The confusion is real when deciphering why it’s OK and even encouraged to fuel with sugar during a run, but it’s not OK to eat simple sugar any time you want. What’s the difference? There’s a big difference.
The body runs on various energy systems, and at any given time, we are always burning a percentage of both fat and sugar. The lower the output, such as sleeping, the higher the percentage of fat utilized. The higher the output, such as running all-out repeats on the track, the more sugar we burn. An easy, aerobic run that is fully conversational will utilize approximately 50 percent carbs and 50 percent fats.
During an interval run, you may go from aerobic to anaerobic and back to aerobic efforts, drastically changing from one metabolic system to the next, which utilizes glucose pulled from stored glycogen – quickly. Therefore the sugar consumed during this run will be broken into glucose rapidly since there’s no protein or fat to slow down gastric emptying, turned into blood glucose, and quickly taken up by the working cells for energy.
In layman’s terms, the sugar you consume in training and racing is immediately used for energy and will enhance your performance.
Sugar can also restock glycogen storage and spur along recovery when consumed after running long distances or intense workout. If glycogen stores aren’t refilled after depletion, it puts the body under stress, increasing cortisol. In turn, muscle is broken down for energy, the very thing the runner wants to avoid.
However, when the body is at rest while sitting at your desk or watching a movie, it is burning primarily fat. During this state, the muscle cells are not working hard and don’t need to utilize sugar for quick energy. So, the sugary snacks consumed, in this case, will be converted to fat for storage and future use.