What is an incomplete protein?

An incomplete protein is defined as a protein source that lacks one or more of the essential amino acids necessary for the body's needs. Essential amino acids are those that cannot be synthesized by the human body and must be obtained through the diet. Most animal-based proteins are complete, meaning they contain all of the essential amino acids. In contrast, many plant-based proteins can be considered incomplete because they may not provide the full range of these amino acids in sufficient quantities.

For example, grains and legumes are often cited as incomplete proteins since they may be low in certain essential amino acids. However, by combining different plant-based protein sources, such as beans and rice, one can create a complete protein profile, providing all essential amino acids. This understanding is vital for meal planning, especially for those following vegetarian or vegan diets, to ensure they obtain adequate nutrition.

The other options do not accurately define an incomplete protein. Proteins with all essential amino acids represent complete proteins, while a protein being solely plant-based does not inherently indicate its completeness. Additionally, calorie content does not determine whether a protein is complete or incomplete; it merely refers to the energy value of the food.