BACKGROUND: The thermogenic and metabolic properties of capsinoids appear to mimic those of the more pungent sister compound capsaicin. However, few data exist on how capsinoid ingestion affects energy expenditure in humans and no data exist on its interaction with exercise. We aimed to determine how ingestion of capsinoids affected energy expenditure, lipid oxidation and blood metabolites at rest and during moderate intensity exercise. METHODS: Twelve healthy young men (age = 24.3 +/- 3 yr, BMI = 25.5 +/- 1.7 kg.m-2) were studied on two occasions in a double-blind design following ingestion of either placebo or 10 mg of purified capsinoids at rest, after 90 min of cycling at 55% VO2 peak, and for 30 min into recovery. Subjects ingested the capsules 30 min prior to exercise. RESULTS: At rest, following ingestion of capsinoids, we observed increases in VO2 and plasma norepinephrine levels, and decreases in concentrations of serum free fatty acids, plasma glycerol and the respiratory exchange ratio (all P < 0.05). At exercise onset, we observed a blunted accumulation of blood lactate with capsinoid ingestion vs. placebo (P < 0.05). There were no other significant differences between the conditions during or post-exercise. CONCLUSION: The ingestion of 10 mg of capsinoids increased adrenergic activity, energy expenditure, and resulted in a shift in substrate utilization toward lipid at rest but had little effect during exercise or recovery. The changes we observed confirm previous data on the thermogenic and metabolic effects of capsinoids at rest and further promote its potential role as an adjunct weight loss aid, in addition to diet and exercise.