Heat = energy. As your body gives off heat, it's losing energy, which ultimately comes from the food you eat. Thus, the more thermogenesis you have going on in your body, the less likely you are to get fat.
Dr. Moritani at Kyoto University has developed a technology for measuring the thermogenic effect of substances such as capsaicin (the hot element in cayenne peppers) and caffeine.
Moritani's group gave young men a caffeine capsule (300 mg, swallowed with 100 ml of water) or a placebo capsule 2 hours before performing low-intensity cycling. Those receiving caffeine burned more fat during exercise than those taking the placebo pill.
Great! So 300 mg of caffeine taken before working out may speed up your fat-burning "engines." But will less work?
Yes. In assessing the research on this matter, researchers concluded that a single dose of at least 100 mg of caffeine is needed to boost thermogenesis for 1-2 hours or more. Taking even more (600-1000 mg/day) can increase 24-hour metabolic (calorie-burning) rate.
Will coffee do the same thing? Don't count on it. As Dr. Moritani and researchers point out, coffee doesn't produce the same fat-burning effects. This may be due to substances in coffee that "neutralize" caffeine.
To intensify the fat-burning and performance-enhancing benefits of caffeine, look for a supplement that combines caffeine with extracts of green tea leaf and bitter orange (Citrus aurantium).