Fructose intolerance

5. August 2021

What to watch out for

What to watch out for

Many people suffer from food intolerances which cause significant symptoms and make everyday life more complicated. Lactose, fructose, and histamine intolerance are common, and often cause discomfort. Let’s take a look at the consequences of fructose intolerance.

The most common form of intestinal fructose intolerance affecting the gut is fructose malabsorption. You can be born with this condition or acquire it later in life. The cause of fructose intolerance is a defective transport protein called the GLUT-5 transporter.

Around 30% of the German population suffer from fructose intolerance. Things aren’t any better at a European level either. Around 30-40% of Central Europeans are affected by fructose malabsorption, with around half of this number suffering from symptoms.

Around 20 to 30% of the European population cannot digest all sugars such as fructose, sorbitol or lactose. For this reason, the A149P, A174D and N334K mutations are most common in Europe. These are responsible for about 85% of all patients with HFI (hereditary fructose intolerance).

HFI is inherited as an autosomal recessive trait. This means that you will inherit the condition if both of your parents are carriers of this genetic deviation. Statistically speaking, your risk of developing the condition is 25%. The sad thing is that it cannot be treated with drugs. Treatment basically consists of eliminating fructose from your diet. 

Wikipedia says: hereditary fructose intolerance (HFI) is a rare disease caused by a hereditary disorder of the fructose metabolism, whereby the body is unable or insufficiently able to break down the fructose-phosphate 1 formed from fructose (fruit sugar). As a result, the cell’s fructose content increases with toxic effect, which in turn disrupts the body’s metabolism of glucose and causes hypoglycaemia. HFI should not be confused with the much more common intestinal fructose intolerance due to fructose malabsorption.

In other words: there are two different forms of fructose intolerance. Intestinal fructose intolerance (fructose malabsorption) is an acquired condition, whereas hereditary fructose intolerance is a rarer congenital metabolic condition. Anyone who suffers from HFI will have to avoid fructose for the rest of their lives.

Diagnosis: fructose intolerance 

It’s not easy to arrive at a diagnosis of fructose intolerance. People often suffer symptoms for years and go through a marathon of doctor’s appointments before receiving the correct diagnosis. This is because complaints such as abdominal pain, cramps and indigestion are not always correctly attributed by doctors. Often, patients receive other diagnoses before fructose malabsorption is established as the cause of their problems. What happens in the body of those affected:

When you suffer from fructose intolerance, fructose from your intestine is not properly absorbed into your blood, with the result that your body is unable to absorb sufficient quantities of fructose.

In your large intestine, the fructose is broken down by bacteria into hydrogen, methane, carbon dioxide and short-chain fatty acids, which gives rise to symptoms.

Symptoms and complaints

Typical symptoms of fructose intolerance include flatulence, diarrhoea, constipation, headaches, bloated stomach, nausea, abdominal pain and cramps. In the case of advanced fructose intolerance, further symptoms can include a weak immune system, depressive moods, food cravings and listlessness.

As you can see, many factors come together here to make your life more difficult. If you suspect that you may be suffering from fructose intolerance, your doctor can easily clarify this with the help of a breath test: the so-called H2 hydrogen breath test will determine whether you are correct.

The fructose stress test is very accurate and informative. If this test confirms your suspicions, you have to be prepared to radically change your eating habits if you want to avoid potentially life-threatening conditions. If acquired fructose intolerance remains undetected for a long time, you may suffer from deficiency symptoms and your intestinal flora may be damaged.

However, if you are suffering from the hereditary form of fructose intolerance, the hydrogen breath test is not without risk, since it involves the ingestion of a highly concentrated fructose solution. If you suffer from HFI, this could trigger hypoglycaemic shock, which could cause you to lose consciousness. The symptoms of hereditary fructose intolerance include vomiting, hypoglycaemia (low blood sugar), enlargement of the liver with later transition to cirrhosis, coagulation disorder, shock and protein excretion via the kidneys (proteinuria). 

There’s only one thing for it:

If you suffer from hereditary fructose intolerance (HFI), your only option is to avoid foods containing fructose for life, and that is easier said than done. Fructose is mainly found in fruit and honey, but also in vegetables. Grapes, fresh dates, redcurrants and dried fruit have a particularly high fructose content. 

Prohibited foods if you have hereditary fructose intolerance

The Institute for Nutritional Information has compiled a list of prohibited foods that sufferers of HFI cannot consume. This list includes table sugar, honey, invert sugar, diabetic sugar, all foods containing sugar such as any kind of sweets, sweetened milk and cereal products, sweetened sausage products, and tinned fruit and vegetables. It also includes all not expressly permitted types of fruit and vegetables, fruit juices, jams, (ready-made) mayonnaise, ketchup, ready-made sauces, meat, cured meat and fish with ready-made salad dressings or marinades. And that’s not all – it also covers all foods containing insulin such as Jerusalem artichokes, all foods made with sorbitol (check ingredients: sorbitol has an E number and is displayed as E420). Caution is also advised with pills and tablets.

Treatment of hereditary fructose intolerance

If you have HFI, the only way to avoid liver disease is through a strict avoidance of fructose for life. This form of fructose intolerance therefore requires a completely different diet than if you suffer from intestinal fructose intolerance (fructose malabsorption). Don’t forget: this condition cannot be treated with drugs. In the case of fructose malabsorption (acquired fructose intolerance), the situation is different. Acquired fructose intolerance can be brought under control and sometimes the symptoms even completely cured. But you should know that unfortunately it’s not that easy, as it takes years of discipline and a lot of patience. 

You don’t have to renounce everything, thankfully, because luckily there are also low-fructose vegetables that you can eat in bulk. These include mushrooms, chicory, broccoli, lamb’s lettuce, green beans, lettuce, radishes, white cabbage, tomatoes, cauliflower, Chinese cabbage, kale, peas, mushrooms, radishes, asparagus, cucumber, spinach, celery, Swiss chard, carrots, sauerkraut and courgettes. When it comes to fruit, you need to look very closely at the nutritional values.


SUGAR CONTENT OF FRUIT: TABLE OF FRUIT VARIETIES – sugar content per 100 g

Pineapple 3.1 g
Apple 11.4 g
Apricot 8.5 g
Banana 21.4 g
Pear 2.4 g
Blackberry 2.7 g
Strawberry 5.5 g
Fig 12.9 g
Pomegranate 16.7 g
Grapefruit 8.9 g
Blueberry 7.4 g
Raspberry 4.8 g
Redcurrant 7.3 g
Blackcurrant 10,3 g
Kiwi 10.8 g
Mandarin 10.