A fat burner is a substance that encourages the body's metabolism to increase, that provides energy and may even suppress the appetite.
The idea behind them is this: the body burns calories all the time, even when you're just sitting in your chair. A fat burner increases your metabolism – which is like cranking up the idle speed of a car. Fat burners help you run faster, thus burning extra calories each day – whether you're exercising or not.
Ephedra is the name of the most notorious fat burner, which was taken off the market by the FDA a while back. Ephedra proved to be a little too good at revving up the metabolism – so much so that some complained of heart issues, and a few people even died. Today's fat burners are safer and can be used without concern by healthy people.
These are fat burners that use stimulants like caffiene, guarana or yohimbe to elevate the metabolism. Thermogenic fat burners are ephedra-free.
Like the above, but contains no stimulants. This type of fat burner relies on ingredients like green tea extract and grapefruit extract to enhance the body's fat-burning processes. These are ideal fat burners for people who get jittery from stimulants.
Though not fat burners per se, these supplements decrease your body's ability to absorb carbs. That means fewer carbs get stored as fat – preventing fat that otherwise your body would've manufactured.
Fat blockers stop fat from ever being absorbed by tying it up in the digestive system and flushing the fat from your body. These are not fat burners but keep your body from absorbing and storing fat that you eat.
Fat burners shouldn't be subsitituted for exercise and healthy eating. But if you're having trouble meeting your weight loss goals, a fat burner might be for you. Talk to your doctor, give one a try, and good luck. Stay healthy!