Gels and Stomach Distress

Written by Bruce R. Copeland on December 23, 2008

Tags: caffeine, carbohydrate, energy gel, fructose, nutrition, stomach distress, ultrarunning

There have been quite a few posts on different trail and ultrarunning blogs about people getting upset stomachs from gels (see e.g. I truly believe some runners CANNOT tolerate prolonged gel consumption. However, before you conclude that you’re one of those people, let’s make certain something else isn’t the problem. [Some of what follows can also be found in the special topics article “Biochemical Strategies for Ultramarathon Running” as part of a broader discussion of carbohydrate and fat calorie needs for running.]

Long distance running is inherently stressful to the stomach. Very small tears occur in the stomach and intestinal lining. This is not dangerous, but it does significantly upset the stomach. Moreover heavy exercise diverts blood from the stomach to the muscles, thereby decreasing the digestive and nutrient uptake activity that the stomach can support. Race stress further affects the stomach. Your stomach may be unhappy regardless what you eat! If you are running a sub-20 hour pace for a 100 mile race, you are pushing the limits of human aerobic energy metabolism. I really applaud you, but it is fairly certain you will encounter stomach problems.

There is an established upper limit to how much carbohydrate a runner can consume per hour before their stomach shuts down. For a 150 lb runner, that limit is 100-130 grams (about 350 calories or a little over 3 gels). If you weigh less or more than 150 lb, scale that number down or up accordingly. A few elite ultrarunners may be able to get away with consuming 3 gels per hour, but most of us mere mortals are much safer with 2 gels per hour. OK, when I say 2 gels per hour I mean 2 gels per hour—I do NOT mean zero gels one hour and 4 gels the next. Even at 2 gels per hour, you can still find yourself in trouble if you consume a sports drink or eat large amounts of other food. Sports drinks contain upwards of 50 grams carbohydrate per liter (quart).

Carbohydrate also needs to be consumed with sufficient water so that the carbohydrate concentration in the stomach doesn’t exceed 100-120 grams per liter. You need to drink at least 8 ounces of water per gel!

If you experience stomach problems from gels and aren’t consuming too concentrated or too much carbohydrate, there may still be a few other things to check. Fructose is a major component in many gels. A certain amount of fructose is beneficial for many endurance athletes, but some people do not tolerate fructose well. If you think you might be one of them, then try Clif products—these contain no significant fructose. Many gels contain electrolytes, but athletes vary substantially in their need for and tolerance of certain electrolytes. You might want to test gels that contain lesser amounts of sodium. I am a big fan of caffeine for distance running, but too much caffeine is also hard on the stomach. Make sure you aren’t experiencing stomach distress from too much caffeine in your gels.

Hope this helps!!!