Carbon and nitrogen stable isotopic composition of hair protein and amino acids can be used as biomarkers for animal-derived dietary protein intake in humans

From Local Farms to Supermarket Foods: The Story of the Homogenization of the Argentine Diet Told by the Isotope Ratios of Modern Teeth

OBJECTIVES

Nutritional changes over the last century, driven by globalization, hypermarketization, and malnutrition, are global in scale. Large countries in the Global South might be resilient to dietary homogenization due to their natural diversity of regions and ecosystems, which might have prevented the adoption of supermarket diets. Argentina has a wide array of ecosystems and historically different subsistence diets dependent on regional characteristics. We analyzed the spatiotemporal variation of stable isotope values in Argentina using modern teeth to test for regional dietary patterns and its consistence over time.

MATERIALS AND METHODS

We collected teeth from voluntary donors born between 1940 and 2010, from 72 locations across Argentina. A total of 119 teeth were analyzed for the markers δ 13Cdentine, δ 13Cenamel, δ 15N, and δ 34S. A reconstruction of isotopic niches was performed to estimate dietary patterns across different regions and time periods.

RESULTS

This study is the first to analyze changes in modern dietary patterns in Argentina using isotopic data measured in contemporary teeth. We showed latitudinal, longitudinal, and temporal differences in isotopic values, reflecting the variation in available resources within the country. Changes in the diet were observed over time, including declining δ 15N values, a reduction in δ 34S range, and a trend toward homogenization of δ 13Cenamel values. Conversely, δ 13Cdentine values remained constant over time, maintaining latitudinal patterns and regional differences across regions.

DISCUSSION

This study increases our understanding of modern population dietary patterns both spatially and over the last 70 years. Our findings suggest that the Argentine population has shifted toward a supermarket diet in recent years.

Associations of Food Group Intakes with Serum Carbon Isotope Ratio Values in Youth: Results from 2 Prospective Pediatric Cohort Studies

BACKGROUND

The carbon isotope ratio (CIR) is a candidate biomarker for sugar-sweetened beverage (SSB) intake in the United States. However, research specific to youth, who differ in their physiology and dietary patterns compared with adults, is lacking.

OBJECTIVES

We evaluated longitudinal associations of SSB intakes across childhood/adolescence with serum CIR. We also explored the relationship between other dietary intakes and serum CIR.

METHODS

Data were from participants in two longitudinal, pediatric cohorts in Colorado: Exploring Perinatal Outcomes among CHildren (EPOCH) study (visits at median 10 and 16 y, n = 150) and Healthy Start Study (visits at median 5 and 9 y, n = 166). Serum CIR was measured using isotope ratio mass spectrometry. Diet was assessed by food-frequency questionnaires (EPOCH) or 24-h diet recalls (Healthy Start). We assessed associations of longitudinal dietary intakes (log2-transformed, standardized) with serum CIR using linear mixed models adjusted for age, sex, and energy intake, and associations of change values between visits using linear regression models.

RESULTS

In linear mixed models, higher SSB intake across visits was associated with higher serum CIR in both cohorts [β (95% confidence interval (CI)): 0.11 (0.06, 0.15) in EPOCH and 0.14 (0.07, 0.21) in Healthy Start]. Higher meat intake and a higher dietary animal protein ratio were also positively associated with serum CIR in both cohorts [β (95% CI): 0.08 (0.05, 0.12) and 0.18 (0.13, 0.23) in EPOCH; 0.08 (0.01, 0.16) and 0.28 (0.21, 0.35) in Healthy Start]. In change analyses, there were positive associations for changes in the dietary animal protein ratio between visits with changes in serum CIR in both cohorts, but not for changes in SSB intake.

CONCLUSIONS

Our findings support serum CIR as a potential biomarker of SSB intake in youth cross-sectionally; however, there was not a strong link between change values over longer-term follow-up. Meat/animal protein intake was also consistently and, at times, more strongly associated with serum CIR.

Metal concentrations in the whole blood of farmers in southeast Brazil

In this study, we measured Ni, Co, Cd, and Pb concentrations in the whole blood of farmers from southeast Brazil to address the factors influencing human exposure in this population. The factors included smoking, alcohol consumption, aging, body composition, gender, and feeding preferences, which were measured through carbon and nitrogen isotopic composition. We also calculated and compared the reference values (RVs) of the measured elements to evaluate ongoing exposure levels. We observed the influence of lifestyle habits on metal exposure; Cd levels were statistically higher in smokers, and alcohol consumption affected only Pb concentrations, with an association also observed with the frequency of alcohol ingestion. The metal levels were positively associated with both isotope values, indicating that feeding may be the dominant source of these elements in this population. We also observed the effect of endogenous sources measured through age, as increased Pb concentrations in both genders and higher Cd levels in older women, which is related to bone, kidney, and liver accumulation. The body mass index was negatively associated with Ni, Co, and Cd in women and positively in men. The negative associations may indicate that body fat may act as a reservoir for metals, reducing their availability in the blood in individuals with higher body mass and possibly influencing the assessment of exposure levels. The evaluated population presented elevated RVs for all elements: Ni 36, Co 3.3, Cd 16, and Pb 149 μg L-1. These values point to higher exposure in this population compared to other studies in Brazil and worldwide. These results emphasize an urgent need for monitoring programs for toxic substances in Brazil and evaluating possible health effects, given the ongoing environmental exposure associated with endogenous exposure and lifestyle habits that promote higher metal levels in this population.

Dietary habits of pastoralists on the Tibetan plateau are influenced by remoteness and economic status

In general, dietary habits of pastoralists are livestock-derived, but are also influenced by external food sources under globalization. We hypothesized that dietary habits of pastoralists would be influenced by their remoteness, and that changes from the traditional diet would result in deviations in the local ecological chain. To test this hypothesis, we determined the δ13C and δ15N values of soil, plants, and hair of animals and pastoralists (n = 885). The δ13C value in human hair reflects the proportions of protein originating from C3 and C4 plants; whereas, the δ15N value reflects the proportions of protein derived from plants and animals, with higher values indicating a greater consumption of meat. The isotopic signatures enabled us to estimate the variation in dietary habits of pastoralists across a socio-economic gradient of easily accessible to remote areas on the Tibetan plateau, and to determine the trophic transfer of the isotopes along an ecological chain. The trophic magnification factor (TMF) evaluated the trophic transfer of δ15N in the soil-plants-animals-pastoralists ecological chain. The high δ15N values in soil and plants were not recovered in animals and pastoralists in easily accessible and developed areas, indicating the use of external feed and food resources, and that they deviated from the ecological chain. The mean δ13C (-22.0 ‰) and δ15N values (6.9 ‰) of pastoralists indicated diets consisting mainly of local C3 plants and animal products. However, pastoralists in remote areas relied more on meat protein and on the local ecological chain than pastoralists in easily accessible areas, as their δ15N values and trophic magnification factor of δ15N in the ecological chain were greater. In addition to remoteness, per capita GDP influenced dietary changes in pastoralists, with richer pastoralists consuming more external food. We concluded that dietary changes of pastoralists in the easily accessible areas were due to external food resources and alterations in the local ecological chain of animals and plant-based foods available to the pastoralists.

