If you think sit-ups will make you lose weight around your middle, you have fallen prey to one of many myths about exercise, says Dr. Charlie Kuntzleman, a physical fitness consultant who spoke in honor of National Nutrition Month at the Department of Health and Human Services last week.

Spot reducing is impossible, says Kuntzleman. Exercise can tone specific areas -- upper arms, stomach, things -- but weight loss comes equally from fat cells all over the body.

Decked in sauna suits, some people run or bike in the heat of the day hoping to drop pounds of sweat. "You can't sweat pounds off," says Kuntzleman, meaning that you might lose water but you won't lose a greater number of calories.

Kuntzleman points out the irony of exercise machines in American society. We got fat because machines began to do most of our work. Now we depend on the third myth, "that exercise machines help you lose weight," For the most part, that's false, says Kuntzleman, who advocates only the stationary bicycle and treadmill as effective exercise machines.

And exercise does not increase your appetite, he said, contradicting the last of the famous myths. In fact, increased exercise can diminish appetite.

This becomes more important as we grow older because with each decade after age 26, our metabolic rate slows 2 percent. That means you don't burn calories as efficiently, so that you begin to gain weight even though your eating patterns haven't changed at all. With age, heart rate increases, blood pressure increases, muscle elasticity decreases and so does the ability to take in and use oxygen.

Exercise can arrest those symptoms of aging, according to Dr. Gabe Mirkin, running columnist and Maryland physician. Exercise also increases the muscle tissue, and the more muscle tissue you have, the more calories you burn while resting.

Clearly, says Kuntzleman, there's more to maintaining and losing weight than calories. He recommends that people fight a sedentary existence by walking, running, bicycling, swimming or cross-country skiing.

Physical fitness complements a life style that also includes a variety of foods eaten in moderation as close to their natural state as possible. Stuffed winter squash fits into such a life style, especially when you'd rather spend your time running than cooking.

EXPRESS LANE LIST: lamb, rice, tomato paste, scallions, cumin, butternut or acorn squash, cucumbers and yogurt. STUFFED WINTER SQUASH (4 servings) 2 acorn or butternut squash 1/2 pound ground lamb 2 tablespoons tomato paste 2 tablespons tomato paste 3 tablespoons chopped scallions 1 teaspoon ground cumin 1/2 teaspoon salt 1/2 teaspoon freshly ground pepper

Halve squash. Slice the stem of the squash and scoop out the seeds Cut a thin slice from the underside so the squash halves, cavity side up will lie flat and steady in a baking dish. Cover tightly and bake about 30 minutes at 350 while you prepart the meat. Cook the lamb in a medium skillet and drain excess fat. Combine lamb with rice, tomato paste-scallions, cumin, salt and pepper Scoop mixture into squash shells cover tightly, and cook about 30 minutes more. Serve with a salad made by slicing 2 cucumbers and combining them with 1 container (8 ounces) plain yogurt and 3 tablespoons minced scallions. Total calories per meal (1/4 of the salad and I filled squash half): about 515.