Intolerance of fructose (fructose intolerance or more precisely, fructose malabsorption) is the most common of all food intolerances.
Estimates suggest that nearly one in three Europeans suffer from this condition, which often occurs in combination with lactose intolerance. Fructose intolerance must be strictly distinguished from the hereditary intolerance, which is a serious metabolic disorder and usually appears during childhood (a genetic test can be performed for the determination of this disorder).
How does fructose intolerance develop?
The small intestine contains certain transporters for fructose. These transporters are called GLUT and SGLT and transport fructose from the digested food through the intestinal wall into our blood. GLUT is the abbreviation of glucose transporter and SGLT is the abbreviation from the term "sodium-glucose linked transporter", a sodium-dependent glucose transporter. The number and/or function of these transporters can be reduced/impaired resulting in poor absorption of fructose, which then passes into the large intestine. Bacteria in the large intestine are able to ferment fructose (as well other FODMAPs) and this can lead to bloating and other symptoms. Overall, the exact cause of intolerance is not yet fully understood.
What are the symptoms associated with fructose intolerance?
The usual symptoms of fructose intolerance are diarrhoea, abdominal cramps, bloating, nausea or fatigue. There are certainly more symptoms that range through to depression (see below).
How can I determine whether I suffer from fructose intolerance?
Fructose intolerance is diagnosed using the hydrogen (H2) breath test we perform in our practice. After determination of the fasting value (fructose), levels of hydrogen in the exhaled air are measured at various time intervals after ingestion of 25 g fructose.
How can I treat fructose intolerance?
It makes sense to reduce the amount of dietary fructose. However, complete elimination of fructose is not useful as this may even lead to a worsening of the disease; fructose elimination can reduce the transporter even further when fructose is completely missing from one’s diet. It is also sensible to include dietary fructose in combination with glucose as this promotes the increase of specific GLUT transporters in the intestinal wall, which aids in better absorption of fructose ("glucose trick").
In an initial phase, one should avoid fructose (and sugar alcohols) as much as possible. Thereafter, you can experiment by eating small amounts until you have reached the "dose" you can tolerate, and stick with this determined amount. These fructose amounts change over time, so you can always experiment to find your optimal “dose”.
Sorbitol should be avoided because it is suspected to inhibit fructose uptake by inhibiting the GLUT-5 transporter (see also sorbitol intolerance).
Fructose is better tolerated by many patients in the afternoon perhaps because by the afternoon, more fructose transporters are functioning in the intestine.
During treatment and adjustment to a fructose-low diet, we recommend working closely in conjunction with nutritional counselling.
Where is fructose found?
Generally little or no fructose is found in cereals, rice, potatoes, dairy products, meat, poultry, fish, mineral water (without sweetener!), coffee, and tea.
In fruits and vegetables, chickpeas, peas, potatoes, spinach, chard (mangold), radishes, Chinese cabbage, cauliflower, lettuce, cucumber, prickly pears (from cactus), avocado, rhubarb among others low in fructose.
Nuts are (excluding peanuts which contain sorbitol) also well tolerated.
High fructose, mannitol or sorbitol can be found in almost all fruits (e.g. apples, plums, pears etc.), all dried fruits, fruit juices, soft drinks, honey, wine, and cider. In recent years, the food industry has added more and more fructose-containing sweeteners to many different products (especially processed foods).
We can certainly organize nutritional advice for you.
Can fructose cause depression?
There is evidence that the intake of fructose in the presence of fructose intolerance can lead to depression in some people. The theory is that tryptophan (an amino acid that must be absorbed from food and is converted to serotonin [the so-called "happiness hormone"]) becomes bound in a strong complex with fructose in the intestine. Therefore, with high fructose concentrations and fructose intolerance, tryptophan cannot be taken up by the body. A lack of serotonin can lead to a depressive mood or depression. In conjunction with a low fructose diet, such symptoms may completely disappear. Nevertheless, there are many other reasons for the presence of depression.
There is evidence that other foods can govern our well-being.
Source: Ledochowski M, Widner B, H Bair, Probst T, Fuchs D. Fructose and sorbitol-reduced diet improves mood and gastrointestinal disturbances in fructose malabsorbers. Scand J Gastroenterol 2000; 35(10):1048-1052.