Standardization of factors that influence human urine metabolomics

In nutritional metabolomics a large inter- and intra-subject variability exists, and thus, it becomes important to limit the variance introduced by external factors. In a composite controlled study with full provision of all food for the standardized intervention, human urinary metabolite profiles were investigated for different factors, such as handling of urine collections, diet standardization, diet culture, cohabitation and gender. In study A, 8 healthy subjects (4 men; 4 women) collected 24-h urine, splitting each void into two specimens stored either at 4°C or at room temperature. In study B, 16 healthy subjects (7 men; 9 women) collected 24-h urine for three days while being on a standardized diet. Samples were analyzed by 1H NMR and chemometrics. The NMR profiles indicated the presence of metabolites presumably originating from bacterial contamination in 3 out of 16 sample collections stored at room temperature. On the contrary, no changes in the NMR profiles due to contamination occurred in the 24-h urine samples stored at 4°C. The study also showed a trend towards a reduced inter- and intra-individual variation during 3 days of diet standardization. In study A, the urine metabolome showed a clear effect of diet culture and cohabitation, but these effects significantly attenuated after diet standardization (study B). Besides, gender-specific differences were found in both studies. Our results emphasize that best practice for any metabolomic study is a standardized, chilled sample collection procedure, and recommend that diet standardization is performed prior to dietary interventions in order to reduce intra- and inter-subject variability. © 2010 Springer Science+Business Media, LLC

Thermic effect of a meal and appetite in adults: an individual participant data meta-analysis of meal-test trials

Background: Thermic effect of a meal (TEF) has previously been suggested to influence appetite. Objective: The aim of this study was to assess whether there is an association between appetite and TEF. Second, to examine whether protein intake is associated with TEF or appetite. Design: Individual participant data (IPD) meta-analysis on studies were performed at the Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark. Five randomized meal-test studies, with 111 participants, were included. The included studies measured energy expenditure (EE) in respiration chambers and pre- and postprandial appetite sensations using Visual Analog Scales (VAS). The primary meta-analysis was based on a generic-inverse variance random-effects model, pooling individual study Spearman's correlation coefficients, resulting in a combined r-value with 95% confidence interval (95% CI). The I2 value quantifies the proportion (%) of the variation in point estimates due to among-study differences. Results: The IPD meta-analysis found no association between satiety and TEF expressed as the incremental area under the curve (TEFiAUC) (r=0.06 [95% CI −0.16 to 0.28], P=0.58; I2=15.8%). Similarly, Composite Appetite Score (CAS) was not associated with TEFiAUC (r=0.08 [95% CI −0.12 to 0.28], P = 0.45; I2=0%). Posthoc analyses showed no association between satiety or CAS and TEF expressed as a percentage of energy intake (EI) (P>0.49) or TEF expressed as a percentage of baseline EE (P>0.17). When adjusting for covariates, TEFiAUC was associated with protein intake (P=0.0085). Conclusions: This IPD meta-analysis found no evidence supporting an association between satiety or CAS and TEF at protein intakes ∼15 E% (range 11–30 E%)