In the diet, protein sources are labeled according to how many of the essential amino acids they provide: A complete protein source is one that provides all of the essential amino acids. You may also hear these sources called high-quality proteins. Animal-based foods; like meat, poultry, fish, milk, eggs, and cheese are considered complete protein sources. An incomplete protein source is one that is low in one or more of the essential amino acids. Complementary proteins are two or more incomplete protein sources that together provide adequate amounts of all the essential amino acids.
For example: Rice contains moderate amounts of certain essential amino acids; however, these same essential amino acids are found in greater amounts in dry beans. Similarly, dry beans contain lower amounts of other essential amino acids that can be found in larger amounts in rice. Together, these two foods can provide adequate amounts of all the essential amino acids the body needs.
Here are examples of amounts of protein in food: •1 cup of milk has 8 grams of protein •A 3-ounce piece of meat has about 21 grams of protein •1 cup of dry beans has about 16 grams of protein •An 8-ounce container of yogurt has about 11 grams of protein Added together, just these four sources would meet the protein needs of an adult male (56 grams). This doesn't count all the other foods that add smaller amounts of protein to his diet.
To help you make lower-fat protein choices -- •Choose meats that are leaner cuts and trim away any fat you can see. For chicken and turkey, remove the skin to reduce fat. •Substitute pinto or black beans for meat in chili and tacos. •Choose low-fat or fat-free milk and yogurt. •Choose low-fat or fat-free cheese. •Choose egg whites or pasteurized egg white products. What if I am a vegetarian? Because some vegetarians avoid eating all (or most) animal foods, they must rely on plant-based sources of protein to meet their protein needs. With some planning, a vegetarian diet can easily meet the recommended protein needs of adults and children.
Sources 1 The position of the American Dietetic Association and Dietitians of Canada: Vegetarian diets. JADA, 2003; 103(6) 748 – 765.
Source 2 for Acceptable Macronutrient Distribution Range (AMDR) reference and RDAs: Institute of Medicine (IOM) Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. This report may be accessed via http://www.nap.edu/*