Why Is Sugar Bad for Diarrhea?

Almost everyone enjoys eating something sweet, but few people know that too much sugar can cause a bad case of diarrhea. If you're wondering why your stomach is upset, consider whether you've been chowing down on too many of the wrong sugary foods.

Fructose is one of the sugars most likely to cause a bad case of diarrhea. It's found naturally in ripe fruits such as peaches, pears, cherries and apples, as well as in fruit juices. It is also added to foods in the form of both table sugar and high fructose corn syrup (HFCS).

Harvard Health Publishing estimates that 75 percent of people who ingest more than 40 to 80 grams of fructose per day will get diarrhea. According to the Food and Drug Administration, HFCS is commonly either 42 percent or 55 percent fructose (with the rest being glucose) and sucrose is 50 percent fructose and 50 percent glucose.

With some simple math, you can work out that drinking two 12-ounce cans of sugary soda (containing 38 grams sugar each) provides 41.8 grams of fructose (if they're made using 55 percent fructose HFCS). That's enough to cause diarrhea, if one is susceptible.

Some people will experience diarrhea and bloating more commonly than others, especially after consuming sugar-rich foods. The Cleveland Clinic suggests this is due to person-to-person variation in absorption and gut sensitivity.

If you are prone to symptoms of irritable bowel syndrome (IBS) you may be more likely to experience fructose-related diarrhea than somebody without IBS, according to the Cleveland Clinic. A medical test called a "hydrogen breath test" can check for fructose malabsorption, and also lactose intolerance, according to the University of Michigan. People with both these conditions produce more hydrogen gas (due to the action of bacteria in the gut) than people without them.

Hereditary fructose intolerance is a much more serious inability to process fructose, a condition that affects one in 10,000 to 20,000 people, according to the National Institutes of Health Genetics Home Reference. It usually becomes apparent in infancy, and can lead to growth failure in children.

Read more: Healthy and Unhealthy Foods High in Fructose

Harvard Health Publishing lists certain foods as being potential causes behind any bad case of diarrhea in susceptible individuals. It's worth checking through the list to see if your upset stomach could be caused by any of the following:

• Sweeteners ending "-ol" (e.g. mannitol, sorbitol, xylitol). They are often found in sugar-free mints and gum.
• Dairy foods containing lactose. According to the U.S. National Library of Medicine, about 30 million Americans develop some level of lactose intolerance by the time they are out of their teens.
• Wheat, rye, onions, garlic, pulses, honey, pistachios, cashews, asparagus and artichokes. These are all part of a wider group of fermentable carbohydrates known as FODMAPs that can cause stomach trouble. Lactose, fructose and sorbitol are all part of this group.
• Gluten. Some people who don't have celiac disease may still have trouble digesting gluten.
• Fatty and spicy food. When fatty foods are not absorbed properly, they can cause the bowel to secrete fluid and trigger diarrhea. Spicy food can mask fat content.
• Caffeine. Too much of this stimulant speeds up the digestive system.

Read more: Foods to Eat to Stop Diarrhea