One of the most common food intolerances is that of fruit sugar - fructose. In some countries, such as Germany, one in three people is affected. There may be a congenital intolerance, in which even with a small amount there are digestive problems. But usually most people have a problem with too much fructose. Many foods today are sweetened with fruit sugar instead of regular sugar , which contributes to the fact that there is much more fructose in the diet than is useful. 
The problem is that many products add fructose such as ketchup, fruit milk, canned food and more. We have plenty of fruit all year round from the tropics, greenhouses and dried fruits. Most likely, the intolerance is due to the fact that the body needs to readjust to a new diet. 
People with congenital fructose intolerance have fewer enzymes to process it. If intolerance occurs later in life, it is assumed that there is a problem with the intake of fructose in the intestine and fewer transport channels in the intestinal wall. From a small amount of fruit sugar, the transport channels are overloaded and the sugar passes to the intestinal microflora in the colon and leads to unpleasant symptoms. 
Fructose intolerance can also affect mood. During digestion, the amino acid tryptophan attaches to fructose. If there is too much fructose that we cannot absorb, we will lose tryptophan. From the amino acid tryptophan is formed serotonin, the so-called hormone of happiness. Lack of serotonin can lead to depression, so a long-established fructose intolerance can lead to depressed mood. 
Serotonin, in  addition to our good mood, is also responsible for the feeling of satiety. If we often experience a loud voice and eat constantly, this may be due to fructose intolerance, as well as if we have complaints such as diarrhea and abdominal pain. 
How much fructose is good for us? From more than 50 grams of fracture per day (5-8 fruits) the transport systems are overloaded. With a larger amount, there may be diarrhea, abdominal pain and gas. Today we consume three to four times more fructose than the generations before us. 
Fructose-glucose syrup is used in many products in the store, such as pastries and salad dressings, as well as in fast food restaurants. It suppresses satiety signals such as leptin and makes us eat more. 
Although fruits are useful, it is good to rethink the amount we take. More and more people have food intolerances, and most of them are more sensitive to a particular food than genetic intolerance. This means that they will be able to deal with small amounts of irritating food. 
Even if there is no established intolerance to certain foods, if the exclusion of a food has a good effect on the body, it is good to comply with this. Sensitivity to certain foods can be caused by antibiotic treatment, stress, gastrointestinal infections and overeating. This does not mean that we should completely avoid foods to which we are sensitive , but it is good to take such an amount that our body can handle.