Final answer:
Complete proteins, containing all nine essential amino acids, are primarily found in animal products like meat, fish, milk, and eggs, while plant sources often require combining different foods to make complete proteins.
Step-by-step explanation:
Foods that primarily offer complete proteins are those which contain all nine essential amino acids needed by the body. Animal proteins such as meat, fish, milk, and eggs are excellent sources of complete proteins. These proteins are crucial for maintaining muscle tissue, and they also function as enzymes, hormones, and antibodies in the human body. Plant-based proteins often lack one or more of these essential amino acids, making them incomplete proteins. However, combining different plant foods, known as complementary proteins, can provide all necessary amino acids. For instance, grains can be paired with legumes to form a complete protein profile, which is especially important in vegetarian and vegan diets.
There are also manufactured sources of proteins, such as protein powders that come from casein, whey, egg, rice, soy, and cricket flour. It's important to note that excessive protein intake can lead to the extra calories being stored as fat in the body.