Want to Burn Calories? Skip the Green Tea and Go for a Run.

AMERICAN IDLE Metabolism boosters, natural or otherwise, won't help if you don't get off the couch. (By Britt Erlanson -- Getty Images)

Strength training is great for the body and great for long-term health. But "can we say that every additional pound of muscle burns X amount of calories? It is very hard to separate it," said J.C. Santana, director of the Institute of Human Performance, a training and research facility in Boca Raton, Fla.

Likewise, there is "afterburn," a concept tossed around casually in gyms and by trainers with the idea that your lunch-hour workout will still be consuming calories during your two-hour commute that evening.

"Excess post-exercise oxygen consumption" -- the formal term of art -- may indeed earn you more calories after leaving the gym, but the benefit is proportionate to the work done. Afterburn occurs when the body accumulates an oxygen deficit during activity -- and that means working beyond the ability of your lungs to keep up. Oxygen deficit is the norm at the start of a workout, until the body is warmed up, but sustaining it over time is hard.

For the modest exerciser, Plowman and Smith estimate that a three-mile jog that consumes 300 calories might produce 30 calories or so of afterburn.

Diet, as might be expected, influences metabolism, but not in the way that the magic supplement or herb pitchmen might lead you to believe. Although some foods (certain spices, caffeinated beverages) do appear to tweak your system, the effect is modest. You can't counteract a Big Mac with a thermos of green tea.

But the energy used to digest food is substantial, accounting for perhaps 10 percent of a person's daily calorie expenditure. What you eat can push that either higher or lower.

Dense, whole grains and vegetables have a higher "thermic effect": They take more calories to digest, along with providing nutrition. Sugary, refined foods, by contrast, carry a triple whammy: They're high in calories, typically low in nutrition and broken down with little effort.

No doubt all of these small contributions add up to a metabolic plus: a few extra calories from muscle, a few from the afterburn, a few from digesting a big bowl of broccoli. But don't count on this alone to turn your body into a high-octane furnace.

There really is no free lunch. Which lets us end where we began: The only sure bet is to get off your . . . well, you know.