Whey protein is a byproduct of cheese making, derived from the watery part of milk that separates from the curds. It is used as a protein supplement for athletes, especially those involved in strength training, because it provides essential nutrients and amino acids. People who are lactose intolerant or allergic to other protein sources like eggs or soy also use whey protein. Research shows that combining whey protein with strength training can increase muscle strength, size, and lean body mass. It may also help prevent excessive weight loss in people with HIV. In young children, whey protein might help prevent conditions like eczema, but more research is needed. Always consult a healthcare provider before giving whey protein to children. The optimal dosage of whey protein is not established and can vary widely between products, so it's important to discuss any supplement use with a doctor, especially for pregnant or breastfeeding women.