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

Carbon stable isotope values in hair are associated with added sugar intake in adults but not young children: a cross-sectional study

BACKGROUND

Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios in tissues are proposed biomarkers for dietary intake, with δ13C values reflecting added sugar intake derived from corn and sugarcane, and δ15N values reflecting animal protein intake. Research in young children is limited.

OBJECTIVE

We examined associations between hair δ13C and δ15N values and dietary intake among children and also their mothers, to confirm associations found in other adults.

METHODS

Hair samples and 24-h dietary recalls were collected from children (aged 5.6 ± 0.2 y; n = 138) and adults (34.1 ± 0.7 y; n = 114) in a cross-sectional study in Philadelphia. Hair δ13C and δ15N values were determined by continuous-flow isotope ratio mass spectrometry. Intake assessments focused on foods with high δ13C values [e.g. sugar-sweetened beverages (SSB)], high δ15N values (e.g. meat), or both (e.g. cow's milk). Three analytical approaches-single- (δ13C), dual- (δ13C, δ15N) isotope regression models and, uniquely, k-means cluster analysis-were used to assess associations.

RESULTS

Among adults, regression models revealed positive associations of δ13C values with added sugar [β (95% confidence interval): single, 0.17 (-0.01, 0.36); dual, 0.31 (0.10, 0.53)] and SSB [single, 0.30 (0.12, 0.48); dual, 0.31 (0.09, 0.53)] intakes, confirming prior findings. Adults in the high δ13C-δ15N cluster drank more SSB than the low cluster (213 ± 23 compared with 109 ± 20 kcal/d, P = 0.03). Among children, no such associations were found. However, children in the high δ13C-δ15N cluster consumed more cow's milk (81 ± 9 compared with 31 ± 7 kcal/d, P = 0.009) and animal proteins (408 ± 33 compared with 272 ± 36 kcal/d, P = 0.04). Their cow's milk intake is significantly associated with δ13C and δ15N values.

CONCLUSIONS

Age-related dietary patterns, particularly higher cow's milk consumption in children, may mask δ13C-added sugar associations, highlighting the importance of accounting for age and dietary complexity in biomarker research. This study was registered at: Snacks, Smiles and Taste Preferences as registration number NCT03631992. Website: https://clinicaltrials.gov/study/NCT03631992; Added Sugar Intake, Sweet Taste Phenotypes and Biomarkers (SWBIO), NCT05047588. Website: https://clinicaltrials.gov/ct2/show/NCT05047588.

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.

The carbon isotope ratio of breath is elevated by short-term and long-term added sugar and animal protein intake in a controlled feeding study

BACKGROUND

The breath carbon isotope ratio (CIR) was recently identified as a noninvasive candidate biomarker of short-term added sugars (AS) intake.

OBJECTIVES

This study aimed to better understand the potential of the breath CIR as a dietary biomarker. We evaluated the effects of short-term and long-term intakes of AS, animal protein (AP), and related variables on breath CIR, in the context of typical dietary intake patterns.

METHODS

We conducted a 15-d controlled feeding study of 100 adults (age 18-70 y, 55% females) in Phoenix, AZ. Participants were provided individualized diets that approximated habitual food intakes and recorded the timing of food consumption. Three breath samples (fasting, midday, and evening) were collected on each of 3 nonconsecutive study days. We modeled the effects of dietary intake in each of 8 h preceding collection of the breath sample on breath CIR with a linear mixed model, which also included 15-d mean intakes, sex, age, and BMI.

RESULTS

Median (IQR) intakes of AS and AP in our study were 65 (38) and 67 (33) g/d, respectively. Midday and evening breath CIRs correlated strongly with each other (0.80) and with fasting breath CIR (0.77 and 0.68, respectively). In our linear mixed models, breath CIR increased by AS consumed 1-4 h before sample collection, AP consumed 3-6 h before sample collection, and 15-d intakes of AS and AP, all with similar effect sizes. The breath CIR was also inversely associated with 15-d intakes of intrinsic sugars and plant protein; thus, associations with 15-d intakes were particularly strong when expressed proportionally as the AS ratio (added sugars/total sugars) and AP ratio (animal protein/total protein).

CONCLUSIONS

The breath CIR is a promising measure of long-term intakes of AS and AP, especially as proportional intakes. Approaches to increase specificity would benefit the further development of this biomarker.

