Justin Robinson, MA,RD,CSSD,CSCS
1.) Intake
This is the area of nutrition we have the greatest control over – the quantity and quality of foods and fluids you ingest is entirely up to you. Granted the types of food available on a race course or how much you can carry with you often limit choices, but proper education, planning, and, yes, self discipline will help you create fueling strategies to optimize intake. An enormous part of this strategy includes practice – always know how your body responds to certain foods and fluids and never try anything new on race day.
2.) Absorption
Fuel absorption depends greatly on how quickly foods leave your stomach (i.e. gastric emptying). Emptying rate depends on several factors including the composition of the fuel, volume of meals, and others including osmolality, temperature, acidity, and viscosity2. Fuel composition has the most significant effect – carbohydrates, fats and proteins have very different make ups which influence absorption rate. Generally speaking, carbohydrate digests the quickest while fat and protein stay in the stomach longer, slowing their digestion (highfiber foods also slow stomach emptying). Likewise, very large quantities of food increases digestion time, regardless of composition (that Thanksgiving meal may take hours to fully absorb). Also keep in mind that the body will not optimally absorb fuel or nutrients without water – so always hydrate before, during and after meals. The key, as further described below, is to focus on the slowerdigesting foods throughout most of the day and the quicker-digesting foods when fuel demands increase, such as right before, during and immediately after a workout
3.) Utilization
Once the body breaks down food in the stomach, the nutrients are absorbed in the small intestine and delivered to working muscles and the brain. The current needs of the body regulate utilization; i.e. exercise intensity and current “on board” fuels determine whether carbohydrate, fat, protein, vitamins and minerals will be used immediately or stored for later use. Carbohydrate and fat serve as the primary energy sources and are related to intensity – at low intensities (below 60% max) for example, a greater percent of our energy comes from fat stores. At high intensities we use more carbohydrate – above 90% max, we use almost exclusively carbohydrate. During most sporting events, especially endurance events, our body's supply of energy (both ingested and stored fuels) will not meet the demand, meaning we will eventually deplete our stores. This notion significantly increases the importance of post-exercise recovery nutrition.