A review on proteomic and genomic biomarkers for gelatin source authentication: Challenges and future outlook

Biomarkers are compounds that could be detected and used as indicators of normal and/or abnormal functioning of different biological systems, including animal tissues and food matrices. Gelatin products of animal origin, mainly bovine and porcine, are currently under scrutiny mainly due to the specific needs of some sectors of the population related to religious beliefs and their dietary prohibitions, as well as some potential health threats associated with these products. Thus, manufacturers are currently in need of a reliable, convenient, and easy procedure to discern and authenticate the origin of animal-based gelatins (bovine, porcine, chicken, or fish). This work aims to review current advances in the creation of reliable gelatin biomarkers for food authentication purposes based on proteomic and DNA biomarkers that could be applied in the food sector. Overall, the presence of specific proteins and peptides in gelatin can be chemically analysed (i.e., by chromatography, mass spectroscopy, electrophoresis, lateral flow devices, and enzyme-linked immunosorbent assay), and different polymerase chain reaction (PCR) methods have been applied for the detection of nucleic acid substances in gelatin. Altogether, despite the fact that numerous methods are currently being developed for the purpose of detecting gelatin biomarkers, their widespread application is highly dependent on the cost of the equipment and reagents as well as the ease of use of the various methods. Combining different methods and approaches targeting multiple biomarkers may be key for manufacturers to achieve reliable authentication of gelatin's origin.

The association between carbon and nitrogen stable isotope ratios of human hair and hypertension

BACKGROUND

The relationship between stable isotope ratios and dietary protein sources has been reported. However, few studies have examined the effect of stable isotope ratios on metabolic risk in humans. We investigated whether the stable isotope ratios of carbon and nitrogen in human hair are associated with blood pressure and hypertension.

METHODS

We conducted a cross-sectional study of 392 subjects (228 men and 164 women). Hair samples of the subjects were used for the measurement of stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N).

RESULTS

The δ¹³C and δ¹⁵N values showed positive correlations with diastolic blood pressure in the subjects without antihypertensive medication. In the subjects without antihypertensive medication, the multivariable-adjusted odds ratio (95% confidence interval) for hypertension was 1.55 (1.04-2.30) per 1‰ increase in δ¹⁵N and 1.22 (0.86-1.73) per 1‰ increase in δ¹³C, respectively. However, in the subjects with antihypertensive medication, neither δ¹³C nor δ¹⁵N values showed a significant association with hypertension.

CONCLUSIONS

The stable isotopic ratio of nitrogen in scalp hair is independently associated with hypertension in subjects without antihypertensive medication. The hair δ¹⁵N value might be used as a surrogate marker to screen a high-risk population for hypertension.

A new technique to study nutrient flow in host-parasite systems by carbon stable isotope analysis of amino acids and glucose

Stable isotope analysis of individual compounds is emerging as a powerful tool to study nutrient origin and conversion in host-parasite systems. We measured the carbon isotope composition of amino acids and glucose in the cestode Schistocephalus solidus and in liver and muscle tissues of its second intermediate host, the three-spined stickleback (Gasterosteus aculeatus), over the course of 90 days in a controlled infection experiment. Similar linear regressions of δ¹³C values over time and low trophic fractionation of essential amino acids indicate that the parasite assimilates nutrients from sources closely connected to the liver metabolism of its host. Biosynthesis of glucose in the parasite might occur from the glucogenic precursors alanine, asparagine and glutamine and with an isotope fractionation of - 2 to - 3 ‰ from enzymatic reactions, while trophic fractionation of glycine, serine and threonine could be interpreted as extensive nutrient conversion to fuel parasitic growth through one-carbon metabolism. Trophic fractionation of amino acids between sticklebacks and their diets was slightly increased in infected compared to uninfected individuals, which could be caused by increased (immune-) metabolic activities due to parasitic infection. Our results show that compound-specific stable isotope analysis has unique opportunities to study host and parasite physiology.

Amino Acid Nitrogen Isotope Ratios Respond to Fish and Meat Intake in a 12-Week Inpatient Feeding Study of Men

BACKGROUND

The natural abundance nitrogen stable isotope ratio (NIR) of whole tissue correlates with animal protein intakes, including meat and fish. Amino acid (AA) NIRs (NIRAAs) are more variable than the whole-tissue NIRs and may thus better differentiate among foods.

OBJECTIVES

We evaluated whether NIRAAs were associated with intakes of fish and meat and whether these dietary associations were larger than with whole-tissue NIRs.

METHODS

Men were recruited at the National Institute of Diabetes and Digestive and Kidney Diseases in Phoenix, Arizona, and randomly assigned to one of eight 12-wk inpatient dietary interventions, which varied the presence/absence of fish, meat, and sugar-sweetened beverages (SSBs) in all possible combinations. Fasting blood was drawn pre- and postintervention and plasma and RBC NIRAAs (free and protein-bound) were measured as secondary outcomes in 32 participants. Multivariable regression was used to determine responses of postintervention NIRAAs to dietary variables, and logistic regression was used to calculate receiver operating characteristic AUCs.

RESULTS

Most plasma NIRAAs increased with fish and meat intakes, but to a greater extent with fish intake. The largest increase in response to fish intake was plasma NIRLeucine (β = 2.19, SE = 0.26). The NIRThreonine decreased with both fish and meat intakes. Fewer RBC NIRAAs increased with fish intake, and only RBC NIRProline increased with meat intake. No plasma or RBC NIRAA responded to SSB intake. We identified fish intake with a high degree of accuracy using plasma NIRLeucine (corrected AUC, cAUC = 0.96) and NIRGlutamic acid/glutamine (cAUC = 0.93), and meat intake to a lower degree using plasma NIRProline (cAUC = 0.80) and RBC NIRProline (cAUC = 0.85).

CONCLUSIONS

Plasma and RBC NIRAAs were associated with fish and meat intakes but were not superior to whole-tissue stable isotope biomarkers in identifying these intakes in a US diet. This trial is registered at www.clinicaltrials.gov as NCT01237093.

An evaluation of the serum carbon isotope ratio as a candidate predictive biomarker of the dietary animal protein ratio (animal protein/total protein) in a 15-day controlled feeding study of US adults

BACKGROUND

The serum natural abundance carbon isotope ratio (CIR) was recently identified as a candidate biomarker of animal protein intake in postmenopausal women. Such a biomarker would help clarify the relation between dietary protein source (plant or animal) and chronic disease risk.

OBJECTIVES

We aimed to evaluate the performance of the serum CIR as a biomarker of dietary protein source in a controlled feeding study of men and women of diverse age and BMI.

METHODS

We conducted a 15-d feeding study of 100 adults (age: 18-70 y, 55% women) in Phoenix, AZ. Participants were provided individualized diets that approximated habitual food intakes. Serum was collected at the end of the feeding period for biomarker measurements.

RESULTS

Median [IQR] animal protein intake was 67 g/d [55-88 g/d], which was 64% of total protein. The serum CIR was positively correlated with animal protein and inversely correlated with plant protein intake, leading to a strong correlation (r2 = 0.76) with the dietary animal protein ratio (APR; animal/total protein). Regressing serum CIR on the APR, serum nitrogen isotope ratio (NIR), gender, age, and body weight generated an R2 of 0.78. Following the measurement error model for predictive biomarkers, the resulting regression equation was then inverted to develop a calibrated biomarker equation for APR. Added sugars ratio (added/total sugars intake) and corn intakes also influenced the serum CIR but to a much lesser degree than the APR; variations in these intakes had only small effects on biomarker-estimated APR.

CONCLUSIONS

Based on our findings in this US cohort of mixed sex and age, we propose the serum CIR alongside NIR as a predictive dietary biomarker of the APR. We anticipate using this biomarker to generate calibrated estimates based on self-reported intake and ultimately to obtain more precise disease risk estimates according to dietary protein source.

