April 15, 2024
An upset stomach with diarrhea and gas often makes people think of irritable bowel syndrome (IBS) or lactose intolerance. However, the issues could just as likely be due to poor absorption of fruit sugar—fructose, and this condition is called fructose malabsorption.
Malabsorption means that the intestines struggle to absorb certain nutrients. Fructose is not fully absorbed in the small intestine in any human. So, it can be said that everyone malabsorbs fructose to some extent. Instead of being absorbed in the small intestine, fructose moves to the large intestine where gut bacteria feast on it. For those with sensitive intestines, this can cause gas, diarrhea, and general stomach discomfort.
As many as one-third of Sweden’s population is affected by fructose malabsorption to varying degrees. Fructose is also a FODMAP molecule, meaning that one can react to small amounts of fructose without having fructose malabsorption.
There are tests to check for fructose malabsorption. These are breath tests and are not widely used in Swedish healthcare. The simplest way is to experiment by consuming foods high in fructose and observe how the stomach reacts. Foods with excess fructose include fruit juices, apples, and pears.
Fructose malabsorption is likely a congenital, genetic condition, and the cause can be found at the molecular level. Fructose is absorbed in the small intestine with the help of glucose. As long as there is a 50-50 balance of glucose and fructose, everything works smoothly. However, if what you eat contains more than 50% fructose, problems arise when the glucose runs out. The main sources of fructose are, of course, various types of fruit, but it is also found in other foods, such as regular white sugar. What’s interesting in this context is the ratio between fructose and glucose (dextrose).
A natural question in this context is whether you can add extra glucose to increase the absorption of fructose. For example, assume you’re eating a fruit salad. By choosing fruits with a lower fructose content (such as banana, orange, kiwi) and at the same time consuming something that contains glucose, the absorption of fructose can be improved. However, this works better in theory than in practice, but for those who are sensitive, it might be a good idea not to eat fruit on an empty stomach, but rather after a meal.
Sofia Antonsson
Reg. Dietitian, Belly Balance
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