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In super-duper layman’s terms, an upset stomach occurs when you have solid food or fluids in your gastrointestinal system that are not processed properly. So why is this such a common issue when fueling with energy gels?

During a race, three integral systems – muscles, digestion, and cooling – constantly fight for your blood. 

  • That’s why your legs feel especially heavy after a big meal (digestion requires more resources to process the food, meaning less for your muscles). 
  • That’s why it’s harder to maintain pace on hot summer days (more blood is needed for cooling). 
  • That’s why your stomach often rebels when physically pushing yourself to the limit (blood is diverted from the stomach to maintain muscle functions).

When exercising, your stomach isn’t at an optimum state to begin with, and now you ingest dose after dose of sweet syrupy energy gels… I’m amazed that gastrointestinal distress doesn’t happen more often.

Before we get into the causes of upset stomach and prevention tips, let’s better understand the digestive system.

What is the digestive system?

The digestive system consists of the gastrointestinal tract (mouth, esophagus, stomach, small intestine, large intestine, and anus), liver, pancreas, and gallbladder. Digestion helps you process food and drinks to extract and absorb nutrients the human body needs. Each organ of the digestive system moves food and fluids through the gastrointestinal tract, processes food and drinks into absorbable components, or distributes nutrients to various parts of the body.

For example, proteins are broken down into amino acids, fats into fatty acids, and carbohydrates into sugar.


Exercise compromises digestion

As mentioned, your digestive system is not operating optimally when you’re running or cycling, especially not at hard race efforts because when you’re moving, blood is diverted from the digestive system to fuel your muscles.

Food and drinks that usually go down smoothly now may cause gastrointestinal distress. To make matters worse, energy gels, with their high sugar concentration, are not something you eat daily.

Energy gels require extra hydration

Energy gels are essentially highly concentrated sugar water, which require water to break down. If you don’t drink enough fluids with energy gels, your body will draw water from the digestive tract to assist digestion, further compromising the entire system. 

Stomach pain, dehydration, and inflammation are some common side effects. However, over drinking can also be problematic because it lowers your body’s electrolyte concentration. Not to mention how uncomfortable it is to run with a stomach full of water sloshing around. 

It just doesn’t taste good

I’m in the camp of “there are no tasty energy gels, only tolerable ones.” The digestive tract begins with the mouth, meaning your taste buds are part of the equation. Energy gels can be sickeningly sweet and come in thick syrupy pastes. Not a winning, delicious combination.

Consuming packages of gel one after another may cause sweetness fatigue – you simply can’t imagine yourself eating another one. And if you don’t select options that agree with your taste buds, nausea and even vomiting are not uncommon.


The gassy runner

Not all carbohydrates we eat are processed in the small intestine. Some continue down to the large intestine, producing short-chain fatty acids and gas, which benefit gut bacteria. This is all part of a healthy digestive system. 

However, during training and a race, we consume a large amount of carbohydrates in the form of energy gels. When they’re not processed, it produces excess gas and may cause stomach bloating, leading to stomach cramps and diarrhea. Fructose, an ingredient in many sports fuels, is often the culprit of gas buildup in the large intestine.


Mental block

For those who had terrible experiences with energy gels in the past, the horrific memory stays with them for a long time (like that one bad tequila night ruining tequila for you forever). I know runners who can’t stomach even a tiny bit of energy gels. Just the smell can set them off.


5 tips to overcome stomach issues

Here is a list of dos and don’ts for consuming energy gels. And here’s a complete guide for daily, race-day, and recovery fueling. Have a read for more in-depth information.

  1. Practice, practice, and practice. You can train your gut just like you train your legs, heart, and lungs. Don’t try anything new on race day you haven’t practiced using.
  2. Know your body. How much energy gels do you need, and how much can you tolerate? Here’s a good starting point. Consume 1g of carbohydrate per kg of body weight per hour. A 60kg athlete should take in 60g of carbohydrates each hour, about 2-3 energy gels. Know your body and personalize.
  3. Have a plan for hydration. A typical gel is 30g and provides 20g of carbohydrates and 100 calories. The rule of thumb is every 20-25g of carbohydrates require 250 ml of water to process. Not drinking enough fluids causes upset stomach, dehydration, or sweetness fatigue.
  4. If you have a sensitive stomach, try taking a smaller amount more regularly. For example, the average marathoner swallows an entire energy gel every 20-30 minutes. You can try slowly consuming the energy gel over a 5-10-minute period. Remember to select energy gels with suitable packaging for this fueling strategy to avoid making a mess. Sticky hands are annoying.
  5. If energy gels are just not for you, there are other alternatives, such as honey, maple syrup, sports drinks, fruit, and energy bars. Once again, practice, research, and personalize your fueling.