The primary difference between a complete protein and an incomplete protein lies in their amino acid profiles. Complete proteins contain all nine essential amino acids that the body cannot synthesize on its own, and are typically found in animal products (e.g., meat, dairy, eggs). In contrast, incomplete proteins lack one or more essential amino acids and are usually found in plant sources (e.g., beans, grains, nuts). Understanding this distinction is important for forming balanced diets, especially for vegetarians or vegans seeking adequate protein intake.