Which plant protein is considered a complete protein with essential amino acids close to or over requirement?

• A. Soy
• B. Rice
• C. Wheat
• D. Corn

Answer: (A)

A complete protein provides all nine essential amino acids in amounts that meet or exceed what the body needs. Among plant foods, soy stands out because its protein contains all nine essential amino acids in balanced, adequate amounts, giving it a high-quality amino acid profile comparable to animal proteins (often described as having a PDCAAS of 1.0). That’s why soy is considered a complete plant protein and the best fit for this question. In contrast, rice, wheat, and corn each have limiting amino acids when eaten alone—for example, rice is relatively low in lysine, corn is low in lysine and tryptophan, and wheat is low in lysine—though combining them with other foods can create a complete pattern.