Since every mall now has a kiosk selling "metabolic enhancers" of one kind or another, it's time to take a fresh look at exactly what these babies are and what they can -- and cannot -- do.

What about the stuff they sell in those kiosks?

Well, primarily these are thermogenic agents. A thermogenic agent is one that produces heat -- in everyday parlance, it "speeds up" the metabolism. The kiosk products do indeed produce some thermogenic effect, but at a cost.

The most common ingredient in metabolic enhancers is ephedra. Ephedra is basically legal "speed." While I'd be lying if I said it's as dangerous as crack cocaine, a small dose is approximately equal to a few cups of strong coffee. Same deal with ma huang. These substances should be avoided like the Black Plague if you have any tendency at all to high blood pressure. They can -- and usually do -- make you jittery, nervous and speedy, and can raise blood pressure and heart rate. This does indeed temporarily "speed up" the metabolic rate, but how much that transfers to actual weight loss is anyone's guess. My personal opinion is that to whatever extent they work, they do so by suppressing your appetite, NOT by adding appreciably to the number of calories burned during the day, though they probably do slightly increase the number of calories burned while "under the influence."

Understanding your metabolism

What is metabolism anyway? One clever writer (Kenneth Baum, author of Metabolize!) asked his six-year-old son that question and was met with the following answer: "It's everything that happens from when you eat to when you poop!" And you know what? That's not a bad definition. Metabolism is, briefly, the sum total of everything that happens in the body -- the building up of various substances (muscle, proteins, RNA, hair, nails, enzymes, storage fat, bones) and the breaking down of others (food, storage fat, etc.). Both "building up" processes (called anabolic) and "breaking down" processes (catabolic) are going on simultaneously, all the time. And the raw material, the stuff the body uses for this myriad of tasks, is food. Or, more properly, the nutrients contained in food.