For the average person looking to lose or maintain a healthy weight, experts at the Duke Diet & Fitness Center recommend what most of us already know, but few of us put into practice: regular exercise combined with a balanced, reduced-calorie diet low in saturated fat and high in vegetables, fruits, and whole grains.

Why low fat and not low carb? "If you eat a low-fat diet conducive to weight loss, you're going to see metabolic improvements," explains Elisabetta Politi, nutrition manager for the Duke Diet & Fitness Center. "Your cholesterol, blood sugar, and blood pressure will all go down."

Politi discourages clients who are not overweight, particularly those who exercise strenuously, from experimenting with low-carb diets, noting that for those individuals "it's not a healthy way to go. Carbohydrates are the fuel that helps run your body more efficiently."

"I think it's okay to eat lean protein and heart-healthy fats instead of refined, processed carbohydrates," she adds. "But I still would recommend eating at least a serving of grain per meal, which is less than half of what the food pyramid recommends."

If you're significantly overweight and if a low-fat diet hasn't worked for you, Politi says that's when it might make sense to try a low-carb diet.

Politi's clients do it under medical supervision. The first two weeks they may start with a very low-carb regimen of 20 to 35 grams of carbs per day, or about 12 percent of their calories from carbs. But they quickly move to a moderate low-carb diet, with about 35 percent of their calories from carbs--two servings of starches or grains a day, one at breakfast and one at lunch. For dinner, they eat lots of heart-healthy oils and protein--fish, chicken, and meat--with lots of vegetables.

"I tell clients that, when they go home, they should be eating several servings of grains a day," Politi says, and that they should combine this with a regular program of aerobic and strength exercise. "Studies have shown that a combination of strength exercises and cardio is the most beneficial for weight loss. You need the strength component because with any weight-loss program you're going to lose a little muscle and with strength training, you're going to build muscle. We recommend that, when they go home, they exercise an hour a day, five to six times a week, if they want to be successful at weight maintenance."

Despite the "No pain, no gain" attitude of hard-core exercisers, Howard Eisenson, director of the Duke Diet & Fitness Center, says there's no need to huff and puff through each cardio workout. Keep it moderate, at an intensity that allows you to carry on a conversation. "Moderate intensity exercise is probably sufficient for weight-loss purposes," he says. "If people are trying to optimize their cardiovascular fitness, there may be an advantage to having at least part of their exercise toward the higher intensity activities, working at 60 to 80 percent of their maximum."

In any case, shoot for an hour a day of aerobic exercise on most days of the week, as recommended by the Institute of Medicine, Eisenson says, and don't ignore strength training, which should be incorporated two to three days a week, along with flexibility and balance exercises. Also, don't forget that each of these weight workouts should be separated by at least forty-eight hours to allow the muscles to rebuild and repair themselves.

Strength training is more important than many of us realize in helping us stay trim as we age. Wayne Westcott, a national fitness authority who serves as the fitness research director at the South Shore YMCA near Boston, says that without any form of strength training, our bodies will lose about one pound of muscle every two years. That means a forty-year-old woman who weighs the same as she did in college has replaced 10 pounds of muscle with 10 pounds of fat, even though she may weigh the same.

This gradual loss of muscle mass is the primary reason that it gets harder to lose or maintain weight as we age. Every pound of muscle we lose lowers our metabolic rate by 50 calories a day and every pound of muscle we gain raises it by 50 calories a day, Wescott says, so that the typical individual who does no strength training for ten years and has lost five pounds of muscle, must eat 250 fewer calories a day just to keep from gaining weight. Far better to feel the burn two days a week, than to go cold turkey on apple pie.

If you're like most people and are having trouble maintaining an exercise routine once you start, fitness professionals recommend three keys to keeping an exercise program going: find an activity you enjoy; find someone or a group of individuals with whom you enjoy doing that activity; and make it a routine part of your daily schedule.

If you can fit your workouts in the early morning hours, before work and family responsibilities put the squeeze on your time, that usually works best, since it prevents the inevitable crisis at work or at home from derailing your bike, run, or swim for the day. But if you're not a morning person or need to send the kids off to school, pick another time, like the noon hour, that you can call your own.

And one last thing, the experts say: Before beginning an exercise program, check with your doctor if you're over forty or have cardiovascular risk factors, such as a history of smoking, high blood pressure, high cholesterol, diabetes, or a history of heart disease in your family.

-- Kim McDonald