What is a characteristic of incomplete proteins?

Incomplete proteins are those that do not provide all nine essential amino acids in sufficient quantities needed by the body. Essential amino acids are those that the body cannot synthesize and must be obtained through diet. Incomplete proteins typically come from plant sources, such as grains, legumes, nuts, and seeds. Because they lack one or more of these essential amino acids, they are often considered less ideal for meeting protein needs on their own.

In contrast, complete proteins, which are primarily found in animal products, contain all essential amino acids in adequate amounts. The incorrect answer choices reflect misunderstandings about protein composition. For instance, stating that incomplete proteins contain all essential amino acids contradicts their very definition. Similarly, rigidity regarding the sources of incomplete proteins, suggesting they are only sourced from animals, is wrong since they primarily come from plants. Lastly, the idea that they are easily digestible does not accurately describe them either, as digestibility can vary depending on the type of protein and the source. Thus, recognizing that incomplete proteins lack one or more essential components is crucial in understanding protein quality in nutrition.