Which statement correctly defines complete proteins?

• A. Proteins lacking amino acids
• B. Proteins with all essential amino acids
• C. Proteins derived exclusively from plants
• D. Proteins that are not used for growth

Answer: (B)

Complete proteins provide all essential amino acids in adequate amounts. Essential amino acids are the ones the body can’t make, so they must come from the diet; a complete protein supplies every one of them in sufficient quantity, supporting growth and tissue repair. Animal foods like meat, eggs, dairy, and fish are classic complete proteins, and some plant sources—such as soy and quinoa—also provide a complete amino acid profile. Incomplete proteins lack one or more essential amino acids or don’t provide them in enough amounts, which is why combining plant proteins (like rice and beans) can help achieve a full amino acid mix. The other ideas aren’t correct: proteins aren’t defined by “lacking amino acids,” complete proteins aren’t restricted to plants, and they are indeed used for growth.