A complete protein is one that contains all nine essential amino acids required for human health. This is particularly relevant in dietary sources, as certain foods lack one or more of these amino acids. Complete proteins are typically found in animal products, including meat, dairy, and eggs. However, plant-based sources like quinoa, soy, and chia seeds also qualify as complete proteins. Understanding the distinction between complete and incomplete proteins is vital for optimizing dietary protein intake, particularly for those on vegetarian or vegan diets.