Todo sobre la intolerancia a la fructosa 

Fructose malabsorption or intolerance is very common.

Fructose is absorbed in the small intestine. Even in healthy people, only about 25–50 grams of fructose a day can be properly absorbed. People with fructose malabsorption absorb less than 25 grams a day. 

A protein, called GLUT5, is responsible for transporting fructose in your intestine into the enterocytes, absorptive cells in the gut lining which do the job of absorbing many different nutrients into the blood stream. Fructose malabsorption may be caused by a lack of GLUT5. If extra amounts of fructose are not absorbed and pass into the large intestine, this can cause the uncomfortable symptoms. 

How to know if you are fructose intolerant? The first step is to examine your symptoms, and, making notes in a diet diary, see if there may be a relationship with the consumption of fructose, especially high-fructose products.  

Symptoms of fructose malabsorption may include:  

• Nausea 
• Bloating 
• Flatulence 
• Abdominal pain 
• Diarrhoea 
• Vomiting 
• Chronic fatigue 
• Malabsorption of certain other nutrients such as iron 

These symptoms are shared with several other digestive disorders such as IBS, and also overlap with some of the signs of coeliac disease, an autoimmune disorder that is triggered by eating gluten. If you feel any of these symptoms more than just very occasionally, you should see a doctor.  

Breath testing after ingestion of fructose has been widely adopted as a standard method of identifying fructose malabsorption and intolerance. 

This article is discussing fructose malabsorption, also known as dietary fructose intolerance. It is a very different condition to hereditary fructose intolerance, a rare genetic condition. In hereditary fructose intolerance (HFI), the body does not produce the enzyme called aldobase B, used in the digestion of sugar. In HFI patients, the ingestion of fructose and sucrose causes severe hypoglycaemia (low blood sugar levels) and the build-up of dangerous substances in the liver. The condition is usually detected when babies have this sugar introduced into their diet.   

In terms of the common condition of fructose malabsorption, it is not clear whether the cause can be genetic or hereditary. Among the known risk factors, however, a person who has certain digestive disorders such as IBS, Crohn’s disease, ulcerative colitis and coeliac disease is more likely to develop fructose malabsorption.   

Managing a fructose intolerance or fructose malabsorption requires reducing fructose in your diet. Eliminating all fructose from the diet is extremely difficult, so it is a question of finding the right level for you. A good place to start is by avoiding high-fructose foods such as certain sweetened drinks, cereal bars, fruit juices, honey, processed sweet foods including fructose and some fruits including cherries, prunes, pears, peaches, apples, plums and watermelon.  

Fructose malabsorption may play a role in some people developing IBS. The two conditions often coincide, but more research needs to be done to understand fully what the connection is. One in three adults with IBS is unable to absorb fructose in 25-50 gram intakes. However, fructose malabsorption is not limited to patients with IBS.  

If a person with fructose malabsorption eats plenty of vegetables and fruit low in fructose, there should be no problem getting enough vitamins. However, people with fructose malabsorption have been found to show lower levels of folic acid, and, in some case, zinc. It is important to monitor the levels of these minerals and, if necessary, take action to supplement them.  

Knowing exactly what is in your food is the key to managing any food intolerance, and this means reading and understanding labelling, as well as being proactive and asking about ingredients when consuming products outside your home. With fructose, it is often not the whole foods, such as pieces of fruit, that will catch you out, but rather the added sugar. Remember, fructose is half of the sugar in sucrose, or table sugar. 

When reading through ingredients, look out for high-fructose corn syrup, agave nectar, honey, sorbitol, fructooligosaccharides, corn syrup solids, sugar alcohols, invert sugar, maple-flavoured syrup, molasses and palm or coconut sugar, all of which are high in fructose. 

With coeliac disease, through the damaging of the mucosa, or lining, of the small intestine, a temporary fructose intolerance can develop. This generally disappears once the mucosa has regenerated itself through a gluten-free diet.