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Complete protein, also known as whole protein, contains all nine essential amino acids necessary for the dietary needs of humans in the correct proportion. Incomplete proteins may either lack in some amino acid, or contain all essential amino acids, but not in correct proportions to support the biological functions of the human body. A healthy diet requires selection good sources of complete protein.
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Almost all whole foods contain protein, but not all such food sources provide complete proteins. The U.S. Food and Drug Administration in collaboration with the World Health Organization promotes the protein digestibility corrected amino acid score (PDCAAS) as a method to evaluate the protein quality of food. This method considers the amino acid requirements of humans and their ability to digest it, and ranks foods that fulfill such needs on a scale of 0 to 1
The PDCAAS method compares the amino acid profile of the food against the standard amino acid profile, using the formula = (milligram of limiting amino acid in 1 gram of test protein / milligram of same amino acid in 1 gram of reference protein) x fecal true digestibility percentage.
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The highest protein content food need not always be the best choice for complete proteins. The best food sources of complete proteins are animal foods such as meats, fish, poultry, seafood and diary products such as cheese, eggs, yogurt and milk. The only non-complete animal food is gelatin.
Proteins from plant foods such as legumes, grains, beans, and vegetables contain incomplete protein, lacking in amino acids such as in lysine and tryptophan. Two note-worthy exceptions are soybeans and quinoa.
Whey, egg white, and soy protein isolates are the highest complete protein foods, all with PDCASS scores of 1.0. Beef has a PDACSS score of 0.92, and soybeans 0.91. Chickpeas has a score of 0.78, most fruits score 0.76, and most vegetables score 0.73. Foods especially low in complete proteins are cereals with a score of 0.59, and whole wheat with a score of 0.42.
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Best Food Choices
Foods containing complete proteins require whetting for their protein content, along with the calories and fat it provides to determine whether they make for good food choices.
A large egg provides 6 g of protein, 78 calories, including 48 calories from fat, and about 5 grams of fat. The egg white alone contain 3.6 grams of protein with only 16 calories and just 1 calorie from fat. Eggs make for the best complete protein food as they are rich in choline that reduces inflammation, ensures the integrity of cell-membranes and ensures adequate supply of the critical folic acid which maintains cardiovascular health. Studies supported by U.S. Department of Agriculture also link egg consumption with reduced risk of muscular degeneration and cataracts, all the while keeping cholesterol in check..
One cup (172 g) of soybeans contains 28.6 g of proteins, but provides 298 calories including 139 calories from fat, and about 15 g of fat. Soy is a wonder food as it provides much of the benefits of meat without its side effects. It contains active isoflavone compounds such as genistein that produce fewer and smaller fat cells, helping people stay lean. It lower blood pressure and cholesterol, promoting larger and less dangerous LDL. It may also promote bone density, especially in women.
Pure 100 percent whey protein powder provides 120 calories, including 18 calories from fat and 2 g of fat, while providing 23 g of protein. Whey helps manage weight better, helps in the fight against diseases such as cancer and diabetes and improves cardiovascular health.
One 4-oz serving of chicken breast provides 35 g of protein, 187 calories, including 36 calories from fat, and 4.1 g of fat. The same quantity of lean ground beef or tuna provides 22 g of protein, 160 calories, including 72 calories from fat, and 8 g of fat. The same quantity of roasted turkey breast provides about 20 g of proteins, 131 calories, including 28 calorie from fat, and 3.3 g of fat. Chicken contains rich quantities of niacin that protects against cancer, Alzheimer's disease and age-related cognitive decline, and vitamin B6 responsible for energy protection and cardiovascular health. Turkey is low in glycemic index.
Among dairy products, 1 oz. of cheddar cheese contains 7 g of protein, and provides 114 calories, including 84 calories from fat, and 9.4 g of fat. In contrast 1/2 cup of cottage cheese (113 grams) provides 16 g of proteins and only 82 calories, including 11 calories from fat, and 1.2 g of fat. One 170 g serving of low fat yogurt provides 5 g of protein, 100 calories and zero grams of fat. One ounce of skimmed milk, in contrast, provides 1 g of protein, 10 calories and no fat.
Among fish and seafood, one 165 g can of tuna fish contains 42 g of protein, and comes with 191 calories, including 12 calories from fat, and just 1.4 g of fat. Tuna is rich in important minerals such as selenium, magnesium, potassium, B vitamins, such as niacin, B1 and B6, and beneficial omega-3 essential fatty acids. Two servings of tuna each week provides more omega 3 than daily fish oil supplementation.
From the above list, good ingredient options for a complete, protein-rich meal are 2 to 3 oz. of cooked lean meat, poultry or fish, such as tuna. An alternative serving is one egg with 2 tablespoon of peanut butter or 1 oz. of cheese. Consume two to three servings per day, or as recommended by a dietician. The selection of the best food however depends on individual caloric requirements, which depends on the calories burned and growth requirements.
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The theory of protein combining or protein complementing that recommend consumption of certain complementary foods such as beans and rice together in the same meal, so that plant foods with incomplete essential amino acid content combine to form a complete protein and meet all amino acid requirements provided by complete proteins are now discredited. Vegans lacking in complete proteins may consume protein supplements to bridge the deficiency.
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- MedicinePlus. “Protein in Diet.” http://www.nlm.nih.gov/medlineplus/ency/article/002467.htm.%20Retrieved%20July%2010, 2011.
- USDA National Nutrient Database. http://www.nal.usda.gov/fnic/foodcomp/cgi-bin/nut_search_new.pl
- WHFoods. "Eggs." http://www.whfoods.com/genpage.php?tname=foodspice&dbid=92#healthbenefits. Retrieved July 10, 2011.