Diet and breast cancer: studies in laboratory animals

Effects of Rich-in-Fat Diets and Highly Selective COX-2 Inhibitors on 7,12-Dimethylbenz-(A)-Anthracene-Induced Tumor Growth

The effects of diet, of non-steroidal anti-inflammatory drugs, or of their combination on carcinogenesis continue to be a case for controversy. Diets that are high in fat have been linked to increased risk of various tumors. At the same time there is substantial, but not conclusive, evidence that the risk of breast and colon cancer correlates with total fat intake rather than a specific type of fat. On the other hand, non-steroidal anti-inflammatory drugs (NSAIDs) have been studied extensively because they appear to delay or inhibit the development of malignant and pre-malignant lesions. 7,12-Dimethylbenz-(a)-anthracene (DMBA) has been used for a long time to induce carcinogenesis in a number of rat animal models. The present study attempts to identify the effects on DMBA-induced tumor growth (a) of diets rich in fat and (b) of the highly selective COX-2 inhibitor Celecoxib, which has been claimed to offer substantial protection against carcinogenesis.

Effects of different dietary fatty acids on the fatty acid compositions and the expression of lipid metabolic-related genes in mammary tumor tissues of rats

In this study, the effects of dietary fatty acids on the fatty acid compositions and lipid metabolic-related genes expression in N-methyl-N-nitrosourea (MNU)-induced rat mammary carcinogenesis were evaluated. The 50-day-old female Sprague-Dawley rats were intervened by different dietary fats (15% wt/wt), including saturated fatty acid (SFA), monounsaturated fatty acid (MUFA), n-6 polyunsaturated fatty acid (PUFA), n-3 PUFA, 1:1 n-6/n-3, 5:1 n-6/n-3, 10:1 n-6/n-3, and 1:2:1 S/M/P (1:1 n-6/n-3), alone or in combination with MNU. There was no mammary tumor occurrence in the control and MNU-treated n-3 PUFA groups after 18 wk. n-3 PUFA diet retarded the weight growth of rats. 1:1 n-6/n-3 diet significantly reduced the MNU-induced tumor incidence and tumor multiplicity compared with SFA, MUFA, n-6 PUFA, 5:1 n-6/n-3, 10:1 n-6/n-3 and 1:2:1 S/M/P diets (42.86% vs. 83.33%-92.31%, 0.79 vs. 2.62-2.85, P < 0.01). Additionally, 1:1 n-6/n-3 diet substantially increased cis-5,8,11,14,17-eicosapentaenoic acid and cis-4,7,10,13,16,19-docosahexaenoic acid levels, whereas it decreased C20:4 level and the mRNA expressions of fatty acid synthase, Cyclooxygenase-2 (COX-2), and 5-lipoxygenase (5-LOX) in mammary tissues (P < 0.05). These results suggest that 1:1 n-6/n-3 in the diet is effective in the prevention of mammary tumor development by increasing the n-3 PUFA content and reducing the expression of lipid metabolic-related genes.

Nutritional factors in relation to endometrial cancer: a report from a population-based case-control study in Shanghai, China

We evaluated the role of dietary nutrients in the etiology of endometrial cancer in a population-based case-control study of 1,204 newly diagnosed endometrial cancer cases and 1,212 age frequency-matched controls. Information on usual dietary habits was collected during an in-person interview using a validated, quantitative food frequency questionnaire. Logistic regression analysis was conducted to evaluate the association of nutrients with endometrial cancer risk using an energy density method (e.g., nutrient intake/1,000 kilocalories of intake). Higher energy intake was associated with increased risk, which was attributable to animal source energy and a high proportion of energy from protein and fat. Odds ratios comparing highest versus lowest quintiles of intake were elevated for intake of animal protein (Odds ratio (OR) = 2.0, 95% confidential interval: 1.5-2.7) and fat (OR = 1.5, 1.2-2.0), but reduced for plant sources of these nutrients (OR = 0.7, 0.5-0.9 for protein and OR = 0.6, 0.5-0.8 for fat). Further analysis showed that saturated and monounsaturated fat intake was associated with elevated risk, while polyunsaturated fat intake was unrelated to risk. Dietary retinol, beta-carotene, vitamin C, vitamin E, fiber, and vitamin supplements were inversely associated with risk. No significant association was observed for dietary vitamin B1 or vitamin B2. Our findings suggest that associations of dietary macronutrients with endometrial cancer risk may depend on their sources, with intake of animal origin nutrients being related to higher risk and intake of plant origin nutrients related to lower risk. Dietary fiber, retinol, beta-carotene, vitamin C, vitamin E, and vitamin supplementation may decrease the risk of endometrial cancer.

