Attenuation of Adaptive Thermogenesis by a Culinary Dose of Red Pepper During 24-Hour Negative Energy Balance

Obesity treatment requires weight loss through a negative energy balance (EB) followed by sustained weight maintenance. Adaptive thermogenesis, increased hunger, and decreased fullness challenge long-term success. Capsaicin, the pungent principle in red pepper (RP), has been reported to modestly increase energy expenditure (EE) and fat oxidation (lower respiratory quotient [RQ]) while reducing energy intake (EI). This article updates a previous review and meta-analyses (1995-2010), incorporating studies published through 2024, to evaluate whether culinary RP doses can attenuate adaptive thermogenesis and decreased fullness during negative EB. Twenty-two publications representing 24 randomized controlled studies were synthesized. Meta-analyses assessed EE and RQ differentiated by duration, dose, EB status, and protein level. One-meal studies showed that EE (diet-induced thermogenesis) and RQ changes did not reach statistical significance. Long-term studies revealed that EE changes did not reach statistical significance, whereas RQ was consistently lower, indicating enhanced fat oxidation. Appetite and EI findings were mixed. Designs were heterogenous and possibly too short to capture sustained effects or too long to ensure adherence. To address these limitations, we incorporated 24-hour controlled respiratory chamber studies comparing capsaicin and capsaicin combined with elevated protein vs placebo across all 3 meals, in both neutral and negative EB. Meta-analyses showed that EE increases during negative EB did not reach statistical significance overall, although individual studies suggest that capsaicin may modestly increase EE compared with placebo. Capsaicin significantly reduced RQ in negative-EB and in high-protein conditions, indicating greater fat oxidation. Capsaicin also counteracted decreased fullness during negative EB. Culinary RP doses do not fully prevent adaptive thermogenesis but may attenuate its impact during negative EB, particularly when paired with protein. Enhanced fat oxidation and improved fullness indicate potential benefits for weight-loss maintenance. Long-term EE effects remain minimal, but sustained RQ reductions support capsaicin as an adjunct to dietary weight-loss maintenance strategies.