Quality and Quantity

Nutritionists use two criteria in evaluating protein sources: quality and quantity. Quality refers to the useability of protein by the body (not all of them can be used). This factor is expressed on a scale of 0 to 100. Quantity is the proportion of useable protein to total weight and is expressed as a percentage. The United Nations World Health Organization (WHO) gives meat a protein quality rating of 67—higher than that of most plant proteins, with the exception of whole rice (70), but below that of cheese (70), fish (80), milk (82), and eggs (95). In terms of quantity, 20 to 30 percent of the total weight of flesh food is useable protein—lamb rates the lower figure and turkey the higher one—the rest is water, fat, and trace minerals. On the other hand, soybean flour is 40 percent protein; Parmesan cheese, 36 percent; many nuts and seeds between 20 and 30 percent; and peas, lentils, and dried beans, between 20 and 25 percent. Grains are fairly low in quantity but, surprisingly, so are milk (4 percent) and eggs (13 percent).CD-SG 37.8

(There are other rating systems for food protein, also. The Food and Drug Administration uses a protein efficiency ratio [PER] as a quality standard for protein in nutritional labeling. Foods, such as meat and eggs, which are above a 2.5 PER, are considered excellent sources of protein; those, such as vegetables, which are below a 2.5 PER, are considered poor sources. The National Livestock Meat Board rates meats, both raw and cooked, on the basis of protein quantity. A serving of broiled, lean round steak is 31 percent protein; raw, the same piece of meat contains 22 percent. Choice-grade leg of lamb, cooked, is 25 percent protein; raw 18 percent.)CD-SG 38.1

What all this means is that, in general, one has to eat proportionately less meat in order to obtain the same amount of useable protein than if relying on vegetable sources, but that nonflesh alternatives are perfectly adequate. Balanced against this, however, are the disadvantages of a heavily meat-laced diet.CD-SG 38.2

The first problem most American meat eaters face is not a deficiency of proteins, but an excess. Nutritionists have established that a 154-pound man needs 43.1 grams of useable proteins, and 2,800 calories per day for adequate nutrition; a 128-pound woman also needs 43.1 grams of protein, but only 2,000 calories.CD-SG 38.3