Which statement best defines incomplete proteins?

Incomplete proteins are those that lack one or more of the nine essential amino acids necessary for human health. Essential amino acids are those that the body cannot synthesize on its own and must be obtained through the diet. Incomplete proteins are typically found in plant-based sources such as grains, legumes, nuts, and seeds. They are essential in a balanced diet, but they do not provide all the amino acids required for protein synthesis, making it important for individuals consuming these sources to combine them in ways that together provide a complete amino acid profile.

In contrast, complete proteins contain all nine essential amino acids and are generally derived from animal sources. Thus, options that mention exclusive sources like only animal products or dairy do not accurately reflect the full scope of incomplete proteins. Additionally, stating that they provide all necessary proteins contradicts the very definition of incomplete proteins, as they do not fulfill the requirement of all essential amino acids.