Protein is required for muscle growth and tissue repair. Although protein is found in a variety of foods, supplemental shakes provide easy access to protein. Shakes come in an assortment of flavors and can be mixed with liquids including milk or water. Protein shakes with milk contain more calories than those made with water and are better if you are trying to gain weight. Avoid milk-based shakes if you are trying to lose weight. Always consult a doctor before starting a new diet.
According to "Nutrition for Health, Fitness and Sport" by Melvin H. Williams, protein is comprised of 20 amino acids. Eight essential amino acids must come from your diet, while 12 of them naturally form in your body. Protein sources vary in amino-acid content. Animal sources are complete proteins that contain all eight amino acids, while plant sources are incomplete and lack at least one amino acid. Plant sources can be combined to form complete proteins.
Protein shakes are formulated as complete proteins. Whey protein shakes are made with milk products, while soy protein shakes are plant based. According to "Nancy Clark's Sports Nutrition Guidebook," shakes allow you to consume a complete protein without making a meal or creating plant-based protein combinations. Some shakes provide additional vitamins and minerals.
Milk comes in whole, reduced-fat and fat-free varieties; therefore, the choice of milk impacts protein-shake content. One cup of whole milk contains 146 calories; a cup of 2 percent milk contains 122 calories; and fat-free milk has 83 calories per cup. Due to fortification, most milk varieties provide 8 g of protein per cup. Therefore, milk will add calories and protein to your shake, while water provides no additional nutrients. Protein shakes are complete proteins with or without the addition of milk.
According to the National Strength and Conditioning Association, an average adult requires 0.8 g of protein per kg of body weight while an individual doing strength-training needs 1.5 to 2 g of daily protein per kg of body weight. Although your body requires protein, excess protein is not beneficial. The body either converts the excess protein into fat -- and stores the fat -- or it expels it without using it.
Mayo Clinic nutritionist, Katherine Zeratsky, R.D., L.D., notes that relying on protein shakes instead of regular meals can cause you to lose out on the nutritional benefits of whole foods. "As long as you're eating a healthy diet, adding extra protein — either through protein shakes or other sources — isn't necessary," Zeratsky notes.