Metabolomic profiles as reliable biomarkers of dietary composition

Abstract

Background: Clinical nutrition research often lacks robust markers of compliance, complicating the interpretation of clinical trials and observational studies of free-living subjects.Objective: We aimed to examine metabolomics profiles in response to 3 diets that differed widely in macronutrient composition during a controlled feeding protocol.Design: Twenty-one adults with a high body mass index (in kg/m2; mean ± SD: 34.4 ± 4.9) were given hypocaloric diets to promote weight loss corresponding to 10-15% of initial body weight. They were then studied during weight stability while consuming 3 test diets, each for a 4-wk period according to a crossover design: low fat (60% carbohydrate, 20% fat, 20% protein), low glycemic index (40% carbohydrate, 40% fat, 20% protein), or very-low carbohydrate (10% carbohydrate, 60% fat, 30% protein). Plasma samples were obtained at baseline and at the end of each 4-wk period in the fasting state for metabolomics analysis by using liquid chromatography-tandem mass spectrometry. Statistical analyses included adjustment for multiple comparisons.Results: Of 333 metabolites, we identified 152 whose concentrations differed for ≥1 diet compared with the others, including diacylglycerols and triacylglycerols, branched-chain amino acids, and markers reflecting metabolic status. Analysis of groups of related metabolites, with the use of either principal components or pathways, revealed coordinated metabolic changes affected by dietary composition, including pathways related to amino acid metabolism. We constructed a classifier using the metabolites that differed between diets and were able to correctly identify the test diet from metabolite profiles in 60 of 63 cases (>95% accuracy). Analyses also suggest differential effects by diet on numerous cardiometabolic disease risk factors.Conclusions: Metabolomic profiling may be used to assess compliance during clinical nutrition trials and the validity of dietary assessment in observational studies. In addition, this methodology may help elucidate mechanistic pathways linking diet to chronic disease risk. This trial was registered at clinicaltrials.gov as NCT00315354.

Keywords: cardiometabolic risk factors; dietary compliance; dietary composition; glycemic index; low-carbohydrate diet; low-fat diet; metabolomics; obesity.

© 2017 American Society for Nutrition.

Figures

FIGURE 1

Patterns of metabolite response to diet. Examples of 8 metabolites demonstrating significant differential responses to 3 weight-loss maintenance diets administered to 21 young adults in a randomized crossover trial. Metabolites were selected to illustrate contrasting patterns of responses. Vertical axes show relative change from pre–weight loss metabolite concentration. Boxes indicate means and 95% CIs. Lines connect covariate-adjusted data for individual participants, omitting outliers detected by robust regression procedure. Bracketed diets did not differ significantly according to repeated-measures ANOVA on log-transformed, covariate-adjusted metabolite concentrations. P tests the hypothesis of equal mean concentration across all 3 diets, adjusted for multiple comparisons by Holm step-down procedure. Adj, adjusted; LF, low-fat diet; LGI, low–glycemic index diet; TAG, triacylglycerol; VLC, very–low carbohydrate diet.

FIGURE 2

Accuracy of diet classification according to metabolite profile. For each sample, the data from that sample was withheld, and a Bayesian network classifier was constructed from the metabolite profile data among the remaining samples. Then, the classifier was used to predict which diet had been consumed when the withheld sample was obtained. Samples are plotted based on their position relative to the 2 principal components that capture the most variation in the metabolite profiling data for each classifier. Colors indicate the actual diet corresponding to each sample (LF, black; LGI, gray; VLC, white), and shapes indicate the classifier prediction by the classifier (LF, square; LGI, round; VLC, triangle). Misclassified samples are circled. LF, low-fat diet; LGI, low–glycemic index diet; VLC, very–low carbohydrate diet.