Fructose Intolerance: Types, Symptoms, and Diet

What is fructose intolerance? What diet should I follow for the fructose intolerance diet? Today, we will provide you with all the information you need to know about this pathology that increasingly affects a higher percentage of the population.

What is fructose?

Fructose is a type of simple sugar found in fruits and honey. It is also a component of table sugar (sucrose) along with glucose. Some vegetables also contain fructans, which are chains of fructose.

Another sugar related to fructose is sorbitol, commonly used as an additive and sweetener in many processed foods.

 

Difference between intolerance and malabsorption

Before discussing fructose intolerance, it is crucial to differentiate between intolerance and malabsorption, as they are not the same thing. Understanding the mechanisms of fructose absorption is key to this differentiation.

Fructose is absorbed in the small intestine by a specific transporter called GLUT 5. This transporter carries fructose from the small intestine to the bloodstream, where it is then metabolized in the liver. Another transporter, GLUT 2, is responsible for transporting sugars such as glucose or galactose.

The presence of sorbitol can decrease fructose absorption because it appears that they share the same transporter (GLUT 5). This is why sorbitol is also restricted on a low fructose diet for individuals with fructose intolerance.

Malabsorption occurs due to the absence of the specific transporter (GLUT 5). However, when symptoms associated with malabsorption are present, we refer to it as intolerance. This occurs because the unabsorbed fructose reaches the colon, where it comes into contact with bacteria and ferments, releasing gases.

Fructose and sorbitol malabsorption

Sorbitol malabsorption is also produced by the absence of the same specific transporter, GLUT 5. It is important to note that even if there is no absence of the transporter, a person can absorb a limited amount of sorbitol, specifically about 20-25 grams approximately. In other words, if this amount is exceeded, the symptoms of sorbitol malabsorption can occur, whether or not there is an absence of the transporter.

As for fructose malabsorption, it is important to know that it is not a simple mechanism, as there are fructose-intolerant people who can still consume sucrose (glucose + fructose). This happens because fructose needs another non-specific transporter (GLUT 2) that shares with other sugars such as glucose. In the case of fructose + sorbitol, the absorption is very difficult, as both are competitors for the same transporter.

We also call malabsorption secondary fructose intolerance.

Types of fructose intolerance

There are two types of fructose intolerance:

• Primary or hereditary fructose intolerance: There is a deficiency or absence of the aldolase B enzyme, genetically mediated, so it is hereditary. It is less common. Fructose consumption is limited for life; it is evaluated with a genetic study.

• Secondary fructose intolerance or malabsorption: This is more frequent and evaluated with a breath test. As its name indicates, it is secondary to another pathology, usually related to the presence of intestinal diseases such as:

  • Inflammatory bowel disease
  • Irritable bowel syndrome
  • Gastroenteritis
  • Celiac disease
  • Bacterial overgrowth

If the intestinal disease is cured, the intolerance usually also disappears.

Symptoms of fructose intolerance

If there is fructose intolerance or malabsorption, some of the following symptoms may occur:

• Flatulence and gas
• Abdominal distension
• Diarrhea (explosive)
• Intestinal noises, vomiting, and/or nausea
• Stomach cramps
• Abdominal pain
• Constipation
• Weakness

Long-term fructose intolerance can also cause deficiencies in micronutrients, changes in the gut microbiome, or increased intestinal permeability.

Diet for fructose intolerance

When planning a diet for someone with fructose intolerance, we must keep in mind that both the degree of malabsorption and the degree of intolerance are not the same for all patients; it will vary depending on the patient's transporter deficit and intestinal sensitivity. So it is very important to individualize and customize the dietary guidelines.

Some people with limited fructose absorption capacity may have intolerance symptoms produced by unabsorbed fructose that reaches the colon. In this case, the objective is to limit the intake of foods rich in fructose to a level that does not cause symptoms, according to individual tolerance. Partial restriction is sufficient, maintaining these foods in the diet in tolerable quantities to avoid the risk of nutritional deficiencies.

The capacity to absorb fructose improves with the simultaneous intake of glucose, which generally means good tolerance to sucrose or common sugar. On the other hand, sorbitol present in some foods naturally or as an additive (E-420) increases the risk of symptoms.

Related: The 10 Foods That Lower Blood Sugar Level

Recommendations for improving fructose intolerance

Recommendations to Improve Fructose and Sorbitol Tolerance:

• The best-tolerated fruits have low fructose content and include:

  • Oranges, tangerines, bananas, lemons, avocados, kiwis, blackberries, strawberries, blueberries, raspberries, grapefruit, grapes, and melons.

• Eating foods with fructose in small amounts spaced out throughout the day.

  • Limit yourself to one fruit serving or equivalent at a time, with a maximum of 2-3 servings per day.

• The best-tolerated vegetables are:

  • Broccoli, chard, spinach, celery, artichokes, watercress, tapioca, mushrooms, lettuce, endive, and chicory. Older potatoes contain lower fructose levels than new potatoes.

• Cooking vegetables reduces fructose (it is lost in the cooking liquid, which should be discarded), making them easier to tolerate.

• Limit your intake of foods with fructose content higher than glucose content and foods containing mixtures of fructose and sorbitol. These include some fruits (apples, pears, plums, cherries, peaches, apricots, etc.), commercial fruit juices, and some sweets (chewing gum, candies, sweets, etc.).

• Foods of animal origin (meat, fish, eggs, etc.) can be safely consumed if they are not processed. Fructose and sorbitol may be added during processing.

• In general, it is best to avoid commercial fruit drinks (juices and soda) and all products sweetened with fructose and sorbitol. Many medications in syrup form contain glucose or sorbitol. Although the amount consumed is typically small and does not usually cause symptoms, consulting with a doctor for possible alternatives is recommended.