Nutrition Science and Everyday Application - beta v 0.1

PROTEIN IN FOODS AND DIETARY RECOMMENDATIONS 335
• Enjoy nuts in a variety of ways. Put them on a salad, in a stir-fry, or use them as a
topping for steamed vegetables in place of meat or cheese.
PROTEIN QUALITY
While protein is contained in a wide variety of foods, it differs in quality. High-qualitycomplete
proteins contain all nine essential amino acids. Lower-qualityincompleteincomplete proteins do not
contain all nine essential amino acids in proportions needed to support growth and health.
Foods that are complete protein sources include animal foods such as milk, cheese,
eggs, fish, poultry, and meat. A few plant foods also are complete proteins, such as soy
(soybeans, soy milk, tofu, tempeh) and quinoa.
Most plant-based foods are deficient in at least one essential amino acid and
therefore are incomplete protein sources. For example, grains are usually deficient in the
amino acid lysine, and legumes are low in methionine and tryptophan. Because grains and
legumes are not deficient in the same amino acids, they can complement each other
in a diet. When consumed in tandem, they contain all nine essential amino acids at
adequate levels, so they are called complementary proteins. Some examples of
complementary protein foods are given in Table 6.4. Mutual supplementation is another term
used when combining two or more incomplete protein sources to make a complete protein.
Complementary protein sources do not have to be consumed at the same time—as long as
they are consumed within the same day, you will meet your protein needs. Most people eat
complementary proteins without thinking about it, because they go well together. Think of a
peanut butter sandwich and beans and rice; these are examples of complementary proteins.
So long as you eat a variety of foods, you don’t need to worry much about incomplete protein
foods. They may be called “lower quality” in terms of protein, but they’re still great choices,
as long as they’re not the only foods you eat!