Which statement best describes a complete protein in human nutrition?

• A. A protein that provides all essential amino acids in sufficient amounts to meet human dietary requirements
• B. A protein that cannot be digested and therefore contributes no amino acids to the body
• C. A protein that is composed entirely of branched-chain amino acids (leucine, isoleucine, and valine)
• D. A protein that contains only essential amino acids and no nonessential amino acids

Answer: (A)

Verified step by step guidance

1. Understand the definition of a complete protein in human nutrition: it refers to a protein source that contains all the essential amino acids in adequate amounts necessary for human dietary needs.
2. Recall that essential amino acids are those that the human body cannot synthesize and must be obtained from the diet.
3. Recognize that a protein that cannot be digested does not contribute amino acids to the body, so it cannot be considered complete in nutritional terms.
4. Note that a protein composed entirely of branched-chain amino acids (leucine, isoleucine, and valine) is not complete because it lacks other essential amino acids.
5. Understand that a protein containing only essential amino acids and no nonessential amino acids is not a requirement for completeness; the key is having all essential amino acids in sufficient amounts, regardless of nonessential amino acid content.