As you become inundated with ads for new diets, weight loss supplements and muscle-building products, it's easy to get confused. But the best way to make sense of these weight-loss promises and exercise-performance claims is to arm yourself with the facts, says Susan Kalish, executive director of The American Medical Athletic Association.

The association cites several common myths:

Myth: Cutting carbohydrates from your diet is an effective way to lose weight.

"Most individuals on high-protein, low-carbohydrate diets believe they lose weight by eliminating carbohydrates. In truth, they lose weight simply because they have reduced the amount of calories they take in," said Nancy Clark, M.S., R.D., author of "Nancy Clark's Sports Nutrition Guidebook, Second Edition."

"Initially, the weight change is caused by a rapid loss of water, not fat," added Karen Reznik Dolins, M.Ed., R.D., nutrition consultant to the New York Knicks professional basketball team. "And after a short period of time, muscle is lost in addition to fat."

With less muscle, the body burns fewer calories, making this diet a poor choice for long-term weight maintenance.

"Don't be fooled by anyone who tries to convince you that fruits, vegetables and whole grains will make you fat," warned Reznik Dolins. "These foods are an essential part of a healthy diet and, as the primary fuel source for muscles, they are crucial to an athlete's diet."

Without adequate carbohydrate intake, the active person undoubtedly will experience drops in energy levels and exercise performance.

Myth: The fewer calories you eat, the more weight you lose.

This statement is true only to a point.

"If you restrict your calories too much for an extended period of time, you can actually trigger what is known as the 'starvation adaptation response,'" explained Dr. Susan M. Kleiner, author of "High Performance Nutrition." "This simply means that your metabolism slows down to accommodate your lower caloric intake, and your body conserves fat rather than burning it for energy."

Even a person who works out regularly can hold onto body fat and end up at a weight-loss plateau if not enough calories are being consumed.

"Low-calorie diets are also a disaster for anyone wanting to maintain or build muscle. Such diets cause your body to store fat, as well as burn healthy muscle," Kleiner warned. "Never go below 1,200 calories per day if you're a woman and 1,600 if you're a man."

Myth: To build muscle, you need to supplement your diet with extra protein.

"There is no research showing that taking in extra protein enhances muscle weight gain," said Dr. Melvin Williams, author of "The Ergogenics Edge."

Active individuals need about 12 percent or 15 percent of their total daily calories to come from protein. Some may need more than the Recommended Daily Allowance (RDA) of 0.8 grams of protein per kilogram of body weight, but even they should not exceed a level of two to 2.5 times over the RDA.

"For an endurance athlete, the upper level of the recommended amount is 1.4 grams per kilogram body weight; for a strength-trained athlete, the upper level is 1.8 grams per kilogram of body weight," said Williams.

Excess protein in your diet can cause dehydration, kidney and liver problems and, according to a study by the National Cancer Institute, it has been linked to kidney cancer.

Myth: The less body fat you have, the better.

Female athletes who lose too much body fat can be at risk for a condition referred to as The Female Athlete Triad. This condition is characterized by inadequate nutrition, loss of menstruation and early-onset osteoporosis, which often is irreversible. In women, fat is needed to support child-bearing functions and essential fat (11 percent to 13 percent for women and 3 percent to 5 percent for men) provides calories for energy, protects internal organs, makes hormones and keeps you warm.

"For optimal health, no one should drop below their level of essential fat, nor should they exceed ranges that would put them at risk for heart disease, diabetes, high blood pressure and stroke," advised Kalish.

Women should not exceed 27 percent body fat; for men, that figure is 17 percent, according to Clark.

Myth: Sweating is a great way to lose weight.

"Sweating is the way your body cools itself, and weight loss during exercise often represents a loss of fluids from the body -- not a reduction of fat," said Kalish. "Rather than rejoicing about the number of pounds you've lost, you should calculate the amount of fluids you need to replace. For every pound you lose following a bout of exercise, you should drink at least 24 ounces of fluid."

Progressive dehydration occurs if you do not fully rehydrate after each workout, and this can have a negative effect on your health and exercise performance.

Source: The American Medical Athletic Association, 4405 East West Highway, Suite 405, Bethesda, MD 20814.