Dietary homogenization and spatial distributions of carbon, nitrogen, and sulfur isotope ratios in human hair in South Korea

Dietary homogenization has progressed worldwide due to westernization and the globalization of food production systems. We investigated dietary heterogeneity in South Korea by examining the spatial distribution of carbon (C), nitrogen (N), and sulfur (S) isotope ratios using 264 human hair samples. Overall, variation in isotope values was small, indicating low dietary heterogeneity. We detected differences in δ13C, δ15N, and δ34S values between administrative provinces and metropolitan cities; inter-regional differences were typically < 1 ‰. Values of δ34S were significantly lower in hair samples from inland regions relative to those from coastal locations, and a similar pattern was observed in δ15N values. Understanding geographic variation in δ34S and δ15N values in human hair is useful for provenancing humans in South Korea.

Associations Between Sugars Intakes and Urinary Sugars Excretion and Carbon Stable Isotope Ratios in Red Blood Cells as Biomarkers of Sugars Intake in a Predominantly Māori Population

Determining the extent to which added sugars intake contribute to non-communicable disease in various populations is challenging because it is difficult to accurately measure intakes. Biomarkers may provide a reliable and easily measured method of assessing intakes. In a predominantly Māori population we compared various sugars intake estimates derived from a 36 item sugar-specific food frequency questionnaire (FFQ) with biomarkers of sugars intake; urinary sugars excretion in random spot collections (n = 153) and carbon stable isotope ratios (n = 36) in red blood cells (RBCs, δ¹³C_RBC) and in the alanine fraction of the RBCs (δ¹³C_alanine). Estimated 24 h urinary sucrose+fructose excretion was statistically significantly correlated with intakes of total sugars (r = 0.23), sucrose (r = 0.26) and added sugars from sugar-sweetened beverages (SSBs; r = 0.26). δ¹³C_alanine was correlated with added sugars (r = 0.40). In log linear multiple regression models adjusted with HbA1C and eGFR δ¹³C_alanine predicted added sugars intakes (r ² = 0.29) and estimated 24 h urinary sucrose+fructose excretion predicted intakes of total sugars (r ² = 0.14), sucrose (r ² = 0.17), added sugars (r ² = 0.17) and sugars from SSBs (r ² = 0.14). These biomarkers have potential for improving assessment of sugars intake in New Zealand populations enabling monitoring of the effectiveness of sugar reduction strategies designed to reduce risk of NCDs. However, further validation is required to confirm these preliminary findings.

Plasma amino acid pools in the umbilical cord artery show lower 15N natural isotope abundance relative to the maternal venous pools

¹⁵N natural isotope abundance (NIA) is systematically higher in infants' hair than in that of their mothers at birth. This study aimed to investigate this difference in plasma pools. We compared ¹⁵N NIA values for plasma amino acid (AA) pools (free + protein-bound) in the umbilical cord artery (UCA) and vein (UCV) and in the maternal vein (MV) at birth. This preliminary study included 7 mother-infant dyads. Whole plasma was treated (HCl) to hydrolyze protein. Following derivatization, AAs were separated using gas chromatography and compound-specific ¹⁵N NIA values were measured on-line using an isotope ratio monitoring mass spectrometer. ¹⁵N NIA plasma AA pools in the UCA and UCV were highly correlated to the MV, r ² > 0.89 and r ² > 0.88 (both P < 10^-4) respectively. The full model found a significant effect of sampling compartment (P = 0.02) and AA type (P < 0.0001) on ¹⁵N NIA plasma AA values. ¹⁵N NIA plasma AA was 0.74 ‰ higher (P = 0.01) in the MV than in the UCA. This study indicates that a decrease in ¹⁵N NIA for plasma AA pools occurs in the fetal-placental unit. Trial registration: ClinicalTrials.gov identifier: NCT00607061.

The carbon isotope ratios of nonessential amino acids identify sugar-sweetened beverage (SSB) consumers in a 12-wk inpatient feeding study of 32 men with varying SSB and meat exposures

BACKGROUND

The carbon isotope ratios (CIRs) of individual amino acids (AAs) may provide more sensitive and specific biomarkers of sugar-sweetened beverages (SSBs) than total tissue CIR. Because CIRs turn over slowly, long-term controlled-feeding studies are needed in their evaluation.

OBJECTIVE

We assessed the responses of plasma and RBC CIRAA's to SSB and meat intake in a 12-wk inpatient feeding study.

METHODS

Thirty-two men (aged 46.2 ± 10.5 y) completed the feeding study at the National Institute of Diabetes and Digestive and Kidney Diseases in Phoenix, Arizona. The effects of SSB, meat, and fish intake on plasma and RBC CIRAA's were evaluated in a balanced factorial design with each dietary variable either present or absent in a common weight-maintaining, macronutrient-balanced diet. Fasting blood samples were collected biweekly from baseline. Dietary effects on the postfeeding CIR of 5 nonessential AAs (CIRNEAA's) and 4 essential AAs (CIREAA's) were analyzed using multivariable regression.

RESULTS

In plasma, 4 of 5 CIRNEAA's increased with SSB intake. Of these, the CIRAla was the most sensitive (β = 2.81, SE = 0.38) to SSB intake and was not affected by meat or fish intake. In RBCs, all 5 CIRNEAA's increased with SSBs but had smaller effect sizes than in plasma. All plasma CIREAA's increased with meat intake (but not SSB or fish intake), and the CIRLeu was the most sensitive (β = 1.26, SE = 0.23). CIRs of leucine and valine also increased with meat intake in RBCs. Estimates of turnover suggest that CIRAA's in plasma, but not RBCs, were in equilibrium with the diets by the end of the study.

CONCLUSIONS

The results of this study in men support CIRNEAA's as potential biomarkers of SSB intake and suggest CIREAA's as potential biomarkers of meat intake in US diets. This trial was registered at clinicaltrials.gov/ct2/show/NCT01237093 as NCT01237093.

The Breath Carbon Isotope Ratio Reflects Short-term Added-Sugar Intake in a Dose-Response, Crossover Feeding Study of 12 Healthy Adults

BACKGROUND

Objective dietary biomarkers are urgently needed for a wider range of foods and nutrients. The breath carbon isotope ratio (CIR; measured as δ13C values) has potential as a noninvasive measure of short-term added sugar (AS) intake but has not been evaluated in a controlled-feeding study.

OBJECTIVE

The aim was to evaluate the effect of short-term AS intake on breath CIR in a dose-response, randomized, crossover feeding study.

METHODS

Six men and 6 women, aged 25 to 60 y, were randomly assigned to a balanced sequence of 5 dietary treatments. Three treatments delivered low (0 g/d), medium (75 g/d), or high (150 g/d) amounts of AS over the course of a single day's breakfast and lunch and 2 switched high and low intake amounts between breakfast and lunch. Experimental meals delivered 60% of daily energy and added-sugar targets. There was a washout period of 1-2 wk between treatments. Breath was collected at 2-h intervals from 08:00 (fasting) to 16:00 h. Breath CIR was measured using cavity ring-down spectroscopy, and the effects of dietary treatments and baseline were evaluated using multivariate linear regression.

RESULTS

Breath CIR showed a significant response to increasing AS intake at all sampling time points (all P < 0.0001), with a dose-response of 0.030 (95% CI: 0.024, 0.037) ‰/g. Fasting breath CIR (baseline) influenced postfeeding breath CIR at all sampling time points (P < 0.0001); however, effect sizes were largest in the morning. For afternoon-collected samples (14:00 and 16:00), the effect of recent AS intake (lunch) was 4-fold greater than the effect of previous added-sugar intake (breakfast).

