Final answer:
Incomplete proteins are primarily found in plant-based foods like grains, nuts, and beans. These foods can be combined to form complementary proteins that provide the full range of essential amino acids. Examples include rice and beans or peanut butter on whole wheat bread.
Step-by-step explanation:
Foods that primarily offer incomplete proteins are plant-based sources such as grains, nuts, and beans. Unlike animal proteins which generally provide a complete set of all nine essential amino acids, plant proteins often lack one or more of these amino acids, making them incomplete. However, this can be remedied by combining different plant foods that offer complementary proteins. Examples of such combinations include rice and beans or peanut butter on whole wheat bread, which when eaten together, provide all the necessary amino acids that the body requires for proper functioning.
It is also possible to create a complete protein source by adding a small amount of animal protein to a meal, such as adding cheese to pasta. Since different foods can have different limiting amino acids, the concept of complementary proteins is important for those whose diet consists mainly of plant-based foods, especially for vegetarians and vegans who need to ensure they receive all the essential amino acids.