You've seen the ads in health magazines—the ones proclaiming that you can't get enough essential amino acids in your diet, that you need polar bear-size portions of meats and fish to get the protein you need to replenish your body after exercise. You may even have heard terms like arginine and leucine being bandied about the gym by the buff set.

Should we all be supplementing our diet with amino acid pills, powders, and potions? Not according to Jackie Berning, R.D., a professor and registered dietitian at the University of Colorado, who believes that people are pissing away their money—literally. "Most persons taking these aminos have the most expensive urine in town." Added protein, she says, can put undue strain on the kidneys, liver, and heart to process it through the digestive system. Charles Mueller, M.S., R.D., nutrition manager in the clinical research center at New York Presbyterian Hospital, agrees. "Most Americans get four times as much protein as they need. It's why the U.S. has the highest rates of kidney failure."

Then there's the matter of the cost. Most supplements, explains nutritionist Leslie Bonci, M.P.H., R.D., contain between 500 to 1,000 milligrams of amino acids per dose, whereas an egg or slice of turkey breast contains 7,000 milligrams for a fraction of the price. "Supplements also do not contain the vitamins, minerals, and other nutrients found in protein-containing foods," says Bonci.

Some nutritionists feel that protein supplementation is more of a practical issue because of its convenience and pure form. "There are times, particularly following exercise, when having a very high-quality protein that is easily digested and contains no fat or lactose, is desirable," says Susan Kleiner, Ph.D., R.D., author of Power Eating and Power Eating and Fitness Log. "The availability of all the essential and nonessential amino acids at this time will enhance muscle building and recovery."

No one questions the body's need for amino acids. Aside from fighting disease and repairing tissue, these "building blocks" constitute protein itself in various combinations. With a normal diet, the body produces 13 of the 22 amino acids that are categorized as essential; the other nine must come from outside sources, such as specific foods.

How much protein do you need? The Recommended Dietary Allowance is 0.4 g per pound of body weight for a sedentary adult. Nutritional experts agree, though, that our protein needs must increase with exercise—from 0.5 to 0.75 grams for an adult who's exercising three times a week to 0.6 to 0.9 grams for an athlete. For a 175-pound, moderately active man, that translates to about 88 to 131 grams per day. According to the most recent government statistics, the average American man between the ages of 20 and 59 gets about 105 grams of protein a day; females in the same age range average 69 grams. (To put this into perspective, one large egg contains 6 grams of protein, and a 4-ounce chicken breast has 35 grams.)

Berning believes that even bodybuilders can get enough aminos from eating a normal diet of mostly carbohydrates, some protein, and a little fat. In fact, she cites recent studies that a high-carb diet actually grows more muscles than a protein-based one. "The best thing to do is eat a balanced diet," Mueller agrees. "And eat enough of everything."

It is also not necessary to consume protein from animal sources. Combining grains and beans (including peanuts)—especially if dairy products are thrown into the mix—will result in the same ratios of essential amino acids as chicken, fish, eggs, or beef. Eggs, however, provide the highest-quality protein of all. "All protein is measured against the egg," Mueller points out. "Egg whites have all the essential amino acids."

The bottom line on the amino acid debate? Before you sip that protein-powered shake or pop one of those pills, first consider whether you really need it.