Edition: U.S. / Global

Fitness; It May Not Be Exciting, But You'll Perform Best With a Balanced Diet

By William Stockton
Published: January 25, 1988

ONE of the enduring myths of athletics is that eating protein will enhance one's performance. Since protein is composed of amino acids, some advocates take the notion one step further: loading up on certain amino acids will improve strength, promote muscle building and increase performance.

But a growing body of research has found no evidence that increasing protein intake - and particularly consuming specific amino acids through supplements - has any relation to fitness.

''Excessive protein consumption has not been demonstrated to enhance athletic performance,'' the American Dietetic Association said in a paper on nutrition for fitness published last year. For high performance athletes, ''there is no evidence that very-high-protein diets commonly consumed by these athletes will help to increase muscle strength or protein content'' of the body, the paper said.

How much protein we should eat each day has generated great amount of controversy. Sports doctors and nutritionists offer advice that sounds too boring and pat in this high-tech age: eat a normal, well-balanced diet.

The recommended dietary allowance (RDA) of protein for an adult is eight-tenths of a gram for each kilogram of body weight. Thus, a man who weighs 180 pounds, or 82 kilograms, would need about 66 grams of protein, or about two ounces, each day.

But studies of young athletes exercising strenuously have suggested that in such situations protein in the muscles is broken down and converted into energy. Such results have been enough to send anyone trying to build up muscle diving for a juicy steak and a sack of soybeans.

In its paper last year, the dietary association conceded that the protein RDA might be too low for someone who is highly active. It cited a recent study that suggested that 1 gram of protein per kilogram of body weight might be necessary. Thus, the 180-pound man would need 82 grams of protein each day, instead of 66.

But consider how little protein that is: A typical hamburger with a quarter pound of meat and a slice of cheese has about 40 grams of protein. Two eggs, two cups of milk and four tablespoons of peanuts would provide another 40 grams. Even pasta, that wonderful mother lode of carbohydrates, has 5 grams of protein per cup.

Studies of dietary preferences have found that Americans consume twice as much protein as they need, whether they are athletically active or not. Most people, even those athletes who make supreme demands on their bodies, are in little danger of not getting enough protein.

Moreover, in the past, it was thought that while eating extra protein did not accomplish anything, neither was it particularly harmful. Medical orthodoxy said that the body took the amino acids it needed from the protein we ate to build new protein and converted the excess to energy. The amino acid supplements were simply excreted.

But there is growing evidence that eating too much protein or taking amino acid supplements can be harmful. Experts in kidney disease and digestive processes say that it can cause subtle but long-term damage to the kidneys and interfere with the normal digestion of protein.

The kidney connection is the most ominous. Concern about it grows from increasingly sophisticated knowledge of how the kidneys work and how their performance can be substantially diminished, particularly later in life.

''It's a strong line of thinking among many of us and there is some convincing evidence, but not everyone agrees yet,'' said Dr. Sheldon Glabman, clinical associate professor of medicine at the Mount Sinai Medical Center in New York and a kidney disease specialist.

One of the kidneys' essential roles is handling the nitrogen-containing waste products produced as the body metabolizes the amino acids consumed from proteins in the diet. When we are born, our kidneys have an enormous reserve of the cells that handle protein wastes. As we age, some of these cells fail, but reserve cells take over.

Citing evidence from the study of laboratory animals as well as patients, many kidney specialists now believe that a lifetime of eating more protein than the body needs puts demands on the kidney cells held in reserve, steadily diminishing the organ's capacity. Should someone of advancing age encounter a medical emergency that severely tests the kidneys, they could fail.

Amino acid supplements carry with them another hazard: alteration of digestive processes.

When we eat protein, the digestive system breaks it into the separate amino acids, or sometimes molecules of a few amino acids linked together. They are then absorbed into the blood at receptor sites in the small intestine. Different receptors have different roles. Some may absorb only a particular amino acid, while others can absorb several.

If an amino acid supplement is taken in the mistaken belief that it will enhance athletic performance, it passes into the intestine and floods the receptors intended to handle it. If those receptors also handle a few other amnio acids, the other amino acids are likely to be crowded out and excreted from the body without being taken into the blood.

Although recent research supports this idea, evidence is lacking as to how long such alteration of protein digestive processes might last and whether blockage of the uptake of some amino acids could cause an amino acid deficiency.