Proper nutrition is an essential element of athletic performance, body composition goals, and general health. Although natural variability among persons makes it impossible to create a single diet that can be recommended to all; examining scientific principles makes it easier for athletes and other physically active persons to eat a diet that prepares them for successful training and/or athletic competition. A proper nutritional design incorporates these principles and is tailored to the individual. It is important for the sports nutritionist, coach, and athlete to understand the role that each of the macronutrients plays in an active lifestyle. In addition, keys to success include knowing how to determine how many calories to consume, the macronutrient breakdown of those calories, and proper timing to maximize the benefits needed for the individual's body type and activity schedule. © 2008 Humana Press.