Which statement describes an incomplete protein source?

• A. Animal source with all the essential amino acids
• B. Complete protein from animal products
• C. Plant source that doesn't have all the amino acids we need
• D. Soy contains all nine essential amino acids

Answer: (C)

Proteins are graded by whether they provide all nine essential amino acids in adequate amounts. An incomplete protein is one that lacks one or more of these essential amino acids. The plant-based option described as not having all the amino acids we need fits this idea, since many plant foods are missing or have insufficient amounts of one or more essential amino acids. In contrast, animal sources and animal-derived proteins are typically complete, and soy is commonly cited as a complete plant protein because it contains all nine essential amino acids. Remember, you can still obtain a complete amino acid profile on a plant-based diet by combining different plant proteins or choosing inherently complete plant options like soy, quinoa, or buckwheat.