What is protein?
What is the structure of protein?
What are some of the issues related to protein supplements?
What are protein requirements?
What are the possible adverse effects of using protein supplements?
What are some common sources of protein and amino acid products?
What are the effects/actions of L-Carnitine?
What are the adverse effects of using L-carnitine supplements?
Does carbohydrate supplementation during exercise improve performance?

• What is the structure of protein?
  Protein is a complex chemical structure containing carbon, hydrogen and oxygen similar to carbohydrates and fat. Protein also has nitrogen. These elements are combined and are formed into amino acids, each possessing an amino group (NH2) and acid group (COOH), and the reminder being different combinations of carbon, hydrogen, oxygen and sometimes sulfur. There are 20 amino acid (peptides), all of which can be combined together in different ways to form proteins that are needed for the structure and functions of the human body (Williams, 1893).

• What are some of the issues related to protein supplements?

  1. Athletes may use protein supplements to enhance endurance and increase or maintain muscle mass to improve strength and size.
  2. A high-protein diet doesn't build muscle and burn fat as some people think.
  3. Regular physical activity and dietary protein builds muscle strength.
  4. Athletes may need slightly higher levels of protein, derived from protein-rich foods such as meat, poultry, fish, eggs, and dairy products.
  5. Depending on the protein sources chosen, a high protein diet may also be high in fat and calories.
  6. Diets very high in protein can put a strain on the liver and kidneys.

  (From The American Dietetic Association's Complete Food & Nutrition Guide, 1998)

• What are protein requirements?

  1. The RDA for protein is 0.8 grams/kg/day.
  2. Adequate energy intake primarily from carbohydrates will insure protein balance.
  3. Urea, a by product of protein metabolism, increases in the urine during exercise.
  4. Estimates of increased protein requirements for endurance athletes vary, with recommended protein intakes of 0.97 to 1.39 g/kg/day.
  5. Most experts agree that additional protein can be easily obtained through a balanced diet.
  6. Protein need can be calculated as a percentage of total energy and on a per kilogram body weight basis (American Dietetic Association, 1997).

   
• What are the possible adverse effects of using protein supplements?

  1. High protein diets are discouraged by most nutrition experts due to increased stress placed on the kidneys.
  2. The high nitrogen load excreted as urea can cause fluid imbalance leading to dehydration.
  3. Diets high in animal sources of protein are often associated with high fat intake and increased risk of heart disease.
  4. Large ingestion of some amino acids can interfere with the absorption of other amino acids leading to metabolic imbalances.
  5. Mild to severe stomach cramping and diarrhea, dehydration, and gout have been associated with use of certain amino acid supplements.

   
• What are common sources of protein and amino acid products?

  1. The protein content of powdered or liquid protein formulas is derived form natural food sources such as milk, egg, or soy protein.
  2. Amino acids marketed as ergogenic aids include the branched chain amino acids (BCAA) leucine, isoleucine, and valine. During exercise the liver releases BCAA which are delivered to the muscle. Degradation of muscle protein which also occurs during exercise leads to the production of BCAA within the muscle.
  3. Leucine is the only amino acid that can be oxidized for energy and is important in muscle metabolism because it can provide energy to muscle during starvation. Leucine also has a stimulatory effect on the secretion of insulin.
  4. Over secretion of insulin can result in a decrease blood sugar and reduced athletic performance.

   

• What are the effects/actions of l-carnitine? Carnitine (L-3 hydroxytrimethylammoniobutanoate) has several roles on the mammalian cellular metabolism. L-carnitine is believed to increase long chain fatty acid oxidation in skeletal muscle during exercise. Dietary sources of carnitine are meat and diary products. Advocates of L-carnitine supplementation claim that it increases aerobic and anaerobic capacity and promotes fat loss. The most commonly cited dosage of oral carnitine is 2-6 g/day consumed in two to three doses with meals. L-carnitine supplementation may have beneficial properties, however, there is a lack of information regarding its long term use (Tonda and Hart, 1992).

• What are the adverse effects of using l-carnitine supplements?
  Nausea, vomiting, abdominal cramps, diarrhea

• Does carbohydrate supplementation during exercise improve performance?
  Research has shown that carbohydrate supplementation during exercise can improve long-term endurance performance (for activities lasting 90 minutes or more) and delay fatigue 30 to 60 minutes. The most recent guidelines on carbohydrate supplementation during exercise are the following recommendations:

  1. Consume 200-400 ml of a moderately concentrated 5-7% carbohydrate drink.
  2. Continue consuming 100-150 ml of the same drink at 10-15 min intervals for the first two hours of exercise.
  3. After two hours switch to a more concentrated drink (15-20% carbohydrate).
  4. Choose a drink that is palatable.
  5. One alternative to purchasing sports drinks is to dilute any fruit juice 1:1 with water and add a teaspoon of salt per liter. This should approximate carbohydrate, electrolyte and osmolality values of commercial sports drinks (Wolinsky, 1997).

Continue on to: Vitamins and Minerals

Back to the top of Protein and Amino Acid Supplements
Back to Nutritional Supplements.
Back to Choices in Sports.
Feedback and Comments.