Two weeks ago, I introduced you to Greg Ellis, whose new book, Dr. Ellis's Ultimate Diet Secrets (Targeted Body Systems Publishing, $59.95), is to eating and exercising what Moby-Dick is to whaling.

During a power walk, Ellis and I discussed some of the surprising things he's learned over the last 40 years about how the body turns food into energy, muscle and fat.

One of Ellis' favorite sayings is "putting it to the numbers" - his phrase for testing conventional wisdom against scientific fact. By putting it to the numbers, Ellis, 55, who has a doctorate in exercise physiology, has discovered that many accepted truths are myths.

"People don't do their homework," he gripes. "That's how these myths get started and propagated."

A prime example: If you build more muscle, you'll burn lots of calories.

"This one really irks me," Ellis says. "It's the big one, the great myth."

I confess: It's a myth that I, too, have helped propagate. As faithful readers know, I'm a big booster of resistance training - weight lifting for boys and girls, men and women, people of all ages. In this space and in public presentations, I have sung the benefits of pumping iron, including how it helps control weight.

The conventional wisdom: Muscle is metabolically active. It burns calories even when your body is at rest - 50 to 60 calories a day per pound of muscle. Ergo, if you add a pound of muscle, you can burn an additional 350 calories a week, 1,500 calories a month, 18,000 calories a year - the equivalent of 5 pounds of flesh.

In other words, if you gain a pound of muscle, everything else being equal, you can, in a year, shed 5 pounds of flab.

Trouble is, it ain't so.

"Putting it to the numbers" reveals that resting muscle burns a mere tenth of that - about 5 to 6 calories per pound per day, Ellis says. Since every pound of fat burns 2 calories a day, muscle hardly confers a hefty metabolic advantage - a mere 3 to 4 additional calories per pound.

How does this play out in the real world?

Suppose a woman who weighs 150 pounds begins working out, walking two miles a day, lifting weights three times a week. After six months, she manages to shed 18 pounds of flab and gain 6 pounds of muscle.

To feed that new muscle, her body needs 30 calories of food energy a day (6 pounds x 5 calories = 30). But because she has dropped 18 pounds of fat, her energy needs have also dropped - by 36 calories (18 pounds x 2 calories = 36). Result: Despite all that new muscle, she needs to eat 6 calories a day less to maintain her new weight.

Moreover, adding 6 pounds of muscle is no easy feat. When Ellis was working on his doctorate, doing body-composition studies in the lab, he found that the muscle mass of female bodybuilders, compared with that of untrained women, was greater by only 6 pounds.

"Steroid girls had only 8 to 10 pounds more lean body mass," Ellis says. "I'm talking about hard-core bodybuilding chicks - not someone lifting 5-pound dumbbells, but a gal benching 150, and going at it hard."

Ditto for guys. After several years of training hard, a man may be able to gain 10 pounds of muscle, max. Even with steroids and other anabolic aids, the most a competitive bodybuilder can add is 30 to 40 pounds of muscle, Ellis says. At 5 calories per pound of muscle, all that extravagant anabolic gingerbread revs the metabolism by a mere 150 calories - an amount that could be wiped out by a Reese's Peanut Butter Cup.

"So when Diane Sawyer works out with rubber bands and 5-pound dumbbells and manages to add a quarter-pound of muscle, she may be burning more calories through the exercise itself," Ellis says, "but she's doing zip to increase her resting metabolism."

Can Ellis be believed? For proof, he showed me citations and tables from his trusty texts, including a real page-turner titled Energy Metabolism: Tissue Determinants and Cellular Corollaries. But more persuasive than academic data was this argument: "If new muscle burns 50 calories a pound, why doesn't already existing muscle burn 50 calories a pound?" Ellis asks. "How does the body determine that new muscle burns 50 calories, while old muscle burns only 5?"

Answer: It doesn't, because all muscle burns only 5 calories. Putting it to the numbers: If every pound of muscle burned 50 calories, a typical 200-pound man would have a resting metabolic rate (RMR) from muscle alone of 4,000 calories (80 pounds of muscle x 50 = 4,000). Since muscle accounts for about 40 percent of the RMR (organs such as the liver, kidneys, brain and heart account for about 60 percent), the RMR of our hypothetical musclehead would be 10,000 calories - an impossibility. Even Ellis, a mesomorphic pillar of vintage beefcake, has an RMR of only 1,900 calories. So if muscle isn't a calorie-gobbler, why bother to lift weights?

Because, besides making you stronger, fortifying your bones and joints, improving your balance, reducing the risk of heart disease, and giving you a sense of power, control, accomplishment and well-being, pumping iron will make you look better.

"If you add 5 pounds of muscle and lose 5 pounds of fat, the impact on your shape and appearance will be dramatic," Ellis says. "If you add 5 pounds of muscle and lose 10 to 20 pounds of fat, you're definitely going to be eye candy."