Lipídio: fator de risco e prevenção do câncer de mama

A hipótese de que uma dieta rica em gordura promova o desenvolvimento do câncer de mama na menopausa é fortalecida por estudos caso-controle, que mostram forte associação positiva entre uma dieta rica em lipídios e as taxas de incidência de câncer de mama. Por outro lado, a ingestão dietética de gordura não parece estar relacionada com o risco de câncer de mama em estudos de coorte. Em vista desses achados conflitantes, tem sido difícil propor qualquer recomendação nutricional para a prevenção do câncer de mama. Estudos com animais e observações recentes em humanos, entretanto, têm mostrado evidências de que a dieta rica em ácido graxo linoléico estimula vários estágios no desenvolvimento de câncer mamário. Alguns estudos ainda mostram que o óleo de peixe, constituído de ácidos graxos ômega-3, parece prevenir o câncer pela influência sobre a atividade de enzimas e proteínas relacionadas à proliferação celular. Assim, são necessários estudos epidemiológicos que integrem as interações de ácidos graxos específicos com o catabolismo hormonal, fatores nutricionais protetores e de risco relacionados com o câncer de mama. Nesse trabalho, abordaremos os fatores protetores, de risco e as implicações quali e quantitativas dos ácidos graxos da dieta sobre o câncer de mama.

Dietary intakes of fat and fatty acids and risk of breast cancer: a prospective study in Japan

To examine the possible association of dietary fat and fatty acids with breast cancer risk in a population with a low total fat intake and a high consumption of fish, we analyzed data from the Japan Collaborative Cohort (JACC) Study. From 1988 to 1990, 26 291 women aged 40-79 years completed a questionnaire on dietary and other factors. Intakes of fat or fatty acids were estimated by using a food frequency questionnaire. Rate ratios (RR) were computed by fitting proportional hazards models. During the mean follow-up of 7.6 years, 129 breast cancer cases were documented. We found no clear association of total fat intake with breast cancer risk; the multivariate-adjusted RR across quartiles were 1.00, 1.29, 0.95, and 0.80 (95% confidence interval [CI] 0.46-1.38). A significant decrease in the risk was detected for the highest quartile of intake compared with the lowest for fish fat and long-chain n-3 fatty acids; the RR were 0.56 (95% CI 0.33-0.94) and 0.50 (0.30-0.85), respectively. A decreasing trend in risk was also suggested with an increasing intake of saturated fatty acids (trend P = 0.066). Among postmenopausal women at baseline, the highest quartile of vegetable fat intake was associated with a 2.08-fold increase in risk (95% CI 1.05-4.13). This prospective study did not support any increase in the risk of breast cancer associated with total or saturated fat intake, but it suggested the protective effects of the long-chain n-3 fatty acids that are abundant in fish.

The meaning of food to breast cancer survivors

Although a definitive relationship between diet and breast cancer remains controversial, many women adopt dietary change after diagnosis. To understand factors motivating dietary change, we explored the meanings that breast cancer survivors attached to food during recovery. Six women who were breast cancer survivors for six to 19 years participated in semi-structured interviews exploring personal meanings attached to food, dietary changes after diagnosis, factors influencing dietary change, and experiences with food in relation to breast cancer. Two distinct phases emerged. These corresponded to active treatment, when women used food to gain control, to cope, for comfort, and for hope, and to post-treatment, when the meanings that women attached to food were shaped by the perception of food's role in breast cancer causation. Women who believed that diet prevents a first diagnosis adopted change to prevent recurrence, while those who did not believe in the relationship between diet and breast cancer adopted change to improve health. In women with breast cancer, food can be an important coping mechanism. Women may benefit from counselling grounded in the meanings they attach to food over the recovery continuum.

