Whey protein is one of the two proteins found in cow’s milk. When milk is used to produce cheese, the curding process separates the curds from the liquid, also known as whey. Whey is a nutrient-dense, nearly translucent liquid consisting of all nine essential amino acids (the building blocks of protein) and vitamins and minerals. The liquid whey is filtered and dried to make whey protein powder.

Whey protein powder is often used as a nutritional supplement, and it can be added to smoothies, shakes, protein bars and balls, meal replacements and more. Because whey is dairy-based, it is not a vegan product. You’ll want to look for a plant-based protein powder instead, such as soy, hemp, pea or rice, if you are following a vegan diet.

Protein is vital for gaining muscle mass, and there is a lot of evidence to back this up, including a 2019 study in the Journal of Exercise Nutrition & Biochemistry. Eating enough protein may also help prevent muscle loss due to aging. According to a 2020 review in Experimental Gerontology, whey protein has been shown to be a good protein option for the aging population. From a medical standpoint, whey protein may also be used as a protein source for providing extra nutrition to people who have illnesses and need to gain body weight, as well as for healing wounds after an injury or surgery, according to a 2020 review in Nutrients.

Generally speaking, you want to try to get enough protein from the foods you eat in meals and snacks, including both animal and plant-based proteins, such as meat, poultry, fish, eggs, tofu and legumes. However, from amateurs to professional elites, physically active people may try whey protein to improve their athletic performance and gain muscle strength and mass. In this situation, whey protein is extra protein added to their existing diet.