Lightning in a (Spice) Bottle: What It Is
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  .
But don't just down spices and expect the pounds to melt away. The amount of capsaicin in cayenne is relatively small and won't carry far beyond that two-hour metabolic boost. A more significant effect of cayenne is appetite suppression. It turns out the capsaicin in readily-edible amounts of spice might be enough to help cut cravings for fatty, salty, and sweet foods. Muy muy caliente!
Add Some Pep(per) To Your Step: What It Means to You
Eater beware: this hot item comes with some words of caution. Cayenne pepper can decrease the effectiveness of some common medications like aspirin, blood thinning drugs, and antacids. People with latex, banana, avocado, kiwi, or chestnut allergies may also be allergic to cayenne pepper.