CONCLUSIONS

These findings support the potential of the breath CIR as a biomarker of short-term AS intake in healthy US adults. More work is needed to evaluate other potential dietary effects and whether multiple breath collections could capture daily AS intake.

Natural abundance carbon isotope ratio analysis and its application in the study of diet and metabolism

Due to differences in carbon assimilation pathways between plants, there are subtle but distinct variations in the carbon isotope ratios of foods and animal products throughout the food supply. Although it is well understood that the carbon isotope ratio composition of the diet influences that of the consumers' tissues, the application of natural abundance carbon isotope ratio analysis in nutrition has long been underappreciated. Over the past decade, however, several studies have investigated the utility of carbon isotope ratio analysis for evaluation of nutritional biomarker status, primarily focusing on its application as an objective indicator of sugar and animal protein intake. More recently, research investigating the application of natural abundance measurements has been extended to study fatty acid metabolism and has yielded encouraging results. Collectively, data from large-scale observational studies and experimental animal studies highlight the potential for carbon isotope ratio analysis as an additional and effective tool to study diet and metabolism. The purpose of this review is to provide an overview of natural abundance carbon isotope ratio analysis, its application to studying nutrition, and an update of the research in the field.

Effect of Organic Food Intake on Nitrogen Stable Isotopes

Food choices affect the isotopic composition of the body with each food item leaving its distinct isotopic imprint. The common view is that the natural abundance of the stable isotopes of nitrogen (expressed as δ¹⁵N) is higher in animals than in plants that constitute our contemporary diets. Higher δ¹⁵N is thus increasingly viewed as a biomarker for meat and fish intake. Here we show that organic compared to conventional farming increases plant δ¹⁵N to an extent that can appreciably impact the performance of δ¹⁵N as a biomarker. The error that can arise when organic plants are consumed was modelled for the entire range of proportions of plant versus animal protein intake, and accounting for various intakes of organic and conventionally grown crops. This mass balance model allows the interpretation of differences in δ¹⁵N in light of organic food consumption. Our approach shows that the relationship between δ¹⁵N and meat and fish intake is highly contextual and susceptible to variation at the population, community or group level. We recommend that fertilization practices and organic plant consumption must not be overlooked when using δ¹⁵N as a biomarker for meat and fish intake or to assess compliance to nutritional interventions.

Stable isotopes in hair reveal dietary protein sources with links to socioeconomic status and health

Carbon and nitrogen isotope ratios in hair sampled from 65 communities across the central and intermountain regions of the United States and more intensively throughout 29 ZIP codes in the Salt Lake Valley, Utah, revealed a dietary divergence related to socioeconomic status as measured by cost of living, household income, and adjusted gross income. Corn-fed, animal-derived proteins were more common in the diets of lower socioeconomic status populations than were plant-derived proteins, with individual estimates of animal-derived protein diets as high as 75%; United States towns and cities averaged 57%. Similar patterns were seen across the socioeconomic status spectrum in the Salt Lake Valley. It is likely that corn-fed animal proteins were associated with concentrated animal-feeding operations, a common practice for industrial animal production in the United States today. Given recent studies highlighting the negative impacts of animal-derived proteins in our diets, hair carbon isotope ratios could provide an approach for scaling assessments of animal-sourced foods and health risks in communities across the United States.

How isotopic signatures relate to meat consumption in wild chimpanzees: A critical reference study from Taï National Park, Côte d'Ivoire

The roots of human hunting and meat eating lie deep in our evolutionary past shared with chimpanzees (Pan troglodytes). From the few habituated wild populations, we know that there is considerable variation in the extent to which chimpanzees consume meat. Expanding our knowledge of meat eating frequencies to more, yet unhabituated, populations requires noninvasive, indirect quantitative techniques. We here evaluate the use of stable isotopes to reconstruct meat-eating behavior in wild chimpanzees. We present hair isotope data (n = 260) of two western chimpanzee (P. troglodytes verus) groups from Taï forest (Côte d'Ivoire) and relate them to directly observed amounts of meat consumed, sex/female reproductive state, and group, while controlling for differences between individuals, seasons, and observation efforts. Succeeding seven months of hunting observations, we collected hair of 25 individuals for sequential analysis of δ¹⁵N and δ¹³C. Hunting success in the 7-month study period varied between the groups, with 25 successful hunts in the East group and only 8 in the North group. However, our models only found a direct relationship between amounts of meat consumed and variation within individual hair δ¹⁵N values in the East group, but not in the North group and not when comparing between individuals or groups. Although on average East group individuals consumed more than double the amount of meat than North group individuals, their δ¹⁵N values were significantly lower, suggesting that differences in microhabitat are substantial between group territories. The effect of sex/female reproductive state was significant in δ¹⁵N and δ¹³C, suggesting it related to access to food or feeding preferences. We conclude that several factors additional to diet are influencing and thus obscuring the isotope ratios in wild chimpanzee hair, particularly when comparing between sexes and social groups.

Amazake made from sake cake and rice koji suppresses sebum content in differentiated hamster sebocytes and improves skin properties in humans

Amazake is a traditional Japanese health drink. Here, we examined the effects of amazake on skin in cells and humans. Treatment with sake cake or rice koji suppressed intracellular lipid accumulation in differentiated hamster sebocytes, likely through the reduced expression of peroxisome proliferator-activated receptor-gamma (PPARγ) mRNA. In double-blind, placebo-controlled trial, seventeen Japanese women ingested either amazake or placebo for 4 weeks. Ingestion of the amazake decreased the sebum content compared to the placebo. The questionnaires showed improvements in "face color," "dark circles under the eyes," "glossy hair," and "waking up well", only in the amazake. In accordance with the questionnaires, additional analysis revealed the change in the L* values under the eyes was statistically increased in the amazake compared to the placebo. These results indicate that amazake may decrease sebum content in cells and humans and increase the L* values under the eyes, with some additional beneficial effects in humans.

Weaning and stunting affect nitrogen and carbon stable isotope natural abundances in the hair of young children

Natural abundances of stable nitrogen and carbon isotopes (δ¹⁵N and δ¹³C) can vary with both dietary intake and metabolic (specifically catabolic) state. In low-income countries, weaning is a period of dietary transition from milk to plant-based foods and a high-risk period for malnutrition. We explored how diet and malnutrition impact hair δ¹⁵N and δ¹³C in young children by an observational, cross-sectional study in Cox’s Bazar District, Bangladesh [255 children, 6–59 months with 19.6% wasted (7.1% severely) and 36% stunted (9.8% severely)]. Hair δ¹⁵N and δ¹³C exhibited exponential decreases with age, with the loss of one trophic level (3.3‰ and 0.8‰, respectively) from 6 to 48 months, which we associate with the shift from exclusive breastfeeding to complete weaning. After adjustment for age and breastfeeding status, hair isotopic values were unaffected by wasting but lower in severe stunting (−0.45‰ to −0.6‰, P < 0.01). In this population of young children, whose isotopic values in hair primarily depended on age, we failed to observe any effect of wasting, likely due to opposite, compensating effects between dietary and metabolic changes involved. In contrast, we evidenced low δ¹⁵N and δ¹³C values in severely stunted children that likely indicate chronic exposure to diets low in animal products.

