Background: Capsaicin, which is naturally found in chili peppers, has been shown to increase energy expenditure and fat oxidation, possibly through sympathetic nervous system stimulation or catecholamine release. However, the pungency of capsaicin limits its use in many individuals. Dihydrocapsiate is a less-pungent thermogenic capsinoid that is related to capsaicin. Previous research on the effect of capsinoid supplements on energy metabolism and the potential thermogenic and fat-burning effect has been mixed. Preclinical studies have demonstrated a thermogenic effect of capsinoids in mice; however, human studies have been inconclusive.

Hypothesis/purpose of study: To determine whether dihydrocapsiate has acute or chronic effects on resting metabolic rate (RMR)

Subjects: Healthy nonsmoking men (N = 78) who had not exercised more than twice a week for the past 6 months, were not dieting or taking weight loss supplements, and who had not participated in regular resistance exercise were included.

Experimental design:Randomized, double-blind, parallel arm trial

Treatments and protocol:All testing was performed at baseline and at day 28. After an overnight fast, RMR was measured by indirect calorimetry for 45 minutes before and for 120 minutes after ingestion of dihydrocapsiate or placebo. Volunteers received 0 mg (placebo), 3 mg, or 9 mg dihydrocapsiate/day for 28 days. Changes in energy substrate oxidation were assessed by monitoring urinary nitrogen excretion. Acute effects were calculated by comparing post-ingestion RMR with baseline. Chronic effects of dihydrocapsiate on RMR were calculated from the average 2-hour RMR on day 28 minus baseline RMR. Total body fat was measured by dual energy x-ray absorptiometry. Symptoms and adverse events were assessed by a validated patient questionnaire. Demographics including age, body composition, and exercise history were similar among study arms at baseline.