The other two are fats and carbohydrates.
Protein is used by the body to build, maintain, and repair body tissues.
There is little effect on blood sugar levels. Protein is in all animal foods and some plant foods, but in smaller amounts. Plant foods that have a fair amount of protein in them are pinto, kidney, and red beans, lentils, and split peas. Plant proteins are lower in fat than animal proteins. Try to eat lean meats and nonfat or skim milk products with dried beans and peas as your low-fat protein sources.