logistic regression was used to estimate odds ratio (OR) and 95% confidence intervals (95% CIs) for colorectal neoplasia risk within quartiles of intake. Several single nucleotide polymorphisms (SNPs) modified the association between iron intake and the risk of adenoma or cancer. Dietary iron was positively associated with colorectal adenoma among three SNPs of HEPHL1, including carriers of the AA genotype at rs7946162 (ORQ4-Q1 = 2.22, 95% CI 1.15-4.27, Ptrend = 0.03; Pinteraction = 0.10), the TT genotype at rs2460063 (ORQ4-Q1 = 2.39, 95% CI 1.26-4.54, Ptrend = 0.02; Pinteraction = 0.04) and the GG genotype at rs7127348 (ORQ4-Q1 = 2.40, 95% CI 1.23-4.67, Ptrend = 0.02; Pinteraction = 0.09). Heme iron was positively associated with colorectal cancer among those with GG genotypes for ACO1 rs10970985 (ORQ4-Q 1 = 2.45, 95% CI 3.40-8.06, Ptrend = 0.004; Pinteraction = 0.05). However, none of the associations were statistically significant after adjustment for multiple comparisons. Future studies should target the specific genes and SNPs for which the association was significant prior to multiple comparison correction.

Cancer-promoting and Inhibiting Effects of Dietary Compounds: Role of the Aryl Hydrocarbon Receptor (AhR)

Polyaromatic hydrocarbons, heterocyclic aromatic amines and dioxin-like compounds are environmental carcinogens shown to initiate cancer in a number of tissue types including prostate and breast. These environmental carcinogens elicit their effects through interacting with the aryl hydrocarbon receptor (AhR), a ligand activated transcription factor. Naturally occurring compounds found in fruits and vegetables shown to have anti-carcinogenic effects also interact with the AhR. This review explores dietary and environmental exposure to chemical carcinogens and beneficial natural compounds whose effects are elicited by the AhR.

Heme-induced biomarkers associated with red meat promotion of colon cancer are not modulated by the intake of nitrite

Red and processed meat consumption is associated with the risk of colorectal cancer. Three hypotheses are proposed to explain this association, via heme-induced oxidation of fat, heterocyclic amines, or N-nitroso compounds. Rats have often been used to study these hypotheses, but the lack of enterosalivary cycle of nitrate in rats casts doubt on the relevance of this animal model to predict nitroso- and heme-associated human colon carcinogenesis. The present study was thus designed to clarify whether a nitrite intake that mimics the enterosalivary cycle can modulate heme-induced nitrosation and fat peroxidation. This study shows that, in contrast with the starting hypothesis, drinking water added with nitrite to mimic the salivary nitrite content did not change the effect of hemoglobin on biochemical markers linked to colon carcinogenesis, notably lipid peroxidation and cytotoxic activity in the colon of rat. However, ingested sodium nitrite increased fecal nitroso-compounds level, but their fecal concentration and their nature (iron-nitrosyl) would probably not be associated with an increased risk of cancer. We thus suggest that the rat model could be relevant for study the effect of red meat on colon carcinogenesis, in spite of the lack of nitrite in the saliva of rats.

Influence of dietary fat type on benzo(a)pyrene [B(a)P] biotransformation in a B(a)P-induced mouse model of colon cancer

In the US alone, around 60,000 lives/year are lost due to colon cancer. Diet and environment have been implicated in the development of sporadic colon tumors. The objective of this study was to determine how dietary fat potentiates the development of colon tumors through altered B(a)P biotransformation, using the Adenomatous polyposis coli with Multiple intestinal neoplasia mouse model. Benzo(a)pyrene was administered to mice through tricaprylin, and unsaturated (USF; peanut oil) and saturated (SF; coconut oil) fats at doses of 50 and 100 μg/kg via oral gavage over a 60-day period. Blood, colon, and liver were collected at the end of exposure period. The expression of B(a)P biotransformation enzymes [cytochrome P450 (CYP)1A1, CYP1B1 and glutathione-S-transferase] in liver and colon were assayed at the level of protein, mRNA and activities. Plasma and tissue samples were analyzed by reverse phase high-performance liquid chromatography for B(a)P metabolites. Additionally, DNA isolated from colon and liver tissues was analyzed for B(a)P-induced DNA adducts by the (32)P-postlabeling method using a thin-layer chromatography system. Benzo(a)pyrene exposure through dietary fat altered its metabolic fate in a dose-dependent manner, with 100 μg/kg dose group registering an elevated expression of B(a)P biotransformation enzymes, and greater concentration of B(a)P metabolites, compared to the 50 μg/kg dose group (P<.05). This effect was more pronounced for SF group compared to USF group (P<.05). These findings establish that SF causes sustained induction of B(a)P biotransformation enzymes and extensive metabolism of this toxicant. As a consequence, B(a)P metabolites were generated to a greater extent in colon and liver, whose concentrations also registered a dose-dependent increase. These metabolites were found to bind with DNA and form B(a)P-DNA adducts, which may have contributed to colon tumors in a subchronic exposure regimen.

