BACKGROUND: Previous studies have demonstrated that capsaicinoid ingestion can increase lipolysis as measured via breath sample analysis. However, no human studies have included blood measures of catecholamines or markers of lipolysis, in particular while comparing men and women. PURPOSE: To compare blood epinephrine (EPI), norepinephrine (NE), free fatty acids (FFA) and glycerol concentrations before and after ingestion of a placebo or a taste-masked capsaicinoid supplement in men and women. METHODS: Ten men (25±1 yrs) and 10 women (24±1 yrs) ingested a placebo or a supplement (2 mg capsaicinoids) with one week separating conditions. A total of four fasting blood samples were collected from subjects during each visit; following a 30 minute rest period, immediately before placebo or supplement intake (Pre); 2 hours post intake (2 hr); immediately following the cessation of 30 minutes of exercise performed at 65% of maximal heart rate reserve (2.5 hr); 90 minutes following the cessation of exercise (4 hr). Heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure were recorded at all times. RESULTS: Although sex and time effects were noted for HR, SBP, and DBP (p<0.05; all higher for men compared to women; HR and SBP higher at 2.5 hr compared to Pre; DBP lower at 2.5 hr compared to Pre), no differences were noted in these variables between conditions (p>0.05). No condition main effects or condition interactions were noted for EPI, NE, FFA, or glycerol (p>0.05). However, a time effect was noted for all variables (p<0.0001), with values higher than Pre at 2.5 hr for EPI, FFA, and glycerol, and at 2 hr, 2.5 hr, and 4 hr for NE. A sex effect was noted for EPI (p<0.001) with men higher than women, and for FFA and glycerol (p<0.0001), for which women were higher than men. Contrast analysis indicated higher FFA at 2 hr (p=0.0003) and 2.5 hr (p=0.0001) for supplement compared to placebo when using percent change data, with only women contributing to this effect. CONCLUSION: Ingestion of a single low dose (2 mg) capsaicinoid supplement was not associated with any significant increase in EPI, NE, or glycerol compared to placebo. However, an increase in FFA (a marker of lipolysis) was noted, specifically in women. Lastly, no increase in HR, SBP, or DBP was noted with capsaicinoid supplementation. Supported by OmniActive Health Technologies