Biomarkers of meat and seafood intake: an extensive literature review

Meat, including fish and shellfish, represents a valuable constituent of most balanced diets. Consumption of different types of meat and fish has been associated with both beneficial and adverse health effects. While white meats and fish are generally associated with positive health outcomes, red and especially processed meats have been associated with colorectal cancer and other diseases. The contribution of these foods to the development or prevention of chronic diseases is still not fully elucidated. One of the main problems is the difficulty in properly evaluating meat intake, as the existing self-reporting tools for dietary assessment may be imprecise and therefore affected by systematic and random errors. Dietary biomarkers measured in biological fluids have been proposed as possible objective measurements of the actual intake of specific foods and as a support for classical assessment methods. Good biomarkers for meat intake should reflect total dietary intake of meat, independent of source or processing and should be able to differentiate meat consumption from that of other protein-rich foods; alternatively, meat intake biomarkers should be specific to each of the different meat sources (e.g., red vs. white; fish, bird, or mammal) and/or cooking methods. In this paper, we present a systematic investigation of the scientific literature while providing a comprehensive overview of the possible biomarker(s) for the intake of different types of meat, including fish and shellfish, and processed and heated meats according to published guidelines for biomarker reviews (BFIrev). The most promising biomarkers are further validated for their usefulness for dietary assessment by published validation criteria.

Associations of plasma, RBCs, and hair carbon and nitrogen isotope ratios with fish, meat, and sugar-sweetened beverage intake in a 12-wk inpatient feeding study

BACKGROUND

Naturally occurring carbon and nitrogen stable isotope ratios [13C/12C (CIR) and 15N/14N (NIR)] are promising dietary biomarkers. As these candidate biomarkers have long tissue residence times, long-term feeding studies are needed for their evaluation.

OBJECTIVE

Our aim was to evaluate plasma, RBCs, and hair CIR and NIR as biomarkers of fish, meat, and sugar-sweetened beverage (SSB) intake in a 12-wk dietary intervention.

METHODS

Thirty-two men (aged 46.2 ± 10.5 y; BMI: 27.2 ± 4.0 kg/m2) underwent a 12-wk inpatient dietary intervention at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) in Phoenix, Arizona. The effects of fish, meat, and SSB intake on CIR and NIR were evaluated using a balanced factorial design, with each intake factor at 2 levels (present/absent) in a common, background diet (50% carbohydrate, 30% fat, 20% protein). Fasting blood samples were taken biweekly from baseline, and hair samples were collected at baseline and postintervention. Data were analyzed using multivariable regression.

RESULTS

The postintervention CIR of plasma was elevated when diets included meat (β = 0.89, 95% CI: 0.73,1.05) and SSBs (β = 0.48, 95% CI: 0.32, 0.64). The postintervention NIR of plasma was elevated when diets included fish (β = 0.85, 95% CI: 0.64, 1.05) and meat (β = 0.61, 95% CI: 0.42, 0.8). Results were similar for RBCs and hair. Postintervention RBC CIR and NIR had strong associations with baseline, suggesting that turnover to the intervention diets was incomplete after 12 wk. Estimates of isotopic turnover rate further confirmed incomplete turnover of RBCs.

CONCLUSIONS

CIR was associated with meat and SSBs, and more strongly with meat. NIR was associated with fish and meat, and more strongly with fish. Overall, CIR and NIR discriminated between dietary fish and meat, and to a lesser extent SSBs, indicating their potential utility as biomarkers of intake in US diets. Approaches to make these biomarkers more specific are needed. This trial was registered at clinicaltrials.gov as NCT01237093.

Maternal obesity does not influence human milk protein 15N natural isotope abundance

Obesity increases protein metabolism with a potential effect on nitrogen isotope fractionation. The aim of this study was to test the influence of obesity on human milk extracted protein ¹⁵N natural isotope abundance (NIA) at one month post-partum and to compare human milk extracted protein ¹⁵N NIA and bulk infant hair ¹⁵N NIA. This cross-sectional observational study involved 16 obese mothers (body mass index (BMI) ≥ 30 kg m^-2 before pregnancy) matched with 16 normal-weight mothers (18.5 kg m^-2 ≤ BMI < 25 kg m^-2) for age and pregnancy characteristics. Human milk extracted protein and bulk infant hair ¹⁵N NIA were determined by isotope ratio monitoring by mass spectrometry interfaced to an elemental analyser (IRM-EA/MS). No significant difference was found in human milk protein ¹⁵N NIA values between obese and normal-weight mothers (8.93 ± 0.48 ‰ vs. 8.95 ± 0.27 ‰). However, human milk protein ¹⁵N NIA was significantly lower than bulk infant hair ¹⁵N NIA: 8.94 ± 0.38 ‰ vs. 9.66 ± 0.69 ‰, respectively. On the basis of these results, it is concluded that human milk protein ¹⁵N NIA measured at one month post-partum is not influenced by maternal obesity. These findings suggest that ¹⁵N NIA may be exploited to study metabolism without considering maternal obesity as a confounder.

The Skiles Mummy: Care of a debilitated hunter-gatherer evidenced by coprolite studies and stable isotopic analysis of hair

The Skiles Mummy (SMM), a naturally mummified adult male from the late archaic period of Lower Pecos Canyonlands of South Texas, represents a unique case of care. SMM is an exceptional mummy within this region due to both the retention of a full head of hair, and having a diagnosed case of megacolon, a complication commonly associated with Chagas disease caused by Trypanosoma cruzi. Stable isotopic analysis of his hair is consistent with a diet incorporating of C₄/CAM plants with some C₃ plants, freshwater resources, and higher trophic level animals. However, the segments of hair most proximal to the scalp exhibited elevated δ¹⁵N values. Data from previous research indicate starvation and malnutrition can cause δ¹⁵N values to rise. The presence of large fecal boluses in the digestive tract suggest peristalsis ceased in the last four to five months of life, and this, together with results from coprolite analysis, indicate he would not have been able to adequately absorb protein and nutrients during this time. His condition would have rendered him immobile. Following Tilley's index of care, someone would have had to bring him food resources, as well as attending to his daily needs.

Serum Nitrogen and Carbon Stable Isotope Ratios Meet Biomarker Criteria for Fish and Animal Protein Intake in a Controlled Feeding Study of a Women's Health Initiative Cohort

Background

Natural abundance stable isotope ratios are candidate biomarkers of dietary intake that have not been evaluated in a controlled feeding study in a US population.

Objectives

Our goals were to evaluate dietary associations with serum carbon (CIR), nitrogen (NIR), and sulfur (SIR) isotope ratios in postmenopausal women, and to evaluate whether statistical models of dietary intake that include multiple isotopes and participant characteristics meet criteria for biomarker evaluation.

Methods

Postmenopausal women from the Women's Health Initiative (n = 153) were provided a 2-wk controlled diet that approximated each individual's habitual food intake. Dietary intakes of animal protein, fish/seafood, red meat, poultry, egg, dairy, total sugars, added sugars, sugar-sweetened beverages (SSBs), and corn products were characterized during the feeding period with the use of the Nutrition Data System for Research (NDS-R). The CIR, NIR, and SIR were measured in sera collected from fasting women at the beginning and the end of the feeding period. Linear models based on stable isotope ratios and participant characteristics predicted dietary intake. The criterion used for biomarker evaluation was R2 ≥ 0.36, based on the study's power to detect true associations with R2 ≥ 0.50.