Biomarkers of dietary fatty acid intake and the risk of breast cancer: a meta-analysis

The use of the fatty acid composition of adipose tissue, erythrocyte membranes, serum and plasma as biological markers of fatty acid intake was recently introduced in epidemiological studies. The biomarkers of fatty acid intake have the advantage of providing quantitative measurement independent of energy intake and of the subject's memory. We performed a meta-analysis of published results of epidemiological studies of the composition of fatty acids in biological samples and breast cancer risk. The analysis was based on 3 cohort and 7 case-control studies including 2,031 cases and 2,334 controls. The summary statistic used was the average of the relative risk estimated for each level of the fatty acid on study, weighted by the inverse of its variance. Random effect models were assumed when the test for heterogeneity was significant. Overall relative risks were estimated for studies including pre- and post-menopausal breast cancer and separately for post-menopausal women. In cohort studies, a significant protective effect was found for total n-3 polyunsaturated fatty acids, while total monounsaturated fatty acids, oleic acid (C18:1 n-9c) and palmitic acid (C16:0) were significantly associated with an increase of breast cancer risk. Total saturated fatty acids were significantly associated with breast cancer risk in cohort studies only in postmenopausal women. For case-control studies, the only finding was for alpha linolenic acid (C18:3, n-3), which showed an inverse association bordering on statistical significance. The findings of cohort studies fit well with hypotheses derived from experimental animal studies. More epidemiological cohort studies that integrate biological markers of dietary fatty acid intake are needed in order to determine the contribution of different types of fatty acids in the etiology of breast cancer.

Dietary factors affecting uterine weights of immature CD-1 mice used in uterotrophic bioassays

A study was conducted to determine the effects of dietary factors in natural ingredient and purified diets on uterine weights of immature CD-1 mice used in uterotrophic bioassays. Factors evaluated included body weight gain, dietary phytoestrogen content, total metabolizable energy, and percent crude fiber. Fifteen to 147 mice per group, housed 5 per cage, were randomly assigned to each of the 20 test diets. The test diets were fed for 7 days to 15-day old immature female CD-1 mice and their body weight gain and uterine weights were determined. Analysis of covariance procedures were used to evaluate differences in uterine weights, after adjusting for body weight and time-related trends. Fisher's least significant difference test was used to compare adjusted uterine weights and weight gains among the test diets. Additionally, multiple linear regression procedures were used to identify those characteristics of the rodent diet that were most predictive of the adjusted uterine weights. Total metabolizable energy was significantly (P < 0.01) correlated with and was predictive of uterine weights. The following dietary variables were not significantly predictive of uterine weights: total daidzein and genistein content, percent protein, fat, N-FE (carbohydrates) or percent crude fiber. We concluded that: (1) total metabolizable energy (ME) in natural ingredient or purified diets has a significant (P < 0.01) effect on the uterine weights of immature mice used in 7-day uterotrophic bioassays; (2) a standardized, estrogen-free diet with a constant level of ME should be used for conducting uterotrophic assays when comparing results between different laboratories or when determining the estrogenic or anti-estrogenic activity of endocrine disruptor compounds; (3) the mouse uterotrophic assay remains a sensitive bioassay for assessing chemicals for estrogenic activity or for the detection of total estrogenic activity in rodent diets that may be contaminated with estrogenic compounds, and (4) chemical assays should be used to detect or measure low levels of the phytoestrogens in rodent diets.

Effects of dietary fat on virus-induced pancreatic carcinogenesis in guinea fowl

The present study was performed to assess the effects of diets supplemented with low (5%) and high (20%) corn oil on a Pts 56 retrovirus-induced model of pancreatic carcinogenesis in guinea fowl. The early microscopic lesions appear after 3 mo after virus treatment and progress over time. Eight to 10 mo after initiation, up to 100% of virus-inoculated birds develop multiple hyperplastic and neoplastic pancreatic lesions of duct/ductular phenotype. Short-term (1-4 mo) feeding of low- or high-fat diets, beginning at Month 3, had no significant effects on body and pancreatic weight. However, the incidence, multiplicity, and areas of the pancreatic tissue occupied by intra- and interlobular aggregates of hyperplastic ducts with mucinous metaplasia of the lining cells were significantly increased compared with the birds fed the common diet. At the same time, development of ductular neoplasms, particularly carcinomas, was retarded compared with the common diet-fed controls. Long-term (5-7 mo) fat intake resulted in an increase in body weight gain, while absolute pancreatic weights remained relatively constant. Furthermore, the high- and low-fat diets caused a significant increase in areas of retrovirus-induced pancreatic lesions, as well as an increase in multiplicity of ductular neoplasms compared with short-term fat feeding. It is concluded that short-term feeding of diets supplemented with 5% or 20% corn oil delayed the development of the common virus-induced ductular neoplasms, particularly carcinomas, and had an enhancing effect on development of hyperplastic inter- and intralobular aggregates of ducts. This finding was not observed, however, during the long-term feeding period of the study.

