Soy protein is derived from the soybean plant and a good, although incomplete, source of protein. Soy protein products come in various concentrations and are available alone or in combination with carbohydrate and fatty acid constituents. Soy is added to many commercially prepared products ranging from baked muffins to protein bars to infant formulas. Additional amino acids can be added to soy products. Soy products are relatively inexpensive.
Whey protein is obtained during the processing of milk to cheese.
Whey is a complete protein. Exaggerated claims have been made that whey is the best source of protein by sellers of whey protein supplements. Although an excellent protein source whey is not better than meats or dairy products. Whey protein is generally more expensive than soy based protein. Soy and whey are the most common constituents of infant formulas.