Bioaccessibility of polycyclic aromatic hydrocarbons: relevance to toxicity and carcinogenesis

INTRODUCTION

Bioaccessibility is a growing area of research in the field of risk assessment. As polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants, they are the toxicants of focus to establish cancer risks in humans. Orally ingested PAHs also cause toxicity and even affect the pharmacokinetic behavior of some therapeutic agents. Toward this end, bioaccessibility is being used as a tool to assess the risk of PAHs via dietary exposures.

AREAS COVERED

This review covers some in vitro bioaccessibility models for PAHs that have been used for the past one-and-a-half decade. This review also considers the factors that influence bioaccessibility and debates the merits and limitations of using a bioaccessibility concept for estimating risk from ingestion of PAH-contaminated soil and food. Finally, the authors discuss the implications of bioaccessibility for PAH-induced toxicity and cancers in the context of risk assessment.

EXPERT OPINION

So far, much of the focus on PAH bioaccessibility is centered on soil as a preferential matrix. However, ingestion of PAHs through diet far exceeds the amount accidentally ingested through soil. Therefore, bioaccessibility could be exploited as a tool to assess the relative risk of various dietary ingredients tainted with PAHs. While bioaccessibility is a promising approach for assessing PAH risk arising from various types of contaminated soils, none of the models proposed appears to be valid. Bioaccessibility values, derived from in vitro studies, still require validation from in vivo studies.

Red meat-derived heterocyclic amines increase risk of colon cancer: a population-based case-control study

Formation of mutagenic heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) is one pathway believed to drive the association of colon cancer with meat consumption. Limited data exist on the associations of individual HCAs and PAHs in red or white meat with colon cancer. Analyzing data from a validated meat preparation questionnaire completed by 1062 incident colon cancer cases and 1645 population controls from an ongoing case-control study, risks of colon cancer were estimated using unconditional logistic regression models, comparing the fourth to the first quartile of mutagen estimates derived from a CHARRED based food frequency questionnaire. Total dietary intake of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) [adjusted odds ratio (aOR) = 1.87, 95% confidence interval (CI) = 1.44-2.44, P(trend) < 0.0001], 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) (aOR = 1.68, 95% CI = 1.29-2.17, P(trend) = 0.001) and meat-derived mutagenic activity (aOR = 1.77, 95% CI = 1.36-2.30, P(trend) < 0.0001) were statistically significantly associated with colon cancer risk. Meat type specific analyses revealed statistically significant associations for red meat-derived MeIQx, DiMeIQx, and mutagenic activity but not for the same mutagens derived from white meat. Our study adds evidence supporting red meat-derived, but not white-meat derived HCAs and PAHs, as an important pathway for environmental colon cancer carcinogenesis.

Dietary heme iron and the risk of colorectal cancer with specific mutations in KRAS and APC

