Protein molecules are composed of sub-units called amino acids. Twenty different amino acids are found in proteins in the body. Nine are essential amino acids, which means they must be derived from food, and the remaining 11 are nonessential, as the body can manufacture them if necessary. According to "Advanced Fitness Assessment and Exercise Prescription," a healthy individual who maintains a well-balanced diet does not require amino acid supplements; ingesting large quantities of amino acids can pose serious health risks.
The fate of an amino acid after it is transported to the liver is highly dependent upon the body's needs at that moment. The recommended protein intake for an average individual is 0.8 g per pound of body weight per day. Any amino acids not used within a short time cannot be stored for future use, but will be converted to glucose and burned as energy or converted to fat or glycogen for storage. Since the average American diet exceeds the daily protein requirements, unnecessary amino acid supplementation can lead to weight gain.
Dangers for Athletes
According to "Advanced Fitness Assessment and Exercise Prescription," endurance athletes require 1.2 to 1.4 grams of protein per pound of body weight per day; strength-training athletes need 1.6 to 1.8 grams. These requirements are easily met through diet. Amino acid supplementation can work against an athlete by increasing the risk of dehydration, as extra water is required to rid the body of the byproducts of protein metabolism. Also, amino acid supplementation makes it difficult for an athlete to incorporate enough carbohydrates to ensure adequate stores of glycogen in the muscles.
Amino Acid Imbalances
Taking single-amino-acid supplements can cause imbalances that may interfere with normal absorption of food-derived amino acids. Certain groups of amino acids compete for carriers to transport them across the intestinal wall for entry into the blood stream. When an amino-acid supplement is ingested, it floods the transport carriers with that particular amino acid, which may result in other amino acids not being absorbed in proper amounts.
Processing excess protein can overburden disease-damaged livers and kidneys. Individuals with kidney or liver disease are often placed on a protein-restricted diet. Eating a life-long high-protein diet may be responsible for the slight decline in kidney function that usually occurs with age, according to "Total Nutrition: The Only Guide You'll Ever Need." However, this connection is still under investigation.
Adding purified protein supplements and amino-acid mixtures that have had their phosphate removed may increase the excretion of calcium by the kidneys. A study published in the "American Journal of Clinical Nutrition" found that excess protein intake is a significant risk factor for calcium loss. Ingesting excessive amounts of protein over a prolonged period of time reduces calcium absorption and can lead to bone resorption, resulting in osteoporosis.
- "Advanced Fitness Assessment and Exercise Prescription"; Vivian H. Heyward, Ph. D.; 2006
- "Total Nutrition: The Only Guide You'll Ever Need"; Victor Herbert, Genell J. Subak-Sharpe; 1995
- "American Journal of Clinical Nutrition"; Dietary Protein Intake and Urinary Excretion of Calcium; Roichi Itoh et al.; August 1998