Low Carb Dieting

If you are exercising, it is imperative that you fuel your muscles. The best way to do this is by ensuring that you eat adequate amounts of carbohydrates. I am not sure why it began, but the myth that carbohydrates are fattening is just that - a myth. As I have said before, carbohydrates are not fattening, excess calories are. Athletes are especially dependent upon carbohydrates as their muscles are constantly being used and depleted of glycogen. When you exercise hard, glycogen stores in your muscles are the main source of energy. You also have stored carbohydrates in your liver and blood (blood glucose). The liver glycogen is broken down and feeds into the bloodstream to feed your brain and muscles as well as maintain blood glucose levels. This is significant because those who are avoiding carbohydrates aren't able to maintain glycogen levels - thus directly decreasing the length and intensity of their workout. In a 2007 study, researchers had cyclists maintain a specific pedal speed until fatigue on two occasions. The first was after a 3 day low-carb diet in which they averaged about 75 minutes. The same cyclists then followed a 3 day high-carbohydrate diet and repeated the workout. This time, fatigue didn't set in until nearly 130 minutes. In conclusion, the researchers suggested that the increased glycogen levels were associated with improved performance and energy homeostasis (Green et al. 2007). It is worth noting that trained muscles have the ability to store about 20 - 50% more glycogen than that of untrained muscles (Sherman et al. 1981). I cite this because if you are just starting to exercise, simply eating a ton of carbs doesn't necessarily mean you will have incredible workouts. Rather, the take home message here is that your muscles will adapt to the training so that significantly more carbohydrates can be stored in your muscles and later used as energy. To wrap up, most exercise and health professionals suggest 55-65% of total kcals from carbohydrates for athletes. This will ensure that you are both adequately fueled for your workouts and able to replenish glycogen after exercise.

References:
Green, H., M. Ball-Burnett, S. Jones, and B. Farrance. 2007. Mechanical and metabolic
responses with exercise and dietary carbohydrate manipulation. Medicine & Science in Sports & Exercise

Sherman, W., D. Costill, W. Fink, and J. Miller. 1981. Effect of exercise-diet manipulation
on muscle glycogen and its subsequent utilization during performance. Int J
Sports Med 2:114-118.
39(1):139-148.