The prevalence of overweight and obesity is rapidly increasing worldwide and even a low to middle income country like India has succumbed to this. There are multiple etiologies to excess accumulation of fat, among all, positive energy balance due to excess energy intake or reduced physical activity and body’s inability to oxidize fat based on its availability and demand, also known as metabolic inflexibility, tends to be the leading risk factors. The present study was aimed to first measure the intra- and inter-individual variability in nocturnal fat oxidation among young male adults. And second was to examine the effects of four dietary bioactive compounds namely, epigallocatechin-3-gallete (EGCG), caffeine, capsaicin and cinnamaldehyde, on nocturnal energy expenditure (EE) and fat oxidation among young male adults.

The variability in nocturnal fat oxidation was measured using whole-body indirect calorimetry (WBIC). The participants were randomly assigned to receive two different durations of adaptation diet: 3-day (n=5) or 1-day (n=4) dietary adaptation group. Each participant was studied on two separate occasions carried out within 1-week to measure intra-individual variability in nocturnal fat oxidation. The data from all participants were used to calculate inter-individual variability in nocturnal fat oxidation. For the second part of the study, a double-blind, placebo-controlled, randomized controlled trial study design was followed. From a total 19 screened participants, only 9 enrolled for this part of the study. A single dose of the compounds was given to the participants and dose were as follows: EGCG at 300 mg, caffeine at 200 mg, capsaicin at 7.5 mg and cinnamaldehyde at 70 mg. The placebo contained equivalent amounts of bread crumbs. Each dose was weighed in a cellulose-based capsules by the third party to ensure blinding. Each participant was studied on five separate occasions after 3-days dietary adaptation with 1-week wash-out period and carried out within 5-6 weeks. The nocturnal EE and fat oxidation were compared between placebo and interventions.

The intra- and inter-individual variability in nocturnal fat oxidation was lower with 3-day dietary adaptation compared to 1-day dietary adaptation. The intra- inter-individual variability in nocturnal fat oxidation with 3-day dietary adaptation was 4.7% and 7.2%, respectively. The metabolic flexibility to fat oxidation was found to be lower in individuals with high BMI as assessed by the inverse correlation for either ∆RQ or Fed:Fasted RQ with fat oxidation. Among all four dietary bioactive compounds, only caffeine showed promising results with a significant increase in nocturnal EE compared to placebo (+0.2 KJ/min). For nocturnal fat oxidation too, caffeine showed 10% significant increase in nocturnal fat oxidation compared to placebo. Therefore, the increase in EE and fat oxidation and thereby, metabolic flexibility, can be achieved by consuming caffeine, as an adjunct therapy along with dietary and physical activity modifications. However, these findings will need to be confirmed further with larger sample size and across sex and age groups. The use of other dietary bioactive compounds (EGCG, capsaicin and cinnamaldehyde) for the same requires further investigation.