What are the two main categories of proteins mentioned?

The two main categories of proteins are classified as complete and incomplete based on their amino acid profiles. Complete proteins contain all nine essential amino acids that the human body cannot synthesize on its own. These are typically found in animal products such as meat, fish, eggs, and dairy. In contrast, incomplete proteins lack one or more of these essential amino acids and are often derived from plant sources like grains, legumes, and nuts, which may need to be combined with other foods to ensure that all essential amino acids are consumed.

This classification is particularly relevant in discussions about nutrition, particularly for individuals following vegetarian or vegan diets, as understanding complete and incomplete proteins can help ensure they receive sufficient essential amino acids through proper dietary combinations. Other answer choices do not pertain directly to the amino acid composition of proteins: simple and complex refer to carbohydrate types, primary and secondary relate to the levels of protein structure, and animal and plant indicate sources of protein rather than their completeness in amino acid composition.