Red meat intake has been linked to increased colorectal cancer (CRC) risk. Although the underlying mechanisms remain unclear, experimental studies suggest a role for dietary heme iron. Because heme iron was shown to promote specific mutations, it would be insightful to link heme iron data to CRC with mutations in key genes in an observational, population-based study. We investigated the association between dietary heme iron intake and risk of CRC with mutations in APC (adenomatous polyposis coli) and KRAS (Kirsten ras) and P53 overexpression in the Netherlands Cohort Study. After 7.3 years of follow-up, excluding the first 2.3 years due to incomplete coverage of the pathology registry and to avoid preclinical disease, adjusted hazard ratios (including adjustment for total meat) and 95% confidence intervals were calculated, using 4026 subcohort members (aged 55-69 years at baseline), 435 colon and 140 rectal cancer patients. When comparing the highest with the lowest tertile of intake, heme iron intake was associated with an increased risk of CRC harboring activating mutations in KRAS (hazard ratio = 1.71, 95% confidence interval: 1.15-2.57; P for trend = 0.03) and CRC without truncating mutations in APC (hazard ratio = 1.79, 95% confidence interval: 1.23-2.60; P for trend = 0.003). We observed a positive association between heme iron intake and the risk of CRC with activating G>A mutations in KRAS (P for trend = 0.01) and overall G>A mutations in APC (P for trend = 0.005). No associations were found with CRC harboring G>T mutations in KRAS/APC. Heme iron intake was positively associated with the risk of P53 overexpressed tumors but not with tumors without P53 overexpression (Pheterogeneity = 0.12). Heme iron intake was associated with an increased risk of colorectal tumors harboring G>A transitions in KRAS and APC and overexpression of P53. These novel findings suggest that alkylating rather than oxidative DNA-damaging mechanisms are involved in heme-induced colorectal carcinogenesis.

A prospective investigation of fish, meat and cooking-related carcinogens with endometrial cancer incidence

Background:

There are limited prospective studies of fish and meat intakes with risk of endometrial cancer and findings are inconsistent.

Methods:

We studied associations between fish and meat intakes and endometrial cancer incidence in the large, prospective National Institutes of Health-AARP Diet and Health Study. Intakes of meat mutagens 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) and benzo(a)pyrene (BaP) were also calculated. We used Cox proportional hazards regression models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

Results:

We observed no associations with endometrial cancer risk comparing the highest to lowest intake quintiles of red (HR=0.91, 95% CI 0.77–1.08), white (0.98, 0.83–1.17), processed meats (1.02, 0.86–1.21) and fish (1.10, 95% CI 0.93–1.29). We also found no associations between meat mutagen intakes and endometrial cancer.

Conclusion:

Our findings do not support an association between meat or fish intakes or meat mutagens and endometrial cancer.

Meat-related mutagens and pancreatic cancer: null results from a clinic-based case-control study

BACKGROUND

Pancreatic cancer is a devastating disease for which the role of dietary factors remains inconclusive. The study objective was to evaluate risk of pancreatic cancer associated with meat preparation methods and meat-related mutagen consumption using a clinic-based case-control design.

METHODS

There were 384 cases and 983 controls; subjects provided demographic information and completed a 144-item food frequency questionnaire, which was used to estimate meat mutagen intake using the National Cancer Institute's CHARRED database (Bethesda, MD). Logistic regression was used to calculate ORs and 95% confidence intervals (CI), adjusted for factors including age, sex, cigarette smoking, body mass index, and diabetes mellitus.

RESULTS

Overall, the findings were null with respect to meat mutagen intake and pancreatic cancer.

CONCLUSIONS

The results do not support an association between well-done meat or meat-related mutagen intake and pancreatic cancer and contrast with generally increased risks reported in previous studies.

IMPACT

These data contribute to evidence about pancreatic cancer and potentially carcinogenic compounds in meat.

Meat intake, cooking methods and risk of proximal colon, distal colon and rectal cancer: the Norwegian Women and Cancer (NOWAC) cohort study

Red and processed meat intake is an established risk factor for colorectal cancer (CRC), but epidemiological evidence by subsite and sex is still limited. In the population-based Norwegian Women and Cancer cohort, we examined associations of meat intake with incident proximal colon, distal colon and rectal cancer, in 84,538 women who completed a validated food frequency questionnaire (FFQ) during 1996-1998 or 2003-2005 (baseline or exposure update) at age 41-70 years, with follow-up by register linkages through 2009. We also examined the effect of meat cooking methods in a subsample (n = 43,636). Multivariable hazard ratios (HRs) were estimated by Cox regression. There were 459 colon (242 proximal and 167 distal), and 215 rectal cancer cases with follow-up ≥ 1 (median 11.1) year. Processed meat intake ≥60 vs. <15 g/day was associated with significantly increased cancer risk in all subsites with HRs (95% confidence interval, CI) of 1.69 (1.05-2.72) for proximal colon, 2.13 (1.18-3.83) for distal colon and 1.71 (1.02-2.85) for rectal cancer. Regression calibration of continuous effects based on repeated 24-hr dietary recalls, indicated attenuation due to measurement errors in FFQ data, but corrected HRs were not statistically significant due to wider CIs. Our study did not support an association between CRC risk and intake of red meat, chicken, or meat cooking methods, but a high processed meat intake was associated with increased risk of proximal colon, distal colon and rectal cancer. The effect of processed meat was mainly driven by the intake of sausages.

