Essentials of Nutrition for Sports

Plant Protein

Plant sources of protein (grains, legumes, nuts, and seeds) are

generally deficient in one or more essential amino acids.

The exception is the soybean; all essential amino acids are

present.

Protein synthesis occurs only to

the extent that the limiting

amino acids are available.

If they are relatively low, but not lacking in a limiting amino

acid, they can meet the requirements for essential amino acids if ingested in large quantities.

Different plant proteins can also be combined to provide

amounts and proportions of essential amino acids equivalent to high biological proteins from animal sources. This is discussed in more detail below.

Such proteins are considered to

have intermediate biological

value or to be

partially complete

.

Plants that are entirely lacking in one or more essential amino

acids are considered of low biological value or to be

incomplete

.

These sources include most fruits and many vegetables.

A low biological value also means that it is difficult or

impossible to compensate for insufficient amounts of essential amino acids by combining different sources as with partially complete proteins.

Examples of high-, intermediate-, and low-quality proteins are

listed in

Table 8

.

High/Complete

Intermediate/Partially Complete

Low/Incomplete

Milk, cow

Soy

Peas

Eggs, chicken

Sunflower seeds

Cornmeal

Milk, human

Rice

Flour, white wheat

Beef

Potatoes

Cassava

Fish

Oats

Gelatin

Peanut

butter

Beans

Table 8. Protein quality. Examples of high-, intermediate-, and low-quality proteins.

Combining Complementary Proteins

Vegetarians and others often de

pend upon incomplete proteins

such as nuts, grains, and legumes.

By eating a balanced diet of grains and legumes with each meal

or over the course of each day incomplete proteins can be combined to provide all amino acid requirements.

For example:

-^

The amino acids from beans taken at one meal can complement the amino acids from rice eaten at another meal that day.

-^

Macaroni complements cheese. The essential amino acids from the cheese allow the body to better use the amino acids in the macaroni.

-^

Peanut butter complements wheat bread.

Amino Acid Score

The amino acid balance concept:

-^

Protein synthesis is limited unless all amino acids are present in appropriate amounts.

-^

Protein synthesis is limited by the essential amino acid present in the least amount in relation to the amount required.

Nutrition for Sports, Essentials of 59