Most of us have heard that sensible weight loss involves some combination of diet and exercise. As a physician, I'm surely not going to tell people to avoid exercise. For most people, exercise is a very healthy thing to do. But when it comes to losing weight, unless we're training for the Olympics, the effect of exercise is minor. What matters most is how many calories go down the hatch.

This bears explaining. Our bodies use the calories we consume to fuel our basic life- processes. The heart needs lots of fuel (calories) to beat its usual 100,000 times in 24 hours. The brain, liver and kidneys also require lots of fuel to perform their many chemical reactions and metabolic tasks. Most of the calories we burn in 24 hours (about 1500 for women and 1800 for men) we would still burn even if we were in a coma.

It's true that working the muscles in our arms, legs and trunk requires fuel (calories) as well, but you'd be amazed how long you would have to row, jog, swim or walk to burn the calories in one slice of cherry pie. (Answer: In order to burn off the 486 calories in a slice of cherry pie a 175-pound person would need to row for 35 minutes, jog for 37 minutes, swim for 41 minutes or walk briskly for 63 minutes.) For most of us it would be more practical to just not eat the pie.

Each of us has a calories-per-day figure for maintaining body weight. If, on the average, we eat that many calories, then we will maintain body weight, neither gaining nor losing. If we consistently eat more calories than our break-even number, then we will gain weight. The unused calories have to be stored somewhere, and will probably go into our body's fat cells. If we consistently eat fewer than our break-even number of calories, then we will lose weight. The body will get its fuel somewhere, and will burn off calories that have been put into storage in fat cells.

This is how it is. We just can't get around the basic biology and physics.

So, if we're trying to lose weight, how do we choose what we do or don't eat? Well, sometimes, our choices are haphazard. A useful analogy concerns shopping. How in the world could we do a good job of shopping without knowing the prices of the items we're putting in our shopping carts? Without knowledge of the prices our choices in merchandise could easily exceed our budgets.

The same holds true when it comes to eating. If we wanted to budget our calories, how in the world could we make good choices if we didn't know the calorie count of the foods we eat? We just couldn't do a good job. Our calorie intake per day would probably exceed our break-even point for maintaining body weight, and we would gain.

So, in order to make sensible choices, it's crucial to know the approximate number of calories in the foods we eat. An easy way to do that is to buy a paperback book in the check-out line of your grocery store that lists the calorie content of usual portions of commonly consumed food and beverages. (Or look them up .) We don't necessarily need to check the list each time we sit down to eat, but knowing typical figures for our favorite foods will enable us to know if we're keeping or exceeding our daily calorie budget.

This is not as awful as it sounds. In fact, there can be pleasant surprises. Suppose I typically get the munchies in the evening, and I roam the house in search of goodies to snack upon. Here is where knowledge of calorie contents can pay off. If I satisfy my munchies by eating cookies, French fries, potato chips or candies, then I'll blow my daily food-budget in just one sitting. But what if I substitute pretzels or unbuttered popcorn? They might be just as satisfying, yet contain fewer calories. So these alternative choices might spare my daily calorie budget at no loss of satisfaction.

As a physician I often encourage my patients to lose weight. Being overweight can increase blood pressure and cholesterol which, in turn, increase the likelihoods of heart attacks and strokes. Heart attacks and strokes are the number one and number three causes of death in the U.S., respectively, and strokes are the number one cause of disability. So we're talking about real conditions that afflict real people. Moreover, our overweight bodies put more stress and strain on our spines and our knees, making them wear out earlier, hurt more, and interfere with quality of life.

Some patients with whom I have this conversation look at me like I'm crazy. They're eating barely enough food to keep a small bird warm, they say. The problem—or the solution—couldn't possibly lie with the food they eat.

The incentives are clear. The choices are ours to make. We shouldn't blame our metabolism. And we shouldn't delude ourselves that we consume barely enough to keep ourselves alive, and yet still, unaccountably, gain weight. We need to take our health into our own hands and start making choices that increase the quality and quantity of our remaining years.

(C) 2005 by Gary Cordingley