An incomplete protein is defined as which?

• A. High quality, with all essential amino acids
• B. Low quality, deficient in one or more essential amino acids
• C. Provides all energy needs
• D. Derived from animal products only

Answer: (B)

Proteins are judged by whether they supply all nine essential amino acids in adequate amounts. An incomplete protein lacks one or more of these essential amino acids, making it a low-quality protein. Because the body cannot synthesize these essentials, relying on an incomplete protein alone can limit protein synthesis and tissue maintenance. The energy content of a protein isn’t what defines its quality; proteins can provide calories, but their usefulness for growth and repair depends on having all essential amino acids. Many plant proteins are incomplete on their own, though combining different plant sources can create a complete amino acid profile. Animal-derived proteins typically cover all essential amino acids as well, though there are exceptions among plant sources that do provide complete profiles.