The difference between complete and incomplete proteins lies in the amino acid profiles they provide. Complete proteins contain all nine essential amino acids required by the body and are primarily found in animal sources like meat, dairy, and eggs. In contrast, incomplete proteins lack one or more essential amino acids and are usually derived from plant sources, such as beans, nuts, and grains. Combining different plant-based proteins can ensure all essential amino acids are consumed for those following a vegetarian or vegan diet.