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

This week we will discuss whether there are things you can do to spend more time sitting on your ashcan. That is not the word the late George Carlin would have used. But even in the Health section, where unmentionable things are often displayed in detail, there are rules.

Why bring this up?

Because the fitness, diet and food industries barrage us with claims about methods or products or substances that "boost metabolism" and thus cause the body to use more calories even at rest. Whether it's the new secret-formula "fat burning" supplement, the "miracle" of green tea (or the Coca-Cola company's effort to capitalize on that with a green tea-based soft drink), or even the sometimes exaggerated claims for the metabolism-boosting benefits of exercise, this is the health equivalent of money for nothing -- a free lunch promise that would, if true, liberate us for more time on the Barcalounger.

Don't count on it.

One thing seems pretty clear from my own fitful experience: To a certain degree, we are what we are. Sure, you can improve the shape and composition of your body with diet and exercise. As you become more fit, you function more efficiently and become able to do more. Your muscles store more fuel and become stronger, your circulatory system gets better at processing oxygen, your resting heart rate and blood pressure might drop, and you can tap different energy systems and sources more effectively.

But the pace and extent of those changes -- the underlying way in which our bodies react and adapt to stress -- is pretty tightly circumscribed. We all know people who seem to eat and drink what they want without gaining an ounce, or who seem to easily add muscle or shave time off of their 10K pace; others of us need to work a lot harder to keep things in balance or make progress.

For those in the great mass called "average," it also seems the case that when the activity stops, some of the more widely advertised benefits taper pretty quickly as well.

Advocates of strength training in particular argue that building more muscle through exercise increases your resting metabolic rate: the number of calories the body uses at rest simply to sustain itself. The higher rate will act, they say, as an automatic form of weight control.

Well, yes, to support the extra muscle the body will use more calories all day long. But how many?

The textbooks are cautious.

Sharon Plowman and Denise Smith, in their introductory text "Exercise Physiology for Health, Fitness and Performance," write that studies of the effect of strength training on resting metabolism "are not definitive." The difference between a bit of extra fat and a bit of extra muscle might come down to just a few calories a day.

Although there are plenty of good reasons to lift weights or do other resistance training (think walk vs. walker), the "transform your metabolism" pitch may be a bit oversold, particularly given the difficulty of adding those extra pounds of muscle.