Results

The NIR was associated with fish/seafood intake and met the criterion for biomarker evaluation (R2 = 0.40). The CIR was moderately associated with intakes of red meat and eggs, but not to the criterion for biomarker evaluation, and was not associated with intake of sugars (total, added, or SSB). A model of animal protein intake based on the NIR, CIR, and participant characteristics met the criterion for biomarker evaluation (R2 = 0.40). Otherwise, multiple isotopes did not improve models of intake, and improvements from including participant characteristics were modest.

Conclusion

Serum stable isotope ratios can, with participant characteristics, meet biomarker criteria as measures of fish/seafood and animal protein intake in a sample of postmenopausal women. This trial was registered at clinicaltrials.gov as NCT00000611.

Protein restricted diet during gestation and/or lactation in mice affects 15N natural isotopic abundance of organs in the offspring: Effect of diet 15N content and growth

OBJECTIVES AND STUDY

This study aimed at measuring the effect in normal to restricted protein diets with specific 15N natural isotopic abundance (NIA) given during gestation and/or lactation on the 15N NIA of fur, liver and muscle in dams and their offspring from birth to adulthood. The secondary aim was to study the effect of growth on the same parameters.

METHODS

Female Balb/c mice were fed normal protein diet containing 22% protein or isocaloric low protein diet containing 10% protein throughout gestation. Dam's diets were either maintained or switched to the other diet until weaning at 30 days. All animals were fed standard chow thereafter. Offspring were sacrificed at 1, 11, 30, 60, 480 days and a group of dams at d1. Growth was modeled as an exponential function on the group followed up until 480 days. Fur, liver and muscle were sampled at sacrifice and analyzed for bulk 15N NIA. Fixed effects and interactions between fixed effects and random elements were tested by three-way ANOVA.

RESULTS

Higher 15N NIA in the diet resulted in higher organ 15N NIA. Switching from one diet to another changed 15N NIA in each organ. Although dam and offspring shared the same isotopic environment during gestation, 15N NIA at day 1 was higher in dams. Growth rate did not differ between groups after 10 days and decreased between 1 and 5 months. 15N NIA differed between organs and was affected by growth and gestation/lactation.

CONCLUSION

Dietary 15N NIA is a major determinant of the 15N NIA of organs. 15N NIA depended on organ and age (i.e. growth) suggesting an effect of metabolism and/or dilution space. Post-natal normal-protein diet of lactating dams could reverse the effect of a protein-restricted diet during gestation on the offspring growth. Measuring 15N NIA in various matrices may open a field of application particularly useful in studying the pre- and post-natal origins of health and disease.

Parasites in Myodes glareolus and their association with diet assessed by stable isotope analysis

Vertebrates are hosts to numerous parasites, belonging to many different taxa. These parasites differ in transmission, being through either direct contact, a faecal-oral route, ingestion of particular food items, vertical or sexual transmission, or by a vector. Assessing the impact of diet on parasitism can be difficult because analysis of faecal and stomach content are uncertain and labourious; and as with molecular methods, do not provide diet information over a longer period of time. We here explored whether the analysis of stable isotopes in hair provides insight into the impact of diet and the presence of parasites in the rodent Myodes glareolus. Twenty-one animals were examined for parasites and their hair analysed for stable isotopes (C and N). A positive correlation between δ15N and one species of intestinal parasite was observed in females. Furthermore, several ectoparasites were negatively correlated with δ15N, indicating that infections are further associated with foraging habits (size and layout of the home range, length and timing of foraging, interaction with other rodents, etc.) that set the rodents in direct contact with infected hosts. Although a limited number of animals were included, it seemed that the isotope values allowed for identification of the association between diet and parasite occurrence in this rodent. We therefore propose that this method is useful in providing further insight into host biology, feeding preferences and potential exposure to parasites species, contributing to the understanding of the complex relationship between hosts and parasites.

Association between Nitrogen Stable Isotope Ratios in Human Hair and Serum Levels of Leptin

Stable isotope ratios have been reported to be potential biomarkers of dietary intake and nutritional status. High serum levels of leptin, a hormone which regulates energy metabolism and food intake, are associated with insulin resistance and metabolic syndrome. However, little is known about the association between stable isotope ratios and the metabolic risk in humans. We investigated whether the carbon and nitrogen stable isotope ratios in hair are associated with serum leptin levels. Hair samples were collected from 399 healthy adults (233 men and 166 women) aged 40 to 70 years of a community-based cohort in Korea and the bulk stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were measured for all hair samples. Serum leptin levels were analyzed by radioimmunoassay. δ¹⁵N showed positive correlations with serum leptin levels. In multivariate models, increasing δ¹⁵N were associated with elevated serum leptin levels (defined as ≥ the median values), whereas δ¹³C were not significantly associated with serum leptin levels. The odds ratio (95% confidence interval) per 1‰ increase in δ¹⁵N for an elevated serum leptin level was 1.58 (1.11-2.26). In participants with high body mass index, δ¹⁵N showed positive associations with serum leptin levels, whereas these associations were not seen in participants with low body mass index. The nitrogen stable isotopic ratio in hair is positively associated with serum leptin levels. The hair δ¹⁵N could be used as a clinical marker to estimate metabolic risk.

Evaluation of childhood nutrition by dietary survey and stable isotope analyses of hair and breath

OBJECTIVES

The natural abundances of carbon, nitrogen, and sulfur stable isotopes in hair, and of carbon isotopes in breath serve as quantitative biomarkers of protein and carbohydrate sources, but applicability of isotopes for evaluating children's diet has not been demonstrated. In this study, we sought to describe the stable isotope patterns observed in the hair and breath of children and to assess dietary variations in relation to age and ethnicity, hypothesizing that these would reflect dietary differences across age and ethnic groups and would correlate with intake variables derived from a Food Frequency Questionnaire.

METHODS

Data were obtained from a cross-sectional study of non-Hispanic white (N = 115) and Hispanic (N = 97) children, aged 9-16 years, in Salt Lake City, Utah. Sampling included a hair sample, breath samples (AM and PM), and a youth/adolescent food questionnaire (YAQ). Hair was analyzed for carbon (δ¹³ C), nitrogen (δ¹⁵ N), and sulfur (δ³⁴ S) isotopes, and breath samples for δ¹³ C_AM/PM of respired CO₂ .

RESULTS

Non-Hispanic whites had lower δ¹³ C, δ¹⁵ N, δ¹³ C_AM , and δ¹³ C_PM values than Hispanics. Hair δ¹³ C and δ¹⁵ N values were correlated with protein sources, particularly for non-Hispanics. Breath δ¹³ C values were correlated with carbohydrate sources, particularly for Hispanic students. Non-Hispanic white students reported greater intake of total protein, animal protein, dairy, and grain than Hispanic students. Hispanic students reported higher intake of carbohydrates, particularly sweetened beverages.

CONCLUSION

While YAQ and stable isotope data reflected strong cultural influences in diet, no significant gender-based nor age-based differences were detected. Significant covariation between YAQ and isotopes existed and demonstrate the potential of stable isotopes for characterizing children's diet.