Changes in sex hormone-binding globulin, insulin, and serum lipids in postmenopausal women on a low-fat, high-fiber diet combined with exercise

Dietary factors including fat and fiber have been reported to play a role in the development of breast cancer, possibly mediated by changes in estradiol. Diet and exercise have been shown to affect levels of sex hormone-binding globulin (SHBG), which in turn regulate the bioavailability of estradiol. Diet and exercise also affect insulin levels, which play a role in the synthesis of SHBG, and the hormone itself is a potent mitogen for many cancer cell lines. This study was designed to measure the effects of a low-fat, high-fiber diet, combined with regular aerobic exercise, on the levels of SHBG, insulin, and serum lipids in postmenopausal women with or without hormone replacement therapy (HRT). Two groups of postmenopausal women, 11 on HRT and 11 not on HRT, underwent a low-fat (1O% fat calories), high-fiber (65-70 g/day) diet-and-exercise intervention for three weeks. Serum SHBG, insulin, and lipids were measured before and after the regimen. After the intervention, SHBG levels were significantly increased for the women on HRT (44.5 +/- 3.4 vs. 62 +/- 6.4 nmol/l) and the women not on HRT (32.1 +/- 4.6 vs. 45.5 +/- 6.1 nmol/l, both changes p < 0.01). Also after the intervention, insulin levels were significantly reduced for the women on HRT (196 +/- 44.4 vs. 119.8 +/- 28.7 pmol/l) and the women not on HRT (144.2 +/- 17.9 vs. 115.5 +/- 20.8 pmol/l, both changes p < 0.01). Body mass index and total cholesterol were significantly reduced for both groups of women (all changes p < 0.01). Although the exact mechanism for the change in SHBG is not known, the increases in SHBG and reductions in insulin as a result of this lifestyle intervention should reduce the risk for breast cancer in postmenopausal women.

Post-initiation treatment of Indole-3-carbinol did not suppress N-methyl-N-nitrosourea induced mammary carcinogenesis in rats

The consumption of cruciferous vegetables (the Family of Cruciferae) such as cabbage, broccoli and Brussels sprouts has been shown to have cancer chemopreventive effects in humans and experimental animals. Indole-3-carbinol (I3C), one component of cruciferous vegetables, has been shown to exert cancer chemopreventive influence in liver, colon, and mammary tissue when given before or concurrent with exposure to a carcinogen. However in some reports, there has been evidence that consumption of I3C after carcinogen treatment might be associated with tumor promotion in some tissues. There have been no reports, to our knowledge, of post-initiation effects of I3C in the N-methyl-N-nitrosourea (MNU)-induced mammary tumor model in rats. Our studies were performed to examine this question. Ninety-six, 4-week-old female Sprague-Dawley rats were randomly divided into five groups. The animals of groups 1, 2 and 3 received an intraperitoneal injection of MNU at the age of 50 days. The animals of groups 4 and 5 were injected with saline only at the same time. Animals of groups 1 and 2 were given diet containing 100 ppm and 300 ppm I3C from week 1 until week 25 after MNU treatment. The animals of group 4 were given basal diet containing 300 ppm I3C without MNU treatment. All animals were killed at week 25. The incidences of mammary tumors in the groups 1, 2 and 3 were 95.8% (23/24), 83.3% (20/24) and 82.4% (28/34), respectively. The average number of tumors in the tumor bearing rats of the MNU and I3C 300 ppm group (group 2; 3.85+/-0.63) was higher than that in the MNU alone group (group 3; 2.46+/-0.31). These results represented that exposure to I3C after carcinogen treatment did not suppress development of mammary tumors.

Height, weight, weight change and risk of breast cancer in Rio de Janeiro, Brazil

CONTEXT

The relationship between body size and breast cancer still remains controversial in considering menopausal status.

