Proteins perform many critical functions in the body, including:

1. Tissue growth and repair: Proteins are essential for the growth and repair of body tissues, including muscle, skin, and bones.
2. Enzyme production: Enzymes are proteins that catalyze chemical reactions in the body, helping to break down and transform substances.
3. Hormone production: Some hormones, such as insulin, are proteins that regulate many physiological processes in the body, such as blood sugar regulation.
4. Immune system function: Antibodies, which are proteins produced by the immune system, help to identify and fight infections and diseases.
5. Energy production: In times of low carbohydrate availability, the body can break down proteins into glucose for energy production.

Sources of proteins include:

1. Meat and poultry: Beef, pork, chicken, turkey, and other meats are excellent sources of protein. They are also good sources of iron, zinc, and vitamin B12.
2. Fish and seafood: Fish, shellfish, and other seafood are also good sources of protein, as well as omega-3 fatty acids and other essential nutrients.
3. Eggs and dairy products: Eggs, milk, cheese, and yogurt are all good sources of protein. They are also good sources of calcium, vitamin D, and other important nutrients.
4. Legumes and soy products: Beans, lentils, chickpeas, and soy products such as tofu and tempeh are good sources of protein for vegetarians and vegans.
5. Nuts and seeds: Nuts and seeds, such as almonds, walnuts, peanuts, and chia seeds, are also good sources of protein. They are also a good source of healthy fats, fiber, and other nutrients.