Isotope (δ13C, δ15N, δ2H) diet-tissue discrimination in African grey parrot Psittacus erithacus: implications for forensic studies

Diet-tissue isotopic relationships established under controlled conditions are informative for determining the dietary sources and geographic provenance of organisms. We analysed δ¹³C, δ¹⁵N, and non-exchangeable δ²H values of captive African grey parrot Psittacus erithacus feathers grown on a fixed mixed-diet and borehole water. Diet-feather Δ¹³C and Δ¹⁵N discrimination values were +3.8 ± 0.3 ‰ and +6.3 ± 0.7 ‰ respectively; significantly greater than expected. Non-exchangeable δ²H feather values (-62.4 ± 6.4 ‰) were more negative than water (-26.1 ± 2.5 ‰) offered during feather growth. There was no positive relationship between the δ¹³C and δ¹⁵N values of the samples along each feather with the associated samples of food offered, or the feather non-exchangeable hydrogen isotope values with δ²H values of water, emphasising the complex processes involved in carbohydrate, protein, and income water routing to feather growth. Understanding the isotopic relationship between diet and feathers may provide greater clarity in the use of stable isotopes in feathers as a tool in determining origins of captive and wild-caught African grey parrots, a species that is widespread in aviculture and faces significant threats to wild populations. We suggest that these isotopic results, determined even in controlled laboratory conditions, be used with caution.

Isotopic assessment of marine food consumption by natural-foraging chacma baboons on the Cape Peninsula, South Africa

OBJECTIVES

Stable isotope analysis has been used to investigate consumption of marine resources in a variety of terrestrial mammals, including humans, but not yet in extant nonhuman primates. We sought to test the efficacy of stable isotope analysis as a tool for such studies by comparing isotope- and observation-based estimates of marine food consumption by a troop of noncommensal, free-ranging chacma baboons.

MATERIALS AND METHODS

We determined δ¹³ C and δ¹⁵ N values of baboon hair (n = 9) and fecal samples (n = 144), and principal food items (n = 362). These values were used as input for diet models, the outputs of which were compared to observation-based estimates of marine food consumption.

RESULTS

Fecal δ¹³ C values ranged from -29.3‰ to -25.6‰. δ¹⁵ N values ranged from 0.9‰ to 6.3‰ and were positively correlated with a measure of marine foraging during the dietary integration period. Mean (± SD) δ¹³ C values of adult male and female baboon hairs were -21.6‰ (± 0.1) and -21.8‰ (± 0.3) respectively, and corresponding δ¹⁵ N values were 5.0‰ (± 0.3) and 3.9‰ (± 0.2). Models indicated that marine contributions were ≤10% of baboon diet within any season, and contributed ≤17% of dietary protein through the year.

DISCUSSION

Model output and observational data were in agreement, both indicating that despite their abundance in the intertidal region, marine foods comprised only a small proportion of baboon diet. This suggests that stable isotope analysis is a viable tool for investigating marine food consumption by natural-foraging primates in temperate regions.

Natural Isotope Abundance in Metabolites: Techniques and Kinetic Isotope Effect Measurement in Plant, Animal, and Human Tissues

The natural isotope abundance in bulk organic matter or tissues is not a sufficient base to investigate physiological properties, biosynthetic mechanisms, and nutrition sources of biological systems. In fact, isotope effects in metabolism lead to a heterogeneous distribution of ²H, ¹⁸O, ¹³C, and ¹⁵N isotopes in metabolites. Therefore, compound-specific isotopic analysis (CSIA) is crucial to biological and medical applications of stable isotopes. Here, we review methods to implement CSIA for ¹⁵N and ¹³C from plant, animal, and human samples and discuss technical solutions that have been used for the conversion to CO₂ and N₂ for IRMS analysis, derivatization and isotope effect measurements. It appears that despite the flexibility of instruments used for CSIA, there is no universal method simply because the chemical nature of metabolites of interest varies considerably. Also, CSIA methods are often limited by isotope effects in sample preparation or the addition of atoms from the derivatizing reagents, and this implies that corrections must be made to calculate a proper δ-value. Therefore, CSIA has an enormous potential for biomedical applications, but its utilization requires precautions for its successful application.

Prediction of human dietary δ15N intake from standardised food records: validity and precision of single meal and 24-h diet data

Natural stable isotope ratios (δ¹⁵N) of humans can be used for nutritional analyses and dietary reconstruction of modern and historic individuals and populations. Information about an individual's metabolic state can be obtained by comparison of tissue and dietary δ¹⁵N. Different methods have been used to estimate dietary δ¹⁵N in the past; however, the validity of such predictions has not been compared to experimental values. For a total of 56 meals and 21 samples of 24-h diets, predicted and experimental δ¹⁵N values were compared. The δ¹⁵N values were predicted from self-recorded food intake and compared with experimental δ¹⁵N values. Predicted and experimental δ¹⁵N values were in good agreement for meals and preparations (r = 0.89, p < .001) as well as for the 24-h diets (r = 0.76, p < .001). Dietary δ¹⁵N was mainly determined by the amount of fish, whereas the contribution of meat to dietary δ¹⁵N values was less pronounced. Prediction of human dietary δ¹⁵N values using standardised food records and representative δ¹⁵N data sets yields reliable data for dietary δ¹⁵N intake. A differentiated analysis of the primary protein sources is necessary when relating the proportion of animal-derived protein in the diet by δ¹⁵N analysis.

'Trophic' and 'source' amino acids in trophic estimation: a likely metabolic explanation

Amino acid nitrogen isotopic analysis is a relatively new method for estimating trophic position. It uses the isotopic difference between an individual's 'trophic' and 'source' amino acids to determine its trophic position. So far, there is no accepted explanation for the mechanism by which the isotopic signals in 'trophic' and 'source' amino acids arise. Yet without a metabolic understanding, the utility of nitrogen isotopic analyses as a method for probing trophic relations, at either bulk tissue or amino acid level, is limited. I draw on isotopic tracer studies of protein metabolism, together with a consideration of amino acid metabolic pathways, to suggest that the 'trophic'/'source' groupings have a fundamental metabolic origin, to do with the cycling of amino-nitrogen between amino acids. 'Trophic' amino acids are those whose amino-nitrogens are interchangeable, part of a metabolic amino-nitrogen pool, and 'source' amino acids are those whose amino-nitrogens are not interchangeable with the metabolic pool. Nitrogen isotopic values of 'trophic' amino acids will reflect an averaged isotopic signal of all such dietary amino acids, offset by the integrated effect of isotopic fractionation from nitrogen cycling, and modulated by metabolic and physiological effects. Isotopic values of 'source' amino acids will be more closely linked to those of equivalent dietary amino acids, but also modulated by metabolism and physiology. The complexity of nitrogen cycling suggests that a single identifiable value for 'trophic discrimination factors' is unlikely to exist. Greater consideration of physiology and metabolism should help in better understanding observed patterns in nitrogen isotopic values.

The dietary protein paradox and threonine 15 N-depletion: Pyridoxal-5'-phosphate enzyme activity as a mechanism for the δ15 N trophic level effect

RATIONALE

Nitrogen stable isotope ratios (δ¹⁵ N values) are used to reconstruct dietary patterns, but the biochemical mechanism(s) responsible for the diet to tissue trophic level effect and its variability are not fully understood. Here δ¹⁵ N amino acid (AA) values and physiological measurements (nitrogen intake, plasma albumin concentrations, liver-reduced glutathione concentrations and leucine oxidation rates) are used to investigate increased dietary protein consumption and oxidative stress (vitamin E deficiency) in rat total plasma protein.

METHODS

Using gas chromatography/combustion/isotope ratio mass spectrometry, the δ¹⁵ N values from N-pivaloyl-i-propyl esters of 15 AAs are reported for rats (n = 40) fed casein-based diets with: adequate protein (AP, 13.8%; n = 10), medium protein (MP, 25.7%; n = 10), high protein (HP, 51.3%; n = 10) or HP without vitamin E (HP-E; n = 10) for 18 weeks.

RESULTS

Between the HP and AP groups, the δ¹⁵ N_AA values of threonine (-4.0‰), serine (+1.4‰) and glycine (+1.2‰) display the largest differences and show significant correlations with: nitrogen intake, plasma albumin concentrations, liver-reduced glutathione concentrations and leucine oxidation rates. This indicates increased AA catabolism by the dietary induction of shared common metabolic pathways involving the enzymes threonine ammonia-lyase (EC 4.3.1.19), serine hydroxymethyltransferase (EC 2.1.2.1) and the glycine cleavage system (EC 2.1.2.10). The δ¹⁵ N_AA values of the HP-E and HP groups were not found to be significantly different.

CONCLUSIONS

The ¹⁵ N-depleted results of threonine are linked to increased activity of threonine ammonia-lyase, and show potential as a possible biomarker for protein intake and/or gluconeogenesis. We hypothesize that the inverse nitrogen equilibrium isotope effects of Schiff base formation, between AAs and pyridoxal-5'-phosphate cofactor enzymes, play a key role in the bioaccumulation and depletion of ¹⁵ N in the biomolecules of living organisms and contributes to the variability in the nitrogen trophic level effect. Copyright © 2017 John Wiley & Sons, Ltd.

Case of Fatal Starvation: Can Stable Isotope Analysis Serve to Support Morphological Diagnosis and Approximate the Length of Starvation?

The diagnosis of death as a result of starvation is established on anthropological measurements, visual appearance of the deceased on external and internal examination, microscopic analysis, laboratory testing, and exclusion of other causes of death. Herein, we present our findings on a case of 95-year-old man who died of starvation. After the diagnosis of starvation was established by traditional forensic medicine methods, we have conducted retrospective segmental analysis of stable carbon (δ¹³ C) and nitrogen (δ¹⁵ N) isotope ratios in hair sample. This method reveals periods of starvation through decrease in δ¹³ C and increase in δ¹⁵ N along the strand of hair. Our analysis revealed the decrease of 0.6 ‰ in δ¹³ C during the last 10-12 weeks prior to death, similar as reported in other investigations. Also, a decrease of 0.7 ‰ in δ¹⁵ N during the last 8-10 weeks prior to death was determined that was different than observed in previous studies.

Nitrogen isotopic discrimination in dietary amino acids: The threonine anomaly

RATIONALE

The "Threonine Anomaly" relates to an observation made 25 years ago on the change in Thr nitrogen isotopic ratio in mammalian metabolism. Unlike all other amino acids, Thr in body protein is found to be depleted (rather than enriched) in ¹⁵ N relative to dietary Thr. Interpreting isotopic discrimination has become a useful source of ecological and palaeodietary information and it is desirable that the underlying processes are understood.

METHODS

The principal enzyme of threonine catabolism, suggested to be responsible for the anomaly, threonine dehydratase, was prepared from rat liver. A time course of incubation of the enzyme with pure threonine was followed, and samples of residual threonine prepared for isotopic analysis by combustion in an automated carbon and nitrogen analyser coupled to a continuous flow isotope ratio mass spectrometer.

RESULTS

We show experimentally, in vitro, that the enzymic reaction catabolising Thr cannot be responsible for its ¹⁵ N depletion. Plots of delta ¹⁵ N against both reaction time course and percentage completion show in fact an accelerating enrichment.

CONCLUSIONS

A previously advanced suggestion that the unique catabolic mechanism for threonine was responsible for the anomalous depletion in ¹⁵ N is clearly not the case. We therefore offer alternative explanations, based on threonine's role at an organismal rather than cellular level. Copyright © 2016 John Wiley & Sons, Ltd.

13C and 15N natural isotope abundance reflects breast cancer cell metabolism

Breast cancer is the most common cancer in women worldwide. Despite the information provided by anatomopathological assessment and molecular markers (such as receptor expression ER, PR, HER2), breast cancer therapies and prognostics depend on the metabolic properties of tumor cells. However, metabolomics have not provided a robust and congruent biomarker yet, likely because individual metabolite contents are insufficient to encapsulate all of the alterations in metabolic fluxes. Here, we took advantage of natural ¹³C and ¹⁵N isotope abundance to show there are isotopic differences between healthy and cancer biopsy tissues or between healthy and malignant cultured cell lines. Isotope mass balance further suggests that these differences are mostly related to lipid metabolism, anaplerosis and urea cycle, three pathways known to be impacted in malignant cells. Our results demonstrate that the isotope signature is a good descriptor of metabolism since it integrates modifications in C partitioning and N excretion altogether. Our present study is thus a starting point to possible clinical applications such as patient screening and biopsy characterization in every cancer that is associated with metabolic changes.

Limits and possibilities in the geolocation of humans using multiple isotope ratios (H, O, N, C) of hair from east coast cities of the USA

We examined multiple natural abundance isotope ratios of human hair to assess biological variability within and between geographic locations and, further, to determine how well these isotope values predict location of origin. Sampling locations feature differing seasonality and mobile populations as a robust test of the method. Serially-sampled hair from Cambridge, MA, USA, shows lower δ(2)H and δ(18)O variability over a one-year time course than model-predicted precipitation isotope ratios, but exhibits considerable differences between individuals. Along a ∼13° north-south transect in the eastern USA (Brookline, MA, 42.3 ° N, College Park, MD, 39.0 ° N, and Gainesville, FL, 29.7 ° N) δ(18)O in human hair shows relatively greater differences and tracks changes in drinking water isotope ratios more sensitively than δ(2)H. Determining the domicile of humans using isotope ratios of hair can be confounded by differing variability in hair δ(18)O and δ(2)H between locations, differential incorporation of H and O into this protein and, in some cases, by tap water δ(18)O and δ(2)H that differ significantly from predicted precipitation values. With these caveats, randomly chosen people in Florida are separated from those in the two more northerly sites on the basis of the natural abundance isotopes of carbon, nitrogen, hydrogen, and oxygen.

Re-constructing nutritional history of Serengeti wildebeest from stable isotopes in tail hair: seasonal starvation patterns in an obligate grazer

RATIONALE

Nutritional bottlenecks often limit the abundance of animal populations and alter individual behaviours; however, establishing animal condition over extended periods of time using non-invasive techniques has been a major limitation in population ecology. We test if the sequential measurement of δ(15) N values in a continually growing tissue, such as hair, can be used as a natural bio-logger akin to tree rings or ice cores to provide insights into nutritional stress.

METHODS

Nitrogen stable isotope ratios were measured by continuous-flow isotope-ratio mass spectrometry (IRMS) from 20 sequential segments along the tail hairs of 15 migratory wildebeest. Generalized Linear Models were used to test for variation between concurrent segments of hair from the same individual, and to compare the δ(15) N values of starved and non-starved animals. Correlations between δ(15) N values in the hair and periods of above-average energy demand during the annual cycle were tested using Generalized Additive Mixed Models.

RESULTS

The time series of nitrogen isotope ratios in the tail hair are comparable between strands from the same individual. The most likely explanation for the pattern of (15) N enrichment between individuals is determined by life phase, and especially the energetic demands associated with reproduction. The mean δ(15) N value of starved animals was greater than that of non-starved animals, suggesting that higher δ(15) N values correlate with periods of nutritional stress.

CONCLUSIONS

High δ(15) N values in the tail hair of wildebeest are correlated with periods of negative energy balance, suggesting they may be used as a reliable indicator of the animal's nutritional history. This technique might be applicable to other obligate grazers. Most importantly, the sequential isotopic analysis of hair offers a continuous record of the chronic condition of wildebeest (effectively converting point data into time series) and allows researchers to establish the animal's nutritional diary.