The hot and spicy taste of cayenne pepper comes from capsaicin, a compound found in many hot peppers. Capsaicin is known to boost metabolism, causing the body to produce extra heat and burn more calories for fuel. Research suggests that after consuming foods with capsaicin, the body’s metabolic rate (aka energy use) can increase 15 to 20 percent for up to two hours. Other studies suggest capsaicin also increases fat oxidation, allowing the body to better use fat as fuel

Effects of novel capsinoid treatment on fatness and energy metabolism in humans: possible pharmacogenetic implications.RSnitker, S., Fujishima, Y., Shen, H., et al. University of Maryland School of Medicine, Baltimore, MD. The American Journal of Clinical Nutrition. 2009 Jan; 89(1):45-50.

Pharmacokinetic and the effect of capsaicin in Capsicum frutescens on decreasing plasma glucose level. Chaiyasit, K., Khovidhunkit, W., Wittayalertpanya, S. Inter-department of Pharmacology, Graduate School, Chulalongkorn University, Bangkok, Thailand. Journal of the Medical Association of Thailand. 2009 Jan; 92(1):108-13..