In general, whey protein is advertised as a top performance enhancer for athletes/strength trainers. The general advantage of whey protein advertised by companies that process it is the speed that it travels to one's muscles after a workout (Also known as a fast digesting protein). Casein protein is referred to as a slow digesting protein. Both types of protein are components of milk. Milk is approximately 90% water. The remaining parts of milk are the proteins and carbohydrates. Out of the protein in the milk, 20% of it is whey protein and 80% of it is casein protein. Nutritionists emphasize the importance of both kinds of protein. Whey protein is used as an immediate source of protein, which is absorbed by the muscles quickly after consumption. Casein protein is a slow digesting protein, which is slowly absorbed by the muscles after consumption. The whole reason of manufacturing an entirely different product that separates the two proteins from the rest of the milk is the fact that the abundance of each individual protein is relatively low in the milk itself. Although the proteins both hold a low concentration in milk, it contains a high enough abundance of casein protein to be effective enough. A common serving size in whey protein powders is 30 grams. There are 8 grams of protein in a serving of milk and 16 servings in a gallon. Since only 20% of the 8 grams is whey protein, there are only 1.6 grams of whey protein in a serving of milk. This means that there are approximately 25.6 grams of whey protein in a gallon of milk. This shows that it would take an entire gallon of milk every day to consume not even an entire serving of whey protein recommended by nutritionists (30 grams). Drinking a whole gallon of milk a day would take away room in the stomach for other important foods in an athlete's/strength trainer's diet, such as other forms of protein, carbohydrates, and foods abundant in essential vitamins (Fruits, veggies, etc.