What are the basic purposes of food? Food provides energy, food regulates metabolic processes, and food supports growth and development.
Sport nutrition may be viewed in two ways:
1. Nutrition for training - All three purposes of food are taken into account with training
2. Nutrition for competition - Prime importance of food is energy and regulating metabolic processes
During your training period, due to the increase in energy expenditure, you need to increase your calorie intake to maintain your bodyweight and to help your body make adjustments in becoming more efficient. For example, you will be forming new body tissue.
Another example that has long been known to effect long distance runners is an increase in hemoglobin content in the blood. Hemoglobin is a protein in our red blood cells responsible for picking up and dropping off oxygen throughout our body. The key to hemoglobin is iron (4 irons per hemoglobin) and is the actual element that "picks up" the oxygen. This translates to a daily diet needing to "contain adequate amounts of iron not only to meet normal needs but also to make effective body adjustments due to the chronic effects of training."
In competition an athlete will utilize specific body energy sources and systems, depending up the intensity and duration of the exercise. For short, high intensity exercise, our bodies will use stored carbohydrates in our muscles anaerobically. This can last up to one to three minutes. During endurance exercise, lasting longer than five minutes, we use aerobic respiration that oxidizes stored carbohydrates (glycogen) and fats in our bodies. So you need to have enough of those carb & fat energy stores to satisfy the energy demands of exercising for long periods of time.
Contrary to what people may think, protein is not generally used to provide the energies needed for exercise. Don't get me wrong, protein is extremely important in our bodies, but we use it for all of our other body functions, not typically energy storage. If you do not consume enough carbs, our body will convert proteins into energy, but then you are taking it away from all of the other jobs that only protein accomplishes. Some other negative side effects include breaking down muscle and raising blood acidity.
Your intake of protein during training doesn't need to be altered all that much. Since you will be consuming more calories in general (marathon trainers will consume around 700 - 1,000 extra calories!) you will probably get the additional amounts of protein anyways without having to try. If you want me to get particular, simply multiply your weight, in pounds, by one of the following:
- Active adult 0.4-0.6
- Growing athlete 0.6-0.8
- Adult building muscle mass 0.6-0.8
Lean beef, white-meat poultry, pork tenderloin, legumes/beans, eggs, nuts, yogurt, and seafood are all excellent sources of protein.
Information above was gathered from my textbook Nutrition for Health, Fitness, & Sport by Melvin Williams and Understanding Nutrition by Ellie Whitney and Sharon Rady Rolfes.