Fructose intolerance: which foods contain it and how much you can tolerate

What is fructose and where does the fructose you eat come from?

Fructose is a simple sugar. It occurs naturally in fruit, honey and many vegetables [2].

It is also found in ordinary table sugar. Sucrose consists of equal parts glucose and fructose [2]. The intestine separates them before absorbing them.

The third source is the high-fructose corn syrup found in many industrial products, with 42-55 % fructose [2]. You will not see it listed separately on the label, because the “sugars” line in the nutrition information adds up all the monosaccharides and disaccharides in the food [3]. The clue is in the ingredients list.

Table of foods with no or little fructose

This fructose table lists ranges per 100 g of edible portion. It comes from the table by Zugasti Murillo, adapted from Olveira Fuster’s Manual de nutrición clínica y dietética [1].

Group	Very low (less than 1 g)	Low (1-3 g)	Medium (3-5 g)	High (more than 5 g)
Fruit	Avocado, lime, coconut, tiger nuts, apricot, papaya	Plums, redcurrants, mandarin, orange, peach, melon, nectarine, grapefruit, pineapple, watermelon	Blueberries, strawberry, raspberry, large strawberry, pomegranate, guava, currants, mango, kiwi, dried peach, quince, blackberries, banana. Orange and pineapple juice	Dried apricot, persimmons, cherries, sour cherries, prunes, custard apple, dates, dried figs, fresh figs, apple, pear, plum, grapes
Nuts	Almonds, hazelnuts, chestnuts, pine nuts, peanuts	—	—	—
Vegetables and legumes	Artichokes, chard, garlic, sweet potato, aubergine, watercress, mushrooms, spinach, peas, broad beans, chickpeas, lettuce, lentils, potato, cucumber, mushrooms, corn, radish, beetroot	Celery, broccoli, pumpkin, onions, cabbages, cabbage, cauliflower, endive, carrot, asparagus, leeks, tomato	—	—
Starchy foods	Cereals and bread products	—	—	—
Dairy	Milk, condensed milk, cheese, curd cheese	—	—	—
Protein	Eggs, unprocessed meat and fish	—	—	—
Other	Margarine, chicory, custard, flan	—	—	Royal jelly, honey, jam, sugary drinks, sweetened or honey-coated cereals, fruit in syrup, chocolate, quince paste, alcohol

The table provides guidance on fructose, but it does not determine your tolerance. Plum appears in two ranges in the original, and those cells need review.

Do tomatoes, onions or carrots contain fructose?

Yes, but only a little. All three are in the low range, between 1 and 3 g per 100 g [1]. Celery, broccoli, pumpkin, cauliflower, leek and asparagus are in this range too.

Among the fruits people ask about most, melon and watermelon are in the low range [1]. Banana, mango and kiwi are in the medium range; apple, pear and grapes are in the high range. Avocado, cucumber, garlic, potato, rice and bread are in the lowest range of all.

What is the difference between fructose malabsorption and fructose intolerance?

The European breath-test guideline distinguishes malabsorption from intolerance [4]. Malabsorption means that some fructose reaches the colon without being absorbed. Intolerance means that symptoms occur after consuming it. A positive test alone does not explain every symptom.

Absorption capacity varies between people and according to the amount consumed [4]. Other fermentable sugars in the same food may also affect symptoms. Monash University distinguishes fructose from sorbitol, fructans and legume oligosaccharides [5].

What is not absorbed draws in water and is fermented by bacteria in the colon. This causes gas, bloating and diarrhoea. It is the same mechanism behind abdominal bloating, and explains why so many people with irritable bowel syndrome report the same issue with fruit.

What is hereditary fructose intolerance?

Hereditary fructose intolerance is a different disease. A change in the ALDOB gene is inherited from each parent. It affects approximately one in 20,000 people [2].

It usually becomes apparent when foods containing fructose are introduced during childhood [2]. Diagnosis and follow-up by a specialist metabolic diseases unit are needed.

Vomiting is the constant finding; hypoglycaemia, a drop in blood sugar, is less common. Nausea, sweating, lethargy, dehydration, abdominal pain, an enlarged liver, jaundice and impaired growth may also occur [2].

Sometimes diagnosis comes late because the child starts rejecting sweet foods to protect themselves, which happens after the vomiting [2]. Today it is confirmed with a genetic test of the aldolase B gene. The old fructose-loading test is reserved for exceptional cases because of the risk of acute liver failure [2].

The dietary plan for this disease avoids fructose, sucrose and sorbitol for life [2]. The specialist unit reviews foods and medicines, including their excipients. It also assesses whether the diet meets vitamin C requirements [2].

The optimal degree of restriction has not yet been established [2], and the amount is set by the specialist metabolic unit managing the case. If you have received this diagnosis, that unit is your point of reference.

How is a low-fructose plan followed in phases?

If your doctor has ruled out other causes and the link with your symptoms has been documented, we use a temporary reduction in the amounts that cause you discomfort [4].

You then reintroduce foods one at a time and observe your response. The maintenance phase keeps the widest variety you can tolerate. Here we adapt the three phases described by Monash University for the low-FODMAP diet [6].

This plan addresses digestive symptoms related to fructose. Hereditary fructose intolerance requires specialist follow-up and a different restriction [2].

How much fructose can you tolerate?

There is no universal threshold for fructose. The European guideline explains that the minimum amount tolerated by most people has not been measured systematically [4]. Tolerance can also vary with portion size and other components of the meal.

In a Monash University trial, adding glucose improved the absorption of dissolved fructose according to breath hydrogen [7]. When added to foods, it improved neither that measure nor symptoms [7]. That is why adding sugar to fruit is not a way to relieve symptoms.

How can you tell whether you are fructose intolerant?

Your doctor assesses your symptoms and, when appropriate, requests a breath hydrogen test. The European guideline proposes 20-25 g of fructose for adults [4]. If there are warning signs, these are investigated first [4].

A positive result indicates malabsorption with the dose used in the test. To find out whether it explains your symptoms, a record is kept of what you eat and when symptoms occur [4].

The European guideline recommends eliminating foods only when this link has been documented [4]. In children, the test has limitations and its usefulness is still debated [4].

What mistakes do we see in appointments?

There are three stumbling blocks we hear about almost every week in appointments, and all three prolong the problem.

Cutting out all fruit at once. It is the first reaction and the least helpful one. With the table in front of you, there is almost always some fruit you can eat, and the amount can be adjusted gradually.

Switching to juice or “sugar-free” products. Orange juice is in a higher range than a whole orange [1]. And a “sugar-free” product sweetened with sorbitol also provides fructose, because the body can convert sorbitol into fructose [2].

Trusting an IgG, hair or bioresonance test. None of these can diagnose fructose intolerance, and our team does not consider such a result reliable.

If sorbitol also causes you problems

Fructose and sorbitol are both FODMAPs, carbohydrates that can cause digestive symptoms. Fructose belongs to the monosaccharides and sorbitol to the polyols, according to Monash University [5].

A table that measures fructose alone does not provide information about sorbitol. If several foods bother you, it is a good idea to review both with your dietitian.

If you suspect both, read the guide to sorbitol, with its own food-by-food table. If irritable bowel syndrome is behind it, the relevant tool is the low-FODMAP diet. It is followed with guidance and in phases, with 2 to 6 weeks of strict restriction followed by gradual reintroduction [6].