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PROTEIN

Since ancient times, athletes have eaten specific animal parts to try to improve agility, speed and strength. In 1842 John Von Liebig stated that the primary fuel for muscular contraction was protein. However, this belief was disproved in the late 1800s.

What is Protein?

Protein is an essential nutrient composed of carbon, nitrogen, hydrogen, oxygen, and sometimes sulfur. It is necessary for a variety of functions in the body. The three main functions of protein include:

1. Growth, development, and repair of muscle tissues
2. Regulation of metabolism through reactions controlled by enzymes
3. An energy source when calories from fat or carbohydrate are deficient

Once protein enters the body it is broken down into amino acids, these are the building blocks of protein. There are twenty amino acids, of which nine are essential amino acids and the rest are non-essential. The non-essential amino acids are produced by the body, and the essential amino acids are not, therefore, they must be consumed in the diet. The essential amino acids include: leucine, isoleucine, lysine, methionine, threonine, phenylalanine, tryptophane, valine, and histidine. In order for protein to function properly in the body, the following three conditions must be met in the diet, 1) enough essential amino acids to meet requirements; 2) an adequate amount of non-essential amino acids; 3) and an adequate amount of calories.

Where is protein found and is there a difference in quality?

There are two main sources of protein, plants and animals. These sources differ in the quality of protein they provide. In general, high biological proteins (complete proteins that contain all of the essential amino acids) come from animal sources, such as meat, fish, poultry, and eggs, (these proteins may also be referred to as complete proteins). In contrast, plant sources of protein, legumes, nuts, seeds, cereals, and vegetables are lower in biological value because they do not contain all of the essential amino acids. For example, plant foods are lower in lysine than animal foods. Although a plant protein does not contain all the essential amino acids, plant proteins are often higher than animal proteins in sulfur-containing amino acids.

Are animal sources of protein better, since they are of higher biological value? The answer is, "not necessarily." Animal protein sources tend to be higher in fat and lower in fiber than plant protein sources. High protein intakes from animal sources have been associated with increased risk of heart disease, chronic disorders, and some cancers. For this reason, plant sources of protein may be preferable to animal sources, if a variety of plants are used. Animal protein does not need to be avoided as it is still a good source of nutrients, but lower-fat items such as poultry and fish and limited portion sizes of higher-fat meats are desirable. A variety of proteins from plants and animal sources should be consumed, to assure that the diet has an adequate amount of protein, with a balance of amino acids.

What is the recommended intake of protein?

The Recommended Dietary Allowance (RDA) for protein is .33 gram (g) of protein per pound of body weight per day. This means that for a 150 lb female, 50 g (150 lbs x .33 g protein) of protein should be consumed in the diet daily. This translates to approximately 12-15% of the total daily calories from protein. This recommendation is for the healthy, moderately active adult. The amount of protein increases slightly for those people that are more active, due to increased needs to build and repair muscle.

Does an athlete need more protein?

This is an important question regarding protein needs that must be carefully phrased. If the question reads, "Does exercise increase protein needs above what we currently consume?" then the response will be different from the answer to this question: "Does exercise increase protein needs above the RDA of 0.33 g/lb body weight?" The answer to the second question is yes. Physical activity does seem to increase protein needs above the RDA for both endurance and strength-training activities, due to an increase in the utilization of several amino acids, especially branched chain amino acids (leucine, isoleucine, and valine). The increased utilization of protein can account for up to 10% of energy production during endurance exercise.

For athletes in training, the recommended protein intake is .5-.9 g/lb body weight. For example, a 150-lb athlete should consume 75-135 g of protein (0.5-0.9 g/lb body weight x 150 lb= 75-135 g of protein). A diet providing 12-15% of its calories from protein should meet this requirement if you are consuming enough calories to meet your energy needs. Protein intake in excess of these requirements is usually not necessary and does not seem to have any benefits for either strength or endurance training.

There is a limited amount of research done on women and their protein requirements. The above recommendations for protein are based primarily on research done on males. Protein requirements may be different for male and female athletes. In fact, preliminary studies have demonstrated that males may have a higher protein requirement than females.

In addition to protein, what other nutrients do I need to build muscle?

The previous suggested levels of protein are adequate when caloric intake is sufficient; however, if insufficient, then a higher proportion of protein to calories must be consumed to meet protein needs. A vegan athlete may also have increased protein needs, since plant proteins are of a lower biological value, but a mixture of plant proteins can be equivalent to animal proteins. Vegetarian diets also tend to be more filling, which may make it harder for an athlete to consume adequate calories and protein. To help avoid an inadequate protein consumption, the vegetarian athlete should consume a variety of plant foods and include tofu or other soy-based products.

The requirements for protein may be further increased for athletes starting or increasing training. Athletes in early stages of training may require up to 1.0 g of protein per pound of body weight to meet the increased synthesis of enzymes, myoglobin (oxygen-carrying protein specific to muscle only), hemoglobin, and the increased number of mitochondria that develop during the early training periods. This amount equates to 150 g protein per day for a 150 pound athlete. This quantity is obtainable in 10 ounces of meat, chicken, fish, or cheese; 3 cups low-fat or skim milk; 2 cups vegetables; and 15 servings of bread or starchy foods (including pasta, rice, cereals, and bread).

A study looking at the effects of diet on muscle and strength gains during resistance training indicated that a high calorie diet consisting of, 65% of total calories from carbohydrates increased more lean body mass than a high calorie diet consisting of 40% of the total daily calories from carbohydrates. Thus, although protein may be a focus for many athletes, consuming adequate carbohydrate is also important.

