What is the possible limiting amino acid in vegetables?

• A. Lysine
• B. Methionine
• C. Tryptophan
• D. Valine

Answer: (B)

In plant proteins, the limiting amino acid is the essential one found in the smallest amount relative to what the body needs, and it governs how much protein can be made. In vegetables, sulfur-containing amino acids are often in short supply, so methionine tends to be the first essential amino acid that runs short. That makes methionine the most likely limiting amino acid when relying on vegetables for protein. Other amino acids like lysine, tryptophan, or valine can be adequate or only occasionally limiting in certain plant foods, but methionine is the typical bottleneck in vegetable protein. This explains why combining plant sources (such as grains with legumes) helps balance the profile and improve overall protein quality by supplying more methionine from grains while legume proteins provide other essentials.