Fermented dairy products like kefir are a little-known magic bullet for muscle building. Kefir is the perfect addition to any muscle-building blender bomb, providing distinct nutritional advantages over water or regular milk. If you usually use water in your shakes, 1 cup of kefir will add 150 calories to your diet. Compared to regular milk, kefir will allow your meal to be more easily digested due to the presence of probiotics (up to 10 billion good bacteria per cup). These healthy bacteria will help keep your digestive track running at peak condition so it can break down and assimilate a maximum amount of calories and nutrients from your meals.