Stable isotope analyses show that Ancient Beringian diets were seasonally structured and included substantial summer salmon.

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. We assessed the responses of plasma and RBC CIR_AA's to SSB and meat intake in a 12-wk inpatient feeding study. 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 CIR_AA'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 (CIR_NEAA's) and 4 essential AAs (CIR_EAA's) were analyzed using multivariable regression. In plasma, 4 of 5 CIR_NEAA's increased with SSB intake. Of these, the CIR_Ala 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 CIR_NEAA's increased with SSBs but had smaller effect sizes than in plasma. All plasma CIR_EAA's increased with meat intake (but not SSB or fish intake), and the CIR_Leu 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 CIR_AA's in plasma, but not RBCs, were in equilibrium with the diets by the end of the study. The results of this study in men support CIR_NEAA's as potential biomarkers of SSB intake and suggest CIR_EAA's as potential biomarkers of meat intake in US diets. This trial was registered at clinicaltrials.gov/ct2/show/NCT01237093 as NCT01237093.

The natural abundance nitrogen stable isotope ratio (NIR) of whole tissue correlates with animal protein intakes, including meat and fish. Amino acid (AA) NIRs (NIR_AAs) are more variable than the whole-tissue NIRs and may thus better differentiate among foods. We evaluated whether NIR_AAs were associated with intakes of fish and meat and whether these dietary associations were larger than with whole-tissue NIRs. 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 NIR_AAs (free and protein-bound) were measured as secondary outcomes in 32 participants. Multivariable regression was used to determine responses of postintervention NIR_AAs to dietary variables, and logistic regression was used to calculate receiver operating characteristic AUCs. Most plasma NIR_AAs increased with fish and meat intakes, but to a greater extent with fish intake. The largest increase in response to fish intake was plasma NIR_Leucine (β = 2.19, SE = 0.26). The NIR_Threonine decreased with both fish and meat intakes. Fewer RBC NIR_AAs increased with fish intake, and only RBC NIR_Proline increased with meat intake. No plasma or RBC NIR_AA responded to SSB intake. We identified fish intake with a high degree of accuracy using plasma NIR_Leucine (corrected AUC, cAUC = 0.96) and NIR_{Glutamic acid/glutamine} (cAUC = 0.93), and meat intake to a lower degree using plasma NIR_Proline (cAUC = 0.80) and RBC NIR_Proline (cAUC = 0.85). Plasma and RBC NIR_AAs 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.

Previous studies suggest that amino acid carbon stable isotope ratios (CIR_AAs) 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) CIR_AAs 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 CIR_AAs. 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 CIR_AAs 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 CIR_AAs. 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.

The alanine carbon isotope ratio (Ala CIR) biomarker was positively associated with added sugar (AS) and sugar-sweetened beverage (SSB) intake in multiple studies from the USA. Association strengths varied, and Ala CIR was also correlated with protein source in certain studies. To examine Ala CIR associations with AS and SSB intake and animal protein ratio (animal protein/total protein, APR), and adjustment for APR, by pooling data from 4 previous studies. We pooled diet and biomarker data from 4 studies (n=346). These included a cross-sectional study of Yup'ik Alaska Native adults (n=62), a 12-wk randomized controlled feeding study in men (n=32), a 2-wk habitual intake controlled feeding study in postmenopausal women (n=153), and a 15-d habitual intake controlled feeding study of adults (n=99). We estimated correlations between amino acid CIRs and diet, and performed multivariable regression of Ala CIR on standardized intake variables to determine simultaneous associations with AS (g/d) or SSBs (servings/d) and APR. We included study by intake interactions to allow for heterogeneity among studies. We then ran models where leucine (Leu) CIR was included to adjust for APR. There were positive correlations (95% CIs) between Ala CIR and AS intake [r=0.54 (0.46, 0.61)], log-SSB intake [r=0.63 (0.56, 0.69)], and APR [r=0.32 (0.22, 0.41)]. Study-specific slopes for the relationship between Ala CIR and AS or SSB intake were similar in models with and without adjustment for APR. Across studies, slopes ranged from 0.34 (0.08, 0.61) to 1.75 (1.29, 2.20) for AS intake in models with APR and from 0.35 (0.01, 0.68) to 1.11 (0.81, 1.40) for SSB intake in models with APR. Replacing APR with Leu CIR resulted in similar slopes between Ala CIR and AS/SSB intake. The Ala CIR is a robust biomarker of AS/SSB intake. Potential associations with APR can be adjusted for using a simultaneously-measured biomarker. (DBD study) clinicaltrials.gov/NCT01237093; (NPAAS) clinicaltrials.gov/NCT00000611.