Which statement best defines a complete protein?

• A. Contains all essential amino acids
• B. Derived only from animal sources
• C. Contains no fats
• D. Provides energy only

Answer: (A)

A complete protein provides all nine essential amino acids in sufficient amounts for the body to use. Essential amino acids are those the body cannot make on its own, so they must come from the diet. When a protein contains all of them in adequate proportions, it supports growth, tissue repair, and maintenance effectively. While animal proteins are typically complete, some plant sources—like soy and quinoa—also qualify, though many plant proteins are incomplete on their own and may need to be combined with other foods. The concept isn’t about fats or energy delivery; proteins can contribute energy, but that isn’t what defines completeness. The statement that best defines a complete protein is that it contains all essential amino acids.