Fructose malabsorption

Jennifer Butt discovers that avoiding fructose is no way as easy as it sounds...

When my partner Bernhard was diagnosed with fructose malabsorption (FM) shortly before Christmas, my initial reaction was ‘at least it’s better than lactose intolerance. It must be fairly easy to avoid fruit sugar, mustn’t it?’

How wrong could I be?

Fructose malabsorption is often referred to as fructose intolerance but the two are different. Hereditary fructose intolerance is a serious disease. FM is unpleasant but not life-threatening. It is caused by the inability of the small intestine to break down fructose. The sugar passes undigested into the large intestine where it is broken down into short chain fatty acids and gases (carbon dioxide, hydrogen and methane). These gases create pressure in the intestine resulting in bloating, cramps, diarrhoea and flatulence. FM can also lead to anaemia and depression.


FM is diagnosed by a test similar to that for lactose intolerance. Bernhard drank a fructose solution provided by the doctor and measured the hydrogen levels in his breath for the next two hours. The results showed he was noticeably malabsorbant. However different people have different tolerance levels. Some people react to very small amounts of fructose whereas others can consume large amounts without noticing. It is thought that a third of the population has FM but of these, a third to a half show no symptoms. This implies that up to 1 in 6 of us suffer a reaction to fructose, usually without knowing the cause.


According to Martin Baker, vice-president of Metabolic Solutions Inc, an American producer of FM breath tests, ‘the extent of fructose malabsorption in the general population and the consequences of the condition are unknown. Chronic fatigue symptom and irritable bowel syndrome have been associated with fructose malabsorption but there have been no robust scientific studies to confirm this relationship. As a result, the hydrogen breath test for fructose malabsorption is used infrequently.’


Once diagnosed, Bernhard set out to adjust to his new way of life. But it has not been easy. For one thing, avoiding fructose is not as simple as just avoiding fruit. You have to stay away from fruit and all other products that are both high in fructose and relatively high in fructose compared to glucose. For complicated reasons, which go over my head, the presence of glucose helps fructose to be digested.

Unfortunately FM often goes hand in hand with a sweet tooth. Luckily my partner can tolerate a small amount of fructose so judiciously chosen sweets are allowed. But how should he select from the sweets on offer in a restaurant?

On the menu are pears in chocolate sauce, cheesecake with raspberry coulis, chocolate fudge cake and tiramisu. Which of these will have the least evil consequences? It’s easy to dismiss the pear dish – pears are among the worst offenders and unfortunately Bernhard has a lovely pear tree in his garden. But how does he know how much fructose is in the other desserts?

Assessing the content

A lot of manufacturers use high fructose syrup and are not obliged to put this on the label. It is cheaper than sugar and is increasingly used, particularly in soft drinks and baked goods.

As well as fructose he would like to know the glucose content of the puddings on offer. If there is more glucose than fructose the dish will be easier to digest (within reason – I’m afraid that nothing will put apples back on his menu). It is not always obvious.

For instance, I assumed that brown sugar was worse for him than white, because it tastes so strong. But I found a 20-year-old list of products on the internet which shows that brown sugar has a high proportion of glucose. So we think brown sugar sandwiches are okay - he certainly enjoys them. But I’m not entirely sure and his stomach hasn’t yet given a definitive answer.

Lack of information

The other big problem is a lack of consistent information. My partner lives in Germany and although the breath test was covered by his health insurance the dietitian was not. He has found two books on the subject, both by the same author and neither particularly helpful. For instance there is no information about carrots or green beans. There is nothing about the fructose content of ordinary cooking ingredients like sugar, flour or cocoa powder.

I checked with the British Library. They hold 22 million items – surely a few will be about FM? Unfortunately not. They hold no books at all on FM and list only 10 articles published in medical journals – each of which would cost £26-30 to read. One out-of-print book pops up on Amazon but I’m not even sure it’s on the right subject. Various websites exist, seemingly from reputable sources. Most are not detailed enough to be helpful, or else they contradict each other.

Bananas are good – no they’re not, bananas are evil! Wheat is not dangerous – eat wheat at your peril! Besides, how do we consult a website when we’re in a restaurant looking at the sweet menu?

It can be difficult to explain FM. A few weeks ago some friends conscientiously offered us rhubarb – they thought because it was sour it would be low in fructose. Bernhard had a homemade cheese straw for pudding instead.


Ironically, FM sufferers have to avoid diabetic or ‘sugar-free’ products - sorbitol or other sugar substitutes can aggravate the condition. And there are so many other things to avoid, not just fruit or sweets.

...and vegetables

Lots of vegetables are on the banned list - tomatoes, sweet peppers, artichokes, cabbage and even parsley. How can you have pizza without the tomato sauce?

The last six months have been a period of trial and error – and frustration as we’ve realised how little information is available. Bernhard misses eating apples, jam and honey the most. He certainly doesn’t miss the diarrhoea and the bloating. Fortunately he loves dark chocolate - the good quality stuff tends to be low in sugar. He eats a lot of cucumber (which according to some is evil stuff) and so far is okay with it. He would choose cheesecake in my hypothetical restaurant above, but ask for cream instead of the raspberry coulis.

Would he trade fructose malabsorption for lactose intolerance? Like a shot!

USDA - Sugar content of selected foods
American Journal of Gastoenterology - Dietary Fructose and Gastrointestinal Symptoms
The Food Intolerance Institute of Australia - fructose intolerance

First published in 2007


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