OBJECTIVE

To evaluate the association of height, weight and weight changes with breast cancer in the city of Rio de Janeiro, Brazil.

DESIGN

Case-control study.

SETTING

National Cancer Institute (INCA), Rio de Janeiro, Brazil, and State University of Rio de Janeiro (UERJ).

SAMPLE

177 incident cases of invasive breast cancer admitted to the main hospital of INCA between May 1995 and February 1996, and 377 controls recruited from among female visitors to the same hospital.

MAIN MEASUREMENTS

Height and weight were measured and information on maximum weight, weight at ages 18 and 30 years, and potential risk factors were ascertained by interview at the hospital.

RESULTS

Height was not related to risk of breast cancer among both pre and postmenopausal women. Nevertheless, women in this study were shorter than in studies that have found a positive association. Premenopausal women in the upper quartile of recent body mass index (BMI) and maximum BMI showed a reduced risk of breast cancer (P for trend < or = 0.03). Weight loss between ages 18 and 30 years and from 18 years to present was also associated with breast cancer among premenopausal women.

CONCLUSIONS

These findings may merely indicate the known association between leanness and breast cancer. Further studies should explore the role of weight loss on breast cancer risk.

Study design and hypothesis testing: issues in the evaluation of evidence from research in nutritional epidemiology

In addressing questions about the relations of dietary factors to disease in human populations, epidemiologic studies must account for the complexity of dietary habits, the intercorrelations among dietary habits, and the correlations of those habits with other behaviors. Furthermore, for studies of chronic disease, relevant dietary exposures may occur over decades. The classic epidemiologic study designs have been used to examine the associations between diet and disease; the strengths and weaknesses of those designs must be considered. Concerns have been raised regarding the validity of the measures of diet, the differential recall of diet by diseased individuals in case-control studies, and confounding by other related factors in both case-control and cohort studies. In clinical trials there may be difficulties in effecting the necessary dietary changes, especially for macronutrients, and there are also concerns about those circumstances in which participants cannot be blinded to their treatment. For case-control and cohort studies and for some clinical trials, intercorrelations among nutrients are a concern in the identification of factors that are important in the etiology of disease. It is important to understand these considerations when interpreting nutritional epidemiologic studies for the purpose of setting public policy. No one study can be considered definitive in the understanding of a diet-disease relation. However, epidemiologic findings from multiple studies taken together can contribute significantly to our understanding of diet in relation to disease in humans.

Diet and mammary gland carcinogenesis

The variation in human breast cancer incidence rates worldwide suggests that lifestyle factors, especially diet, influence breast cancer risk. There is convincing evidence that diets associated with rapid growth and greater adult height increase breast cancer risk. In addition, diet and other lifestyle factors which lead to high body mass, especially during postmenopausal years, also appear to increase risk. Several dietary components have been evaluated in epidemiological and animal studies for their role in breast cancer. Dietary fat was once implicated in the high incidence of breast cancer in the Western world, but its role in breast cancer is now controversial. In contrast, alcohol consumption is currently recognized as the best-established dietary risk factor in this disease. Carcinogens that cause mammary gland cancer in rats such as heterocyclic amines and polycyclic aromatic hydrocarbons are found in cooked meat, but it is not yet known if these carcinogens are etiological factors in human breast cancer. Fruits and vegetables are rich in potential chemopreventive factors that may lower breast cancer risk. Practical approaches to dietary modification that include increasing fruit and vegetable consumption, eating a low fat diet, reducing cooked meat consumption, and avoiding alcohol are likely to be of potential overall benefit in lowering the risk of human breast cancer.

Considerations in the design of studies of dietary influences on mammary carcinogenesis in rats and mice

Design of diets for the study of dietary influences in mammary gland carcinogenesis requires attention to several questions: (1) Do the diets satisfy the nutritional needs of the animal under the conditions of the experiment, and are they palatable? (2) Does the protocol include determination of feed intake (if indicated) and of achievement of the desired level of nutrient deficiency, adequacy, or excess? (3) Are there potentially confounding nutrient interactions or nutrient effects or physiological or pathological responses that must be considered? The particular sensitivity of mammary gland tumorigenesis to intake of fat and calories and to body weight gain must be considered and controlled for in all experiments.