Dietary intake of nitrate and nitrite and risk of renal cell carcinoma in the NIH-AARP Diet and Health Study

BACKGROUND

Nitrate and nitrite are present in many foods and are precursors of N-nitroso compounds, known animal carcinogens and potential human carcinogens. We prospectively investigated the association between nitrate and nitrite intake from dietary sources and risk of renal cell carcinoma (RCC) overall and clear cell and papillary histological subtypes in the NIH-AARP Diet and Health Study.

METHODS

Nitrate and nitrite intakes were estimated from a 124-item food frequency questionnaire. Over a mean follow-up of 9 years, we identified 1816 RCC cases (n=498, clear cell; n=115, papillary cell) among 491 841 participants. Cox proportional hazard regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

Individuals in the highest quintile of nitrite intake from animal sources compared with those in the lowest quintile, had an increased risk of total RCC and clear cell subtype (HR=1.28, 95% CI, 1.10-1.49 and HR=1.68, 95% CI, 1.25-2.27, respectively). Nitrite from processed meats and other animal sources were associated with increased clear cell adenocarcinoma risk (HR=1.33, 95% CI, 1.01-1.76 and HR=1.78, 95% CI, 1.34-2.36, respectively). We found no association for nitrite intake from plant sources or nitrate intake overall.

CONCLUSION

Our findings suggest that nitrite from animal sources may increase the risk of RCC, particularly clear cell adenocarcinomas.

Meat-related compounds and colorectal cancer risk by anatomical subsite

Since meat may be involved in the etiology of colorectal cancer, associations between meat-related compounds were examined to elucidate underlying mechanisms in a population-based case-control study. Participants (989 cases/1,033 healthy controls) completed a food frequency questionnaire with a meat-specific module. Multivariable logistic regression was used to examine associations between meat variables and colorectal cancer; polytomous logistic regression was used for subsite-specific analyses. The following significant positive associations were observed for meat-related compounds: 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) and colorectal, distal colon, and rectal tumors; 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and colorectal and colon cancer tumors; nitrites/nitrates and proximal colon cancer; 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and rectal cancer; and benzo[a]pyrene and rectal cancer (P-trends < 0.05). For analyses by meat type, cooking method, and doneness preference, positive associations between red processed meat and proximal colon cancer and pan-fried red meat and colorectal cancer were found (P-trends < 0.05). Inverse associations were observed between unprocessed poultry and colorectal, colon, proximal colon, and rectal tumors; grilled/barbequed poultry and proximal colon cancer; and well-done/charred poultry and colorectal, colon, and proximal colon tumors (P-trends < 0.05). HCAs, PAHs, nitrites, and nitrates may be involved in colorectal cancer etiology. Further examination into the unexpected inverse associations between poultry and colorectal cancer is warranted.

Using gene-environment interaction analyses to clarify the role of well-done meat and heterocyclic amine exposure in the etiology of colorectal polyps

BACKGROUND

The role of well-done meat intake and meat-derived mutagen heterocyclic amine (HCA) exposure in the risk of colorectal neoplasm has been suggested but not yet established.

OBJECTIVE

With the use of gene-environment interaction analyses, we sought to clarify the association of HCA exposure with colorectal polyp risk.

DESIGN

In a case-control study including 2057 colorectal polyp patients and 3329 controls, we evaluated 16 functional genetic variants to construct an HCA-metabolizing score. To derive dietary HCA-exposure amount, data were collected regarding dietary intake of meat by cooking method and degree of doneness.