Carbohydrate consumption is also important immediately following resistance training. Studies have shown that consuming 1 g of carbohydrate per kg of body weight, within one hour after resistance training can decrease protein breakdown. This leads to a positive protein balance, which is needed to promote muscle growth.

Muscle contains approximately 22% protein, 72% water, and 6% fat. To add 1 pound of muscle per week, an additional 100 grams of protein per week is needed in the diet. This is only 14 grams of protein per day, which is obtainable in 2 oz meat, chicken, fish, or cheese or 2 cups low-fat or skim milk. Extra protein is not preferentially laid down as muscle mass. Instead, extra protein will be:

• used as an energy source if calories or carbohydrates are inadequate
• stored as fat if protein is in excess of caloric needs, or
• used for its primary and structural roles (formation of tissues, hormone and antibody formation, maintenance of water and acid-base balance, and control of blood-clotting processes).

Can excess protein intake be harmful?

Protein metabolism releases nitrogen in amino acids as a by-product. This nitrogen must then be eliminated from the body through the kidneys. Water is needed to help excrete nitrogen. Therefore, an excess of protein can result in water loss, frequent urination, and dehydration, all of which can lead to a decrease in performance. This process also places excess stress on the liver and kidneys.

Are supplements good sources of protein?

Protein supplements are an expensive way to get protein into your diet. They contain about 16 to 55 grams of protein and cost around $20.00 to $60.00. A can of tuna costs around $1.00 and provides about 37 grams of protein. Most people can easily get the protein they need from their diet. Vegetarian athletes, or those who consume very low calorie diets may not get the protein they need every day. These athletes may choose to take a protein supplement and should choose one that contains all nine essential amino acids.

The Bottom Line

• Adequate protein intake is essential for top performance.
• The recommended protein intake for an adult competitive athlete is .5-.9 g pro/lb body weight along with adequate energy intake. If calorie intake is insufficient, a higher proportion of protein to calories must be consumed to meet protein needs.
• Protein needs can easily be met by a well balanced diet following the Food Guide Pyramid guidelines, and protein supplements are simply an expensive way to get protein into your diet.
• A high protein diet for weight loss or enhanced performance is not recommended, and may have adverse effects.

References

1. A Day in The Zone. Tufts University Diet and Nutrition Letter, May 1996, pg 5.
2. Alberts, N. Up with protein, down with carbs? Self, March 1997. pgs 131-133, 169.
3. Atkins, R.C. Dr. Atkins' New Diet Revolution. New York, NY; Avon Books, 1997.
4. Bucci, L. Nutrition and Ergogenic Aids for Sports and Exercise. Boca Raton, FL: CRC Press, pgs 13-18, 1994.
5. Clark, N., and C. Rosenbloom. To zone or not to zone: People respond to the zone diet plan. SCAN's Pulse, 5-7, 1997.
6. Coleman, E.J. The biozone nutrition system: A dietary panacea? International Journal of Sports Nutrition 6:69- 71, 1996.
7. Dohm G.L. Protein as a fuel for endurance exercise. Exercise and Sports Science Review. 1986;14.
8. Eades, M.R., and M.D. Eades. Protein Power. New York, NY: Bantam Books, 1996.
9. Entering a high-protein twilight zone. Tufts University Diet and Nutrition Letter, May 1996, pgs 4-6.
10. Evans W.J, E.C.Fisher, R.A. Hoerr, V.R. Young. Protein metabolism and endurance exercise. Physician and Sports Medicine. July 1983;11:7.
11. Goodman M.N. Amino acid and protein metabolism. In: Exercise, Nutrition and Energy Metabolism. New York, NY: Macmillan Publishing Co: 1988.
12. Haymes E.M. Proteins, vitamins, and iron. In: Ergogenic Aids in Sports. Champaign, IL: Human Kinetics Publishers; 1983.
13. Heller, R.F. and R.F. Heller. Healthy For Life. New York, NY: Penguin Books, 1995.
14. Lemon P.W.R, and M.M. Chaney. The role of protein in physical activity. In: Report of the Ross Symposium on Muscle Development: Nutritional Alternatives to Anabolic Steroids. Columbus, Ohio: Ross Laboratories, 1988.
15. Leibman, B. Carbo-Phobia: Zoning out the new diet books. Nutrition Action Healthletter, July/August 1996, pgs. 3-5.
16. Meredith C.N. Protein needs and protein supplements in strength-trained men. In: Report of the Ross Symposium on Muscle Development: Nutritional Alternatives to Anabolic Steroids. Columbus, Ohio: Ross Laboratories, 1988.
17. Puhn A. The 5-Day Miracle Diet. New York, NY: Ballantine Books, 1996.
18. Ruud, J.S. Nutrition and the Female Athlete. Boca Raton: CRC Press 1996, pgs 38-42.
19. Ryan M., and J. Ellis. Reviews. SCAN's Pulse. Spring 1997, pg. 17.
20. Sears, B., and B. Lawren. Entering the Zone. New York, NY: Harper Collins Publishing, 1995.
21. Should you be eating more protein, or less? University of California Berkeley Wellness Letter. June 1996, pgs. 4-5.
22. Submitted for your approval: Should you enter the zone? Environmental Nutrition, January 1996.
23. Taking Aim at the Zone. Penn State Sports Medicine Newsletter. 5(8):1-2, 1997.
24. Williams M.H. The role of protein in physical activity. In: Nutritional Aspects of Human Physical and Athletic Performance. Springfield, IL: Charles Thomas Publishers, 1985.

UNIVERSITY OF ARIZONA; HEPTATHLETE DEVELOPMENT PROJECT 

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