There is a concept out there called ‘carbo-loading’. We are told to eat extra carbohydrates in the day, or even the days, leading up to a long run. This can be achieved by either having more meals in the day or increasing your portion sizes per meal of eating bread, pasta, rice and the likes. These extras will be stored by your body and will be used during your run. On top of that, you won’t even get fat.
Let’s step back for a moment and examine this claim. It is likely, though not necessarily true, that these extra carbohydrates (carbs) will be stored somewhere on your body in one way or another as an energy source your body can use. However, there is also the possibility that it will go straight through you without being absorbed. This can happen when your gut is damaged (e.g. inflamed).
Now consider the type of carbs that are suggested: bread, pasta, rice, etc. All of these are mostly sugar. When you eat these, your blood will be flooded with sugar. Your body doesn’t like this spike. Mechanisms will work to get the level of sugar in your blood back to an acceptable level. The sugar will be transformed to a storage form. It can be stored in muscle or the liver as a readily accessible sugar, or becomes fat and is stored in fat cells. There is little storage space in the liver and muscles, so most will wind up as fat.
Unless you eat these carbs relatively close to your run, they are stored as fat well before you get to your run. Using these fat stores for energy is an option. There is however a problem. As long as you keep eating these carbs or any other sugary source like the abundant ‘gu’ or ‘gel’ then you won’t be able to access your fat stores and convert these to energy for your muscles.
Once you go down the path of eating carbs to fuel your run, you will be eating carbs constantly to meet your energy needs. As long as you can absorb these, it can work out and supply you with energy. Though, as the run gets longer and longer, your gut will start protesting this constant carb eating. This has now become an absorption issue. You are using energy while running. Your gut has difficulty in absorbing all that energy. You can’t access your fat stores for energy. Continuing will deplete you of energy, and that isn’t pretty. What starts lightheaded, can lead to medical intervention.
We don’t advocate any particular diet. We want you to be healthy and able to perform. What you do before your run matters as much as what you do during your run (maybe even more). Consider using your own fat stores to supply your energy needs. For one thing, you won’t have to lug around all those gels. That is quite freeing. Or think of all the money you save by not having to buy these overpriced goodies. Think about your diet as an ongoing experiment. Find out what works best for you.