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

Abstract

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.

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

“…We also recognize that extensive consumption of C 4 sugars, C 4 -based beverages, and marine protein sources could complicate interpretation of hypotheses 2 and 3 ( 8 , 16 , 23 – 25 , 55 ).…”

“… 19 , 20 ). We recognize that hair is composed of keratin, which contains both essential and nonessential amino acids, with nonessential amino acids derived from either dietary proteins or dietary carbohydrate sources ( 21 – 26 ). However, the bias toward synthesis of proteins from preformed amino acids in dietary proteins results in hair δ 13 C values underestimating the amounts of carbohydrates and fats in human diets ( 22 ).…”

“…While there are many approaches to quantifying dietary choices, carbon (δ 13 C) and nitrogen (δ 15 N) stable isotope ratios of human scalp hair and blood have been shown to directly relate to an individual’s dietary protein sources ( 24 , 25 , 39 – 43 ). We also recognize that carbon-derived carbohydrates can be incorporated into nonessential amino acids ( 23 – 26 ). The δ 13 C values of human hair reveal the proportion of protein originating from C 3 plants or C 4 plants in an individual’s diet ( 16 , 44 – 47 ).…”

Effect of Organic Food Intake on Nitrogen Stable Isotopes

“…When organic plants are consumed and poultry is the main source of animal proteins, increasing proportional intake of plant proteins makes the body δ 15 N closer to that of meat and fish, while it is the opposite when animal proteins are predominantly from an aquatic origin ( Figure S1 ). This reemphasizes that the capacity of δ 15 N as biomarker for meat and fish intake [ 1 , 2 ] is very contextual. Furthermore, these opposite δ 15 N behaviors between the two modeled dietary scenarios ( Figure S1 ) show that the directionality of the error that ranges between 0‰ and Δ 15 N org-conv ( Figure S2 , Equation (3)) depends on the difference in δ 15 N between dietary plants and animals.…”

“…Biomarkers for the intake of plant and animal proteins can help us to understand relationships between diet and health, and to assess adherence to nutritional interventions aiming at modulating reliance on animal and plant proteins. The natural abundance of the stable isotopes of nitrogen (δ 15 N) is increasingly viewed as a biomarker for meat and fish intake [ 1 , 2 , 3 , 4 , 5 ]. Recent controlled feeding studies found associations between tissue δ 15 N and meat and fish intake [ 1 , 2 ], reinforcing the potential of δ 15 N as a dietary intake biomarker.…”