Important for all athletes, protein plays a major role in the body such as repair of tissues, production of hormones, growth and fluid balance. According to researcher Carol Byrd-Bredbenner, scientists measure protein quality using various scoring formulas which primarily focus on two things: digestibility and the composition of the amino acids--the individual building blocks of the proteins. Foods can then be compared to a reference protein.

Animal Sources

Bredbenner suggests that animal products contain the highest quality of protein. Egg whites, used as a reference protein, score high in Biological Value, or BV--one scoring method that implies protein absorption and retention. High quality animal proteins with BV scores of 90 or greater (out of 100) include eggs, milk, cheese, poultry, fish, and red meats. Regardless of the source, check for any additional ingredients that tag along with the protein. Researcher Thomas Fahey suggests that red meats have a high protein quality score but can also be high in cholesterol and saturated fats, which can lead to increased cholesterol production in the liver and are associated with risk of heart disease and various cancers. Poultry contains less fat while fish contains good fats called unsaturated fats.

Plant Sources

Besides egg whites, soy scores as highly as animal products in the BV and the Protein Digestability Correction Amino Acid Score--the most widely used scoring formula, according to Bredbenner. However, most plant products have a much lower BV at 70 or lower. Quality plant sources include proteins found in whole grains, nuts, and fruits. In addition to low BVs the Vegetarian Society reports plant foods to be "incomplete" sources because they lack some of the essential amino acids -- those not manufactured by the body. For this reason, vegetarians may require eating several different sources of protein to obtain all the essential proteins necessary for optimal health.

Supplements

One method of obtaining quality protein is through supplementation, either through powders, shakes or solid forms like bars. Ingredients in supplements include caseine and whey--a byproduct of cheese--and individual amino acids such as glutamine. While these products meet the scientific profile for excellent quality, especially whey--which has a BV of 104 and PDCAAS of 1.00--ingesting them in large quantities becomes counter productive. The body can only utilize certain amounts of protein, regardless of the quality, while the remaining amount is converted into energy or broken down and excreted in urine. In relation to excess protein intake, "Today's Dietician" states the strain on the kidneys from the breakdown process can potentially lead to kidney problems as well as dehydration.

 References

• "Food and Nutrition Board, Institute of Medicine, Natinal Academy of Sciences": Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids; 2003
• "Wardlaw's Perspectives in Nutrition"; Carol-Byrd Bredbenner, Gaile Moe; Donna Beshetoor; Jacqueline Berning; 2009
• "The American Journal of Epidemiology": Associations of Dietary Protein with Disease and Mortality in a Prospective Study of Postmenopausal Women; Linda E. Kelemen, Lawernce H. Kushi; David Jacobs; James Cerhan; vol 161; 2005
• "Today's Dietician": Eating A High Protein Diet May Accelerate Kidney Problems; April 26, 2004
• "Fit and Well"; Thomas Fahey, Paul Insel, Walton Roth; 2010
• "The Vegetarian Society" Information Sheet:Proteins; 2010 [http://www.vegsoc.org/info/protein.html]