RESULTS

A 2-fold elevated risk associated with high red meat intake was found for colorectal polyps or adenomas in subjects with a high HCA-metabolizing risk score, whereas the risk was 1.3- to 1.4-fold among those with a low risk score (P-interaction ≤ 0.05). The interaction was stronger for the risk of advanced or multiple adenomas, in which an OR of 2.8 (95% CI: 1.8, 4.6) was observed for those with both a high HCA-risk score and high red meat intake (P-interaction = 0.01). No statistically significant interaction was found in analyses that used specific HCA exposure derived from dietary data.

CONCLUSION

High red meat intake is associated with an elevated risk of colorectal polyps, and this association may be synergistically modified by genetic factors involved in HCA metabolism.

Red meat and poultry, cooking practices, genetic susceptibility and risk of prostate cancer: results from a multiethnic case-control study

Red meat, processed and unprocessed, has been considered a potential prostate cancer (PCA) risk factor; epidemiological evidence, however, is inconclusive. An association between meat intake and PCA may be due to potent chemical carcinogens that are generated when meats are cooked at high temperatures. We investigated the association between red meat and poultry intake and localized and advanced PCA taking into account cooking practices and polymorphisms in enzymes that metabolize carcinogens that accumulate in cooked meats. We analyzed data for 1096 controls, 717 localized and 1140 advanced cases from the California Collaborative Prostate Cancer Study, a multiethnic, population-based case-control study. We examined nutrient density-adjusted intake of red meat and poultry and tested for effect modification by 12 SNPs and 2 copy number variants in 10 carcinogen metabolism genes: GSTP1, PTGS2, CYP1A2, CYP2E1, EPHX1, CYP1B1, UGT1A6, NAT2, GSTM1 and GSTT1. We observed a positive association between risk of advanced PCA and high intake of red meat cooked at high temperatures (trend P = 0.026), cooked by pan-frying (trend P = 0.035), and cooked until well-done (trend P = 0.013). An inverse association was observed for baked poultry and advanced PCA risk (trend P = 0.023). A gene-by-diet interaction was observed between an SNP in the PTGS2 gene and the estimated levels of meat mutagens (interaction P = 0.008). Our results support a role for carcinogens that accumulate in meats cooked at high temperatures as potential PCA risk factors, and may support a role for heterocyclic amines (HCAs) in PCA etiology.

Meat intake and risk of non-Hodgkin lymphoma

We conducted a population-based, case-control study to test the hypothesis that consumption of meat and meat-related mutagens increases the risk of non-Hodgkin lymphoma (NHL), and whether the associations are modified by N-acetyltransferase (NAT) 1 and 2. Participants (336 cases and 460 controls) completed a 117-item food frequency questionnaire. The risk of NHL was associated with a higher intake of red meat (OR = 1.5; CI, 1.1-2.2), total fat (OR = 1.4; CI, 1.0-2.1), and oleic acid (OR = 1.5; CI, 1.0-2.2). NHL risk was also associated with a higher intake of very well-done pork (OR = 2.5; 95 % CI, 1.4-4.3) and the meat-related mutagen MeIQx (OR = 1.6; 95 % CI, 1.1-2.3). Analyses of the major NHL histologic subtypes showed a positive association between diffuse large B cell lymphoma (DLBCL) and higher intake of red meat (OR = 2.1; 95 % CI, 1.1-3.9) and the association was largely due to meat-related mutagens as a positive association was observed for higher intakes of both MeIQx (OR = 2.4; 95 % CI, 1.2-4.6) and DiMeIQx (OR = 1.9; 95 % CI, 1.0-3.5). Although the OR for follicular lymphoma (FL) was also increased with a higher red meat intake (OR = 1.9; 95 % CI, 1.1-3.3), the association appeared to be due to increased oleic acid (OR = 1.7; 95 % CI: 0.9-3.1). We found no evidence that polymorphisms in NAT1 or NAT2 modify the association between NHL and meat-related mutagens. Our results provide further evidence that red meat consumption is associated with an increase in NHL risk, and new evidence that the specific components of meat, namely fat and meat-related mutagens, may be impacting NHL subtype risk differently.

