The key differences between complete and incomplete proteins lie in their amino acid profiles. Complete proteins contain all nine essential amino acids necessary for human health, typically found in animal products such as meat, fish, eggs, and dairy. In contrast, incomplete proteins lack one or more of these essential amino acids, often found in plant-based sources like legumes, grains, and nuts. To obtain all essential amino acids from an incomplete protein source, combining foods, such as rice and beans, can ensure a complete amino acid profile for optimal health and nutrition.