How Much Sugar Can We Stomach?

The array of food at a typical aid station in today’s ultramarathon races is overwhelming. The choices become almost as hard to negotiate as some of the trails. Besides all the latest sports nutrition products, there is usually a mixture of salty snack foods, candy bars, cut-up fruit, sandwich quarters and the high-glycemic potato dipped in salt. What’s the best for quick energy – we just need sugar for our muscles, right? If we could stomach sucking down sugar cubes for a hundred miles, would that get us to the finish line in good shape? Well, almost no one can stand that much sugar for that many hours even if you finish with a fast time. And the best choice is not simple sugar, even though depleted glycogen levels are most obviously restored with glucose, a simple sugar. The reason has to do with the osmolality of our bodily fluids.

Osmolality is a measure of the total number of particles in a solution and the human body likes to maintain its body fluid osmolality at a constant level. If we ingest solutions that are too concentrated, such as products or foods that contain monosaccharide simple sugars (glucose, sucrose, dextrose) or disaccharides (maltose, fructose, lactose), our body will pull fluids and electrolytes from other areas and tissues of the body that may critically need them just to aid in the digestion of these highly-concentrated sugar mixes. This can result in loss of tissue fluids that are used in our body’s cooling mechanism -sweating. It can also create further problems with gas and cramping, not to mention dehydration, rather than adding to sustained energy for running. The situation can be avoided by mixing these simple sugars in a weak six – eight percent solution and that is why most sports drinks contain just such a percentage. But this resolution creates another problem; the number of calories is limited in this weaker solution. This concentration only provides about 100 calories per hour and that is inadequate for maintaining energy production in continually exercising muscles. Add more calories and the osmolality is raised. Add more calories and water, and the possibility of hyponatremia increases. A vicious cycle ensues.

In the mid-nineties, GU™ came on the market – a new product in the form of a gel that used maltodextrin, a complex carbohydrate, as its main ingredient instead of simple sugars. Maltodextrin is a glucose polymer, or polysaccharide, that can easily be absorbed from the intestine in a more concentrated, 15 – 20 percent solution. This provides up to three times as many calories while clearing the gut at the same rate as normal body fluids. This breakthrough provided endurance athletes with more calories absorbed at a faster rate and more easily than solid food. Other products soon came on the market and the result was more energy production in less time and reduced odds of a DNF.

With the advent of gels, several questions arise. Do we need “real” food anymore? Does maltodextrin grow on trees in a natural state? Yes and no. Yes, there is still room for real food and no – no “malto-trees”. There is still something to be said for comfort food. And there have been numerous studies showing that after many hours of continual exercise, some protein will help an athlete absorb an even greater amount of carbohydrate. Do you need to buy the commercial products? No, that is why there are all those food choices at the aid stations. Some are pre-packaged forms of complex carbohydrates, but some (potatoes and sandwiches) don’t travel as well in your pocket. Although it is possible to make your own maltodextrin mixture, energy gels and blocks do provide an easy to carry, easy to absorb and digest, quick-acting source of complex carbohydrate energy when you are racking up the miles. All you have to add is water, which makes you pretty self-sufficient and able to run through aid stations quickly without having to make too many decisions. They come in a variety of flavors and consistencies and some come with added ingredients such as electrolytes, vitamins and caffeine.

What about the glycemic index (GI) of glucose polymers? Maltodextrin may have almost the same high numeric number as simple sugars. Certainly when you are not running, the GI of foods can affect your health by causing an “insulin spike” and should be a consideration in your nutrition choices. But when you are exercising, this insulin reaction mechanism is mostly turned off and your body uses the calories for quick energy production, sending the sugars to your working muscles rather than letting them stay in the blood for a “spike”. More calories to the muscles equals more sustained energy (ATP production to drive muscles) and less chance of a bonk.

Scientific studies show that complex carbohydrates are the fuel of choice for the ultrarunner. The gels offer an advantage by providing more calories per hour than sports drinks and by being easier to absorb than sports bars or solid food. For the back-of-the-pack runners who will be on the trail for many more hours than the elite runners, this can translate into more energy without going into a caloric deficit state. For the lead pack runners who are pushing themselves at a very high intensity (above 90 percent), the advantage can be less stomach distress and more calories can be absorbed for more energy. For those who are just using the ultra as a training run or are taking it easy, go ahead and enjoy the smorgasbord at the buffet table. But if you want to have an even better time, try some complex carbohydrates and watch the simple sugars.



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Sunny Blende

Sunny Blende, M.S. is a Sports Nutritionist who writes and counsels individuals and teams on fueling for enhanced performance and making healthy food choices. Currently she writes the nutrition column for UltraRunning magazine and runs ultras herself. She has presented at the National RRCA Convention, the National Rowing Convention, Nike San Francisco Marathon Expo, and the Runners World San Francisco Marathon and worked as an assistant with the Los Angeles Marathon Association. An avid master competitor herself, she trains and competes in the San Francisco Bay Area and beyond. Sunny received her Bachelor of Science degree from University of Southern California and her Masters in Human Nutrition degree from University of New Haven. (Photo at left, by Luis Escobar).