Comparability and repeatability of methods for estimating the dietary intake of the heterocyclic amine contaminant 2-amino-1-methyl-6-phenylimidazo[4,5b]pyridine (PhIP)

Inconsistent risk estimates for dietary heterocyclic amine (HCA) exposure and cancers may be due to differences in exposure assessment methods and the associated measurement error. We evaluated repeatability and comparability of intake estimates of the HCA 2-amino-1-methyl-6-phenylimidazo[4,5b]pyridine (PhIP) among two food frequency questionnaire (FFQ) collections, three diary collections, and three measurements of urinary PhIP and its metabolites in 36 non-smokers in Baltimore, Maryland, during 2004-2005. Collections spanned ∼9 months. Method repeatability was characterised with intraclass correlation coefficients (ICCs). Comparability among methods was assessed with Spearman correlation coefficients. Within-subject variability in PhIP intake was comparably high across all methods (ICCs of 0.20, 0.30, and 0.15 for FFQ, diary, and creatinine-adjusted urinary PhIP, respectively). Mean diary-based PhIP intake and mean urinary PhIP concentration were strongly correlated when restricting the analysis to participants with at least one non-zero diary-based estimate of PhIP intake (n = 15, r = 0.75, p = 0.001), but not in the full study population (n = 36, r = 0.18, p = 0.28). Mean PhIP intake from the FFQ was not associated with that either based on the diary or urinary PhIP separately, but was modestly correlated with a metric that combined the diary- and biomarker-based approaches (r = 0.30, p = 0.08). The high within-subject variability will result in significantly attenuated associations if a single measure is used to estimate exposure within an epidemiologic study. Improved HCA assessment tools, such as a combination of methods or validated biomarkers that capture long term exposure, are needed.

Polymorphisms in carcinogen metabolism enzymes, fish intake, and risk of prostate cancer

Cooking fish at high temperature can produce potent carcinogens such as heterocyclic amines and polycyclic aromatic hydrocarbons. The effects of these carcinogens may undergo modification by the enzymes responsible for their detoxification and/or activation. In this study, we investigated genetic polymorphisms in nine carcinogen metabolism enzymes and their modifying effects on the association between white or dark fish consumption and prostate cancer (PCA) risk. We genotyped 497 localized and 936 advanced PCA cases and 760 controls from the California Collaborative Case-Control Study of Prostate Cancer. Three polymorphisms, EPHX1 Tyr113His, CYP1B1 Leu432Val and GSTT1 null/present, were associated with localized PCA risk. The PTGS2 765 G/C polymorphism modified the association between white fish consumption and advanced PCA risk (interaction P 5 0.002), with high white fish consumption being positively associated with risk only among carriers of the C allele. This effect modification by PTGS2 genotype was stronger when restricted to consumption of well-done white fish (interaction P 5 0.021). These findings support the hypotheses that changes in white fish brought upon by high-temperature cooking methods, such as carcinogen accumulation and/or fatty acid composition changes, may contribute to prostate carcinogenesis. However, the gene-diet interactions should be interpreted with caution given the limited sample size. Thus, our findings require further validation with additional studies.

Meat intake is not associated with risk of non-Hodgkin lymphoma in a large prospective cohort of U.S. men and women

Meat intake has been inconsistently associated with risk of non-Hodgkin lymphoma (NHL), a heterogeneous group of malignancies of the lymphoid tissue etiologically linked to immunomodulatory factors. In a large U.S. cohort, we prospectively investigated several biologically plausible mechanisms related to meat intake, including meat-cooking and meat-processing compounds, in relation to NHL risk by histologic subtype. At baseline (1995-1996), participants of the NIH-AARP Diet and Health Study completed a diet and lifestyle questionnaire (n = 492,186), and a subcohort (n = 302,162) also completed a questionnaire on meat-cooking methods and doneness levels. Over a mean of 9 y of follow-up, we identified 3611 incident cases of NHL. In multivariable Cox proportional hazards regression models, we found no association between intake of red meat, processed meat, fish, poultry, heme iron, nitrite, nitrate, animal fat, or protein and NHL risk. MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline) and DiMeIQx (2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline), heterocyclic amines formed in meats cooked to well done at high temperatures, were inversely associated with chronic lymphocytic leukemia/small lymphocytic lymphoma [n = 979; HR (95% CI) for the highest vs. lowest quintile of intake: 0.73 (0.55, 0.96) and 0.77 (0.61, 0.98), respectively]. In this large U.S. cohort, meat intake was not associated with NHL or any histologic subtypes of NHL. Contrary to findings in animal models and other cancer sites, meat-cooking and -processing compounds did not increase NHL risk.