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Fuel Your Body for Optimal Performance

By Mary Dinehart-Perry

For anyone going into the field of dietetics it is a prerequisite to take biochemistry. You sit in class wondering who would ever ask you to explain how the food you eat turns into the chemical energy known as ATP via the Krebs cycle, oxidative phosphorylation, and the electron transport chain… Probably not many!

Putting the biochemistry lecture aside, how the body uses the food you eat to make energy is critical when it comes to athletic performance. Most athletes are of the belief that you need to consume a high carbohydrate, low-fat diet for optimal performance, however, when you look into the biochemistry of how much energy is produced from carbohydrates versus fat you may want to rethink how you fuel your body for optimal performance.

One of the simplest breakdown products of carbohydrate is glucose. To make it easy to understand, for every 1 mole of glucose, the body generates a maximum of 36-38 moles of ATP under aerobic conditions. Under anaerobic conditions, the ATP generation drops to about 2 moles of ATP per mole of glucose. Keep in mind that during a typical triathlon, the athlete operates below the anaerobic threshold due to the length of the competition. For fat, pending the length of the fatty acid chain, you may be able to generate as much as 106 moles of ATP per fatty acid.  It doesn’t take a biochemist to tell you that you get almost three times the amount of energy from fat that you do from carbohydrate. Think of fat as high octane fuel.

Carbohydrates definitely have a role in athletic performance as certain tissues rely solely on them for fuel (i.e., the brain), but if the majority of your diet is carbohydrate-based. The body is not able optimize the high octane fuel that fat potentially provides. This is because the high levels of insulin generated by a carbohydrate-rich diet block the release of ATP production from the fat tissue. Furthermore, the body relies on the balance of the hormones insulin and glucagon to either store the food at each meal for energy later or to use it immediately when glucose levels in the blood are low. After ingestion of carbohydrates, insulin is released promoting the storage of glucose into glycogen in liver and muscle, or converting glucose to triglycerides for storage in fat. Glucagon levels are low after a high carbohydrate meal, but a higher protein meal stabilizes or even increases glucagon levels. During a fasting state (like competing in a triathlon), glucagon helps to maintain energy levels by stimulating the release of glucose from glycogen or from other sources. When the level of glucagon relative to insulin is high, fatty acids are mobilized from fat tissue for energy (1).

So what does all of this mean for you the triathlete? The composition of each meal plays a huge role in the amounts of insulin and glucagon in the blood after a meal. A high carbohydrate meal raises insulin and lowers glucagon, but the level of protein stabilizes glucagon and even allows for fat to be used for energy. Ideally you want to balance carbohydrates and protein so that the levels of insulin are not too high that you can’t use fat for energy, but not too low that your cells don’t get the glucose they need to survive. For ultimate athletic performance and getting the most bang for your buck with regards to energy utilization, an ideal diet leading up to race day would be one in which every meal and every snack is moderate in carbohydrate (40%), protein (30%), and fat (30%). This diet would ideally be comprised of lots of fruits and vegetables, lean proteins, and good fats like those found in olive oil, nuts and seeds. 

1. Marks D., Marks A., Smith C. (1996).  Basic Medical Biochemistry: A Clinical Approach.  Philadelphia: Lippincott Williams & Wilkins.