Editor’s Note: This is the second of four articles looking at how dietary supplements affect athletic performance.
Last week, I discussed the ergogenic qualities of vitamins and minerals. This week, I focus on amino acids and proteins. In general, compounds from these categories are relatively safe when taken in the prescribed dosages. Some of them do indeed improve performance if an athlete is not getting sufficient amounts from a balanced diet.
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 bodybuilding 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 produce 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.
Next week: How caffeine can boost athletic performance.
Dr. Howard LeWine is a member of the Harvard Medical School faculty and practicing internist with Harvard Vanguard Medical Associates and Brigham and Women’s Hospital, Boston. He serves as chief medical editor of Internet Publishing at Harvard Health Publications.
