Stability of human plasma “metabotypes” in response to dietary challenges

Introduction and Objective – Metabolic phenotyping in humans is usually done in fasting state not taking into account that metabolism is highly dynamic with major changes in space (organs) and time. To assess this flexibility of the human metabolic system we performed standardized challenge tests combined with metabolite profiling of plasma and tissues as part of the NutriTech project.Methods – 72 volunteers (men and women, age = 60±3 yrs., BMI = 30±2 kg/m²) were recruited, submitted to whole body MRI and underwent an oral glucose tolerance test (OGTT) and a mixed meal tolerance test (MMTT). The two tests were repeated after 13 weeks with 40 volunteers on a diet providing 20 % less calories, while 32 followed a standardized diet without energy restriction. Metabolite profiling was performed in plasma samples using LC-MS/MS, GC-MS and NMR platforms with around 260 entities covered. Results – Despite a mean weight loss of 4.5±0.2 kg, caloric restriction did not induce major changes in plasma metabolite concentration profiles during the challenge tests. Assessed by ANOVA, the overall contribution of the caloric restriction to the observed variations of metabolite concentrations was negligible, ranging from 0.25% for lyso PC C18:2, to about 2.3% for Alanine. This indicates the individual responses to the challenges were highly reproducible on the two occasions, identifying “robust metabotypes”. Despite little effect of the intervention, inter-individual variability is extremely high. Taking all metabolites analyzed into consideration, on average inter-individual differences account for more than 50% of the observed variability; ranging from 10% for non-esterified fatty acids to more than 80% for cholesterol in VLDL particles. Conclusion – The results demonstrate that on a time axis of three months, metabolic phenotypes derived from challenge experiments such as OGTT or MMTT are highly reproducible despite large inter-individual differences