Protein powder is a popular nutritional supplement. Protein is an essential macronutrient that helps build muscle, repair tissue, and make enzymes and hormones. Using protein powder may also aid weight loss and help people tone their muscles. DHA is commonly used for heart disease and high cholesterol. It is also used for boosting memory and thinking skills, for aiding infant and child development, for certain eye disorders, and many other conditions, but there is no good scientific evidence to support these uses.