The Bonk Series 2: Glycogen Loss During Training, Racing and Everyday Living
Glucose, fructose, maltodextrin, superstarch, simple carbs, complex carbs, good sugars, bad sugars, starch…the list goes on and on of forms of energy forms for us as athletes. It can certainly be overwhelming to figure out what is the best. The long answer involves a lot of science, but the short answer often comes down to what works best for you. As you compete in long and short distance races you will hear people discuss, adnauseum (no pun intended) what product they use and why. But just because that works for one person doesn’t mean it will work for you. The quantity in which those calories are needed is also up to each person and their metabolic needs.
It seems to me that in most athletic literature, glycogen is the new glucose. Funny thing is that glycogen is glucose for all intents and purposes. But glycogen is the storage form of glucose in your liver. Let’s take a small scientific step back and simplify everything. You eat a gel, the gel has maltodextrin and fructose. Or let’s say you eat a banana, it has glucose. So you consume your food/gel/liquid and and the breakdown to usable glucose begins. The mouth/saliva starts to breakdown your food and this is continued on in the stomach on to the intestines. As your food is broken down, it is transported through the digestive tract to the bloodstream. From there, some glucose is stored in cells making up your muscles, your liver and some in other tissues.
Glycogen is the storage form of glucose in the liver. Depending on the type of exercise, it may be your primary source of fuel. If you are a weight lifter and need quick bursts of energy, these glycogen stores will be broken down and available for your muscles to have glucose. If, however, you are an endurance athlete, these glycogen stores will last you about 2 hours or 1000-2000 calories worth and then you will bonk (see Blog 1) unless you replenish these stores or train yourself to use the 50,000-80,000 calories of fat we all have available as fuel.
Glucose and fructose are simple sugars, monosaccharides, more simply broken down. Sucrose is glucose and fructose combined.High fructose corn syrup is fructose and glucose with 55% fructose and 45% glucose. It has also been linked to a higher risk of metabolic syndrome. Ingestion of simple sugars will cause a quick spike in insulin to help shuttle the glucose molecules out of the bloodstream and into tissues.
The complex carbohydrate most common to us is maltodextrin. Another starch, newer to the market, is superstarch (Generation UCAN). Naturally occurring complex carbohydrates (whole grains) are supposed to be broken down more slowly, thus causing a more steady state level of glucose in your bloodstream instead of the common spikes in blood sugar and thus insulin that we see with simple sugars. Maltodextrin is used by a lot of athletes because it is still quickly absorbed through the digestive tract so it helps during a workout or in recovery. UCANsuperstarch is a newer product that was made to help kids with inborn errors of metabolism. It is now being used with great success in a lot of athletes, especially those trying to minimize calorie intake by becoming more metabolically efficient.
The long and the short of it is that there are a lot of different forms of glucose available to you to build your glycogen store in your liver and help your avoid bonking. When that storage of glycogen is depleted, either during training or racing, your body will need more fuel to supply the muscles with energy. Through trial and error you will be able to figure out which products, if any, meet your needs. For events lasting longer than an hour, if you are able to become more metabolically efficient (using your own internal fat stores for fuel) you may be able to train and race on minimal if any exogenous fuel needs.