The Carbon Isotope Ratio as an Objective Biomarker of Added Sugar Intake: A Scoping Review of Current Evidence in Human Nutrition

Objective biomarkers of dietary intake are needed to advance nutrition research. The carbon isotope ratio (C13/C12; CIR) holds promise as an objective biomarker of added sugar (AS) and sugar-sweetened beverage (SSB) intake. This systematic scoping review presents the current evidence on CIRs from human studies. Search results (through April 12, 2024) yielded 6297 studies and 24 final articles. Studies were observational (n = 12), controlled feeding (n = 10), or dietary interventions (n = 2). CIRs were sampled from blood (n = 23), hair (n = 5), breath (n = 2), and/or adipose tissue (n = 1). Most (n = 17) conducted whole tissue (that is, bulk) analysis, 8 used compound specific isotope analysis (CSIA), and/or 2 studies used methods appropriate for analyzing breath. Studies were conducted in 3 concentrated geographic regions of the United States (n = 7 Virginia; n = 5 Arizona; n = 4 Alaska), with only 2 studies conducted in other countries. Studies that used CSIA to examine the CIR from the amino acid alanine (CIR-Ala; n = 4) and CIR analyzed from breath (n = 2) provided the most robust evidence for CIR as an objective biomarker of AS and SSBs (R2 range 0.36-0.91). Studies using bulk analysis of hair or blood showed positive, but modest and more variable associations with AS and SSBs (R2 range 0.05-0.48). Few studies showed no association, particularly in non-United States populations and those with low AS and SSB intakes. Two studies provided evidence for CIR to detect changes in SSB intake in response to dietary interventions. Overall, the most compelling evidence supports CIR-Ala as an objective indicator of AS intake and breath CIR as an indicator of short-term AS intake. Considering how to adjust for underlying dietary patterns remains an important area of future work and emerging methods using breath and CSIA warrant additional investigation. More evidence is needed to refine the utility and specificity of CIRs to measure AS and SSB intake.

Discerning animal-sourced food in diet using isotope analysis of human scalp hair and fingernails

PURPOSE

Diet-related diseases are advancing as the leading cause of death globally. As self-reporting of diet by patients can be associated with errors, stable isotopes of human tissues can be used to diagnose diseases, understand physiology, and detect change in diet. This study investigates the effect of type and amount of food on the nitrogen and carbon concentration (Nconc and Cconc) and isotopic composition (δ15N and δ13C) in human scalp hair and fingernails.

METHODS

A total of 100 residents participated in the study whereas only 74 individuals provided complete diet history. Sixty-six food items majorly available to them were also collected. The Nconc, Cconc, δ15N and δ13C values of human hair, nails and food items were determined.

RESULTS

The Nconc, Cconc, δ15N and δ13C values between plant-sourced and animal-sourced food items, as well as human hair and nail tissue were significantly different (p < 0.05). The δ15N value of human tissues was distinct between lacto-vegetarians and omnivores by 0.9‰. The δ15N and δ13C values of human tissues increased by 0.4-0.5‰ with every 5% increase in the consumption of animal protein.

CONCLUSIONS

The study helps to demarcate lacto-vegetarians from omnivores, and estimate the percentage of animal protein in diet based on the dual isotope values of human tissues. It also acts as a reference to determine isotopic composition of hair tissue provided the isotope value of nail tissue is known and vice versa.

Comparison of Total Body Vitamin A Stores Using Individual versus Population 13C-Natural Abundance of Serum Retinol in Preschool Children and Women Residing in 6 Diverse African Countries

BACKGROUND

Stable isotope techniques using 13C to assess vitamin A (VA) dietary sources, absorption, and total body VA stores (TBSs) require determination of baseline 13C abundance. 13C-natural abundance is approximately 1.1% total carbon, but varies with foods consumed, supplements taken, and food fortification with synthetic retinyl palmitate.

OBJECTIVES

We determined 13C variation from purified serum retinol and the resulting impact on TBSs using pooled data from preschool children in Burkina Faso, Cameroon, Ethiopia, South Africa, Tanzania, and Zambia and Zambian women.

METHODS

Seven studies included children (n = 639; 56 ± 25 mo; 48% female) and one in women (n = 138; 29 ± 8.5 y). Serum retinol 13C-natural abundance was determined using GC-C-IRMS. TBSs were available in 7 studies that employed retinol isotope dilution (RID). Serum CRP and α1-acid-glycoprotein (AGP) were available from 6 studies in children. Multivariate mixed models assessed the impact of covariates on retinol 13C. Spearman correlations and Bland-Altman analysis compared serum and milk retinol 13C and evaluated the impact of using study- or global-retinol 13C estimates on calculated TBSs.

RESULTS

13C-natural abundance (%, median [Q1, Q3]) differed among countries (low: Zambia, 1.0744 [1.0736, 1.0753]; high: South Africa, 1.0773 [1.0769, 1.0779]) and was associated with TBSs, CRP, and AGP in children and with TBSs in women. 13C-enrichment from serum and milk retinol were correlated (r = 0.52; P = 0.0001). RID in children and women using study and global estimates had low mean bias (range, -3.7% to 2.2%), but larger 95% limits of agreement (range, -23% to 37%).

CONCLUSIONS

13C-natural abundance is different among human cohorts in Africa. Collecting this information in subgroups is recommended for surveys using RID. When TBSs are needed on individuals in clinical applications, baseline 13C measures are important and should be measured in all enrolled subjects.

Carbon Isotope Ratios of Plasma and RBC Fatty Acids Identify Meat Consumers in a 12-Week Inpatient Feeding Study of 32 Men

BACKGROUND

Molecular stable isotope ratios are a novel type of dietary biomarker with high sensitivity and specificity for certain foods. Among these, fatty acid carbon isotope ratios (CIRs) have strong potential but have not been investigated as dietary biomarkers.

OBJECTIVES

We evaluated whether fatty acid CIRs and mass proportions were associated with meat, fish, and sugar-sweetened beverage (SSB) intake.

METHODS

Thirty-two men [aged 46.2 ± 10.5 y; BMI (kg/m2): 27.2 ± 4.0] underwent a 12-wk inpatient dietary intervention at the National Institute of Diabetes and Digestive and Kidney Diseases in Phoenix, Arizona. Men were randomly assigned to 1 of 8 dietary treatments varying the presence/absence of dietary meat, fish, and SSBs in all combinations. Fatty acid CIRs and mass proportions were measured in fasting blood samples and adipose tissue biopsies that were collected pre- and postintervention. Dietary effects were analyzed using multivariable regression and receiver operating characteristic AUCs were calculated using logistic regression.

RESULTS

CIRs of the several abundant SFAs, MUFAs and arachidonic acid (20:4n-6) in plasma were strongly associated with meat, as were a subset of these fatty acids in RBCs. Effect sizes in plasma ranged from 1.01‰ to 1.93‰ and were similar but attenuated in RBCs. Mass proportions of those fatty acids were not associated with diet. CIRs of plasma dihomo-γ-linolenic acid (20:3n-6) and adipose palmitic acid (16:0) were weakly associated with SSBs. Mass proportions of plasma odd-chain fatty acids were associated with meat, and mass proportions of plasma EPA and DHA (20:5n-3 and 22:6n-3) were associated with fish.

CONCLUSIONS

CIRs of plasma and RBC fatty acids show promise as sensitive and specific measures of dietary meat. These provide different information from that provided by fatty acid mass proportions, and are informative where mass proportion is not. This trial is registered at www.clinicaltrials.gov as NCT01237093.

Stable isotope ratios of nitrogen and carbon as biomarkers of a vegan diet

PURPOSE

Dietary biomarkers can potentially overcome the limitations of self-reported dietary data. While in ecology and archaeology, stable isotope ratios of carbon and nitrogen are widely used as biomarkers, this is not the case in nutrition research. Since the abundance of the 13C and the 15N isotope differ in food sources from plant and animal origin, stable isotope ratios of carbon and nitrogen (δ13C and δ15N) may differ in human biological material. Here, we investigated the stable isotope ratios of nitrogen and carbon in serum and urine from vegans and omnivores.

METHOD

Measurement of δ15N and δ13C in serum and 24 h urine was performed by Elemental Analyzer-Isotope Ratio Mass Spectrometer in the cross-sectional study "Risks and Benefits of a Vegan Diet". The study included 36 vegans and 36 omnivores with a median age of 37.5 years (matched for age and sex), who adhered to their diet for at least 1 year.

RESULTS

Both δ15N and δ13C were significantly lower in both the serum and 24 h urine of vegans compared to omnivores. δ15N either in serum or urine had 100% specificity and sensitivity to discriminate between vegans and omnivores. Specificity of δ13C was also > 90%, while sensitivity was 93% in serum and 77% in urine.

CONCLUSION

δ15N both in serum and urine was able to accurately identify vegans and thus appears to be a promising marker for dietary habits.

Evaluating a Model of Added Sugar Intake Based on Amino Acid Carbon Isotope Ratios in a Controlled Feeding Study of U.S. Adults

Previous studies suggest that amino acid carbon stable isotope ratios (CIRAAs) may serve as biomarkers of added sugar (AS) intake, but this has not been tested in a demographically diverse population. We conducted a 15-day feeding study of U.S. adults, recruited across sex, age, and BMI groups. Participants consumed personalized diets that resembled habitual intake, assessed using two consecutive 7-day food records. We measured serum (n = 99) CIRAAs collected at the end of the feeding period and determined correlations with diet. We used forward selection to model AS intake using participant characteristics and 15 CIRAAs. This model was internally validated using bootstrap optimism correction. Median (25th, 75th percentile) AS intake was 65.2 g/day (44.7, 81.4) and 9.5% (7.2%, 12.4%) of energy. The CIR of alanine had the highest, although modest, correlation with AS intake (r = 0.32, p = 0.001). Serum CIRAAs were more highly correlated with animal food intakes, especially the ratio of animal to total protein. The AS model included sex, body weight and 6 CIRAAs. This model had modest explanatory power (multiple R2 = 0.38), and the optimism-corrected R2 was lower (R2 = 0.15). Further investigations in populations with wider ranges of AS intake are warranted.