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Harvard Commentaries
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Can Nutritional Supplements Enhance Athletic Performance? (Part 1 of 2)

July 09, 2013

By Howard LeWine M.D.

Brigham and Women's Hospital


Performance-enhancing dietary supplements are regularly used by competitive athletes and daily exercisers. Surveys indicate that 75% of college athletes and almost 100% of body builders use at least one product that allegedly boosts performance. Supplemental "ergogenic aids" is the general term for ingested substances that improve efficient use of energy, increase energy production, or shorten recovery time. The growth in the ergogenic supplement industry has been astounding, with new products entering the market weekly. But there is little evidence that the billions of dollars spent on performance enhancers provide the advertised results.

Unlike medications that need to be approved by the U.S. Food and Drug Administration, dietary supplements can be sold without such preapproval. The FDA has used its limited authority to enhance product safety and to pressure manufacturers to accurately label ingredients. The FDA has also been more aggressive stopping promotions and advertisements claiming false benefits. But the agency has a daunting task, because there are so many products, and it has to prove that the products are unsafe or that the promotions are untruthful.

The most popular ingredients in supplements promoted as performance enhancers are vitamins and minerals, amino acids and proteins, and carbohydrates.

Vitamins and Minerals

Although special preparations of high-dose vitamin and mineral supplements are widely advertised as performance enhancing, there is no evidence that mega doses do more than a well-balanced diet. According to the American College of Sports Nutrition, an athlete regularly consuming a diet that provides sufficient protein and calories with plenty of fruits and vegetables should not need extra vitamins and minerals.

Increased demand is made on some of the B vitamins during exercise, including thiamin, niacin, riboflavin, pyridoxine, and pantothenic acid. Enriched cereals and whole-grain carbohydrates combined with some lean meats will satisfy the needs of even the extreme athlete. Vegetarians and other competitors on restricted diets may need some supplementation. Women often need extra iron to replace monthly blood loss from menstruation. A daily generic multiple vitamin with iron is inexpensive and safe insurance if there is any concern that your diet is not providing all that you need.

In general, antioxidants do not enhance performance. The one exception may be vitamin E for high-altitude exercise. One study showed that athletes taking vitamin E at a dose of 400 units per day had more stamina at high elevations compared to those taking a placebo. Most other studies have not shown vitamin E to be superior to placebo at lower altitudes.

Some of the antioxidant vitamins may lessen muscle soreness following exercise by neutralizing free radicals that contribute to exercise-induced muscle damage. The evidence is not conclusive, and the proper doses of vitamins C and E and beta carotene have not been established. Supplemental doses up to 6 milligrams of beta carotene, up to 500 milligrams of vitamin C, and up to 200 units of vitamin E are probably reasonable for this purpose.

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Amino Acids and Proteins

Most amino acids and proteins are not performance enhancing. You do need adequate protein intake to exercise at high-performance levels, but extra protein does not provide a boost. A person who gets little exercise needs only 0.36 grams of protein per pound of body weight daily. Someone exercising vigorously or body building would rarely need more than twice that amount, or about 100 grams of protein per day for a man who weighs 150 pounds.

Whether athletes gain an advantage by eating specific protein sources is being debated. If you decide that you want a portion of your daily protein requirement to be in the form of a protein shake, then a mixture of casein and whey is a reasonable choice. Casein is broken down more and absorbed more slowly, and whey protein results in quicker absorption. But you don't need this on top of your daily protein requirement.

Popular protein supplements often highlight individual amino acids, such as creatine, carnitine, and the branched-chain amino acids (isoleucine, leucine, and valine). Creatine is the one amino acid that may have some athletic benefit. It contributes to rapid energy production and may enhance power or speed bursts requiring short periods of anaerobic activity. It does not build muscle or increase endurance. Creatine can result in water retention. Long-term effects are unknown.

Carnitine, another amino acid, has been hyped based on the hope that ingesting more could increase energy, burn more fat, and produced weight loss. But the carnitine in supplements does not make its way into the body's cells. Extra carnitine just makes you work harder to excrete the extra nitrogen.

The branched-chain amino acids are metabolized by muscle, and this has led to unsubstantiated theories of why they improve performance. In fact, they do not provide additional energy above and beyond other nutrients. Multiple studies have failed to show an exercise benefit.

Too much dietary protein and amino acids can have adverse consequences, such as dehydration, gout, kidney stones, and higher risk of osteoporosis.

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Carbohydrates are the primary fuel for exercise, with oxidation rates reaching 20 times the resting state during peak aerobic activity. Daily exercisers and athletes need to eat an adequate amount of calories to maintain glycogen stores, the sugar banks that can deliver energy rapidly as muscles demand it. Unlike protein, the proper amount of daily carbohydrates is highly variable, depending upon activity level and desire for weight loss vs. weight maintenance. Healthier sources of carbohydrate are whole-grain cereals and breads, fruits, vegetables, and low-fat dairy products. Carbohydrate loading for the seven to 10 days before an endurance event has become less popular. Many athletes do better maintaining their usual diets, making sure that caloric intake is adequate for the upcoming competition.

When exercise lasts more than 60 minutes, a sports drinks or some other carbohydrate source should be consumed to slow down glycogen depletion. Sports drinks provide limited calories, but do enhance water absorption. Bagels, fruit juices, and energy bars are better carbohydrate sources. After exercise, you need to eat some carbohydrates to replenish depleted glycogen stores, especially if you exercise daily or even more frequently.

In Part 2, I will continue my review of nutritional supplements as performance enhancers. You will read about caffeine, DHEA, androstenedione and more.

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Howard LeWine, M.D., is chief editor of Internet publishing, Harvard Health Publications. He is a clinical instructor of medicine at Harvard Medical School and Brigham and Women's Hospital. Dr. LeWine has been a primary care internist and teacher of internal medicine since 1978.

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