Digestive Disorders > Intolerances > Fructose Intolerance

The symptoms of fructose intolerance

Dr. med. Andre Sommer

Dr. med. Andre Sommer

Fructose intolerance can have a major impact on the body and mind. It is therefore important to recognize the intolerance at an early stage. The symptoms often seem rather unspecific at first. So misdiagnosis can quickly occur. The symptoms that indicate fructose intolerance are discussed below.

What is fructose intolerance?

Fructose is known colloquially as fruit sugar. With an intolerance, this type of sugar is** not properly absorbed by the intestine. Fructose intolerance is therefore also called fructose malabsorption. The fructose molecules remain in the colon and are **broken down there by bacteria. This promotes the emergence of gases and short chain fatty acids, which produce the typical symptoms of food intolerance such as bloating and gut pain.

When does fructose intolerance occur?

Basically anyone can experience fructose intolerance. Our body has only a certain number the Transporter (GLUT-5 transporter), which carries the fructose from the intestine into the blood carry, So only a limited amount of fructose can be absorbed.

If this threshold is exceeded the fructose remains in the intestine. There fermentation processes occur due to bacteria. The development of symptoms depends on the amount of fructose that cannot be absorbed. Which part of the intestine this happens in and how many bacteria are there also plays a role. Ultimately, one speaks of a fructose malabsorption if symptoms appear.

When do symptoms of fructose intolerance appear?

Since malabsorption and thus a reaction occur immediately after eating fructose-containing foods, the typical symptoms usually appear between 30 and 90 minutes after the meal. However, delayed reactions can occur up to 24 hours after admission. In this case, special attention must be paid, as this can make the diagnosis more difficult.

Symptoms also differ from person to person. It can happen that you can easily eat fructose on one day and be plagued by symptoms the next.

What are the symptoms of fructose intolerance?

Short-term symptoms can include the following:

  • Flatulence (sometimes with corresponding, mostly unpleasant smelling intestinal gases)
  • Nausea
  • Bloating
  • Vomiting
  • mushy stool to diarrhea
  • Constipation
  • Abdominal pain and / or cramps

Furthermore, the following diffuse symptoms can occur:

  • Headache
  • Reflux
  • Fatigue
  • Tiredness
  • Sleep problems
  • Dizziness


What diseases can occur in connection with fructose intolerance?

There are some symptoms and diseases that occur together with fructose malabsorption.


Long-term consequences do not occur in everyone. You can prevent this by going to the doctor early and getting treatment. It is particularly useful to change your diet, as this not only causes symptoms but can also treat the causes.

Below are some of the diseases and symptoms that can be associated with fructose intolerance.

Mood swings to depression

Some studies have shown that women with fructose intolerance have more depression symptoms than healthy people. The tryptophan metabolism, **which may be disturbed with fructose intolerance, seems to play an important role here. This molecule is necessary for producing thehormone serotonin**. Seratonin is important for mood regulation. If the body lacks it, you can become depressed. The first signs of depression can be:

  • Listlessness
  • Fatigue
  • Difficulty concentrating
  • Mood swings
  • Exhaustion

If such symptoms occur, it is important to describe them to the attending doctor in connection with the other symptoms. They could be a serious indicator for the diagnosis.

Decreased intake of important nutrients

Fructose malabsorption decomposes the fructose of intestinal bacteria. So it can happen that the number and type of bacteria change. The balance of the intestinal flora is disturbed and otherwise easily digestible substances can suddenly no longer be absorbed through the intestine. This can lead to a deficiency.

Small intestine colonization (SIBO - small intestinal bacterial overgrowth)

The intestine consists of two sections, the small intestine and the large intestine. The bacteria that appear in the two sections differ. There are usually fewer bacteria in the small intestine. Fructose malabsorption can cause bacteria from the large intestine find their way into the small intestine and colonize it. This can have very uncomfortable consequences, causing a lack of nutrients, abdominal pain and bloating.

Non-alcoholic fatty liver disease (NAFLD; also NASH: non-alcoholic steatosis hepatis)

This disease is also caused by increased blood lipid levels. Triglycerides, a specific form of blood lipids, play a role here. The fatty acids that result from bacterial decomposition from fructose are incorporated into triglycerides. The fat is stored in the liver and damages it.


Bad breath is caused by the decomposition of fructose in the intestine and the resulting gas. Good oral hygiene helps fight the symptom but does not attack the cause.

How is the diagnosis of a fructose intolerance made?

With the suspicion of fructose intolerance, it is very important to report the medical history and the associated symptoms in detail to the doctor. If there is suspicion of a fructose intolerance, you will receive a hydrogen breath test (H2breath test). If bacteria in the intestine decompose the fructose and this creates gases, these can be detected with the hydrogen breath test. The diagnosis becomes clear when there is an improvement in symptoms after an applied therapy and the associated change in diet.

How is fructose intolerance treated?

To treat the entirety of the symptoms, the cause has to be addressed. Only dietary changes can help here. It is important that fructose is not permanently removed from the menu, as this in turn can have other negative consequences. Instead, the diet can be adjusted to the amount of fructose that the body can still digest normally. At the same time, those affected should also take into account other intolerances and diseases that can appear together with fructose intolerance. Recently there are tablets on the market that can be taken before a meal containing fructose. However, the study situation is still very limited. For this reason, the classic approach of changing your diet is recommended.

Gibson PR, Newnham E, Barrett JS, Shepherd SJ, Muir JG. Review article: fructose malabsorption and the bigger picture. _Aliment Pharmacol Ther. _2007;25(4):349-363

Komericki P, Akkilic-Materna M, Strimitzer T, Weyermair K, Hammer HF, Aberer W. Oral xylose isomerase decreases breath hydrogen excretion and improves gastrointestinal symptoms in fructose malabsorption - a double-blind, placebo-controlled study. _Aliment Pharmacol Ther. _2012;36(10):980-987.

Ledochowski M, Widner B, Sperner-Unterweger B, Propst T, Vogel W, Fuchs D. Carbohydrate malabsorption syndromes and early signs of mental depression in females. _Dig Dis Sci. _2000;45(7):1255-1259.

Dr. med. Andre Sommer

Dr. med. Andre Sommer

I’m André, a medical doctor from Berlin. Together with a team of medical doctors, nutritionists and data scientists we empower people to understand digestive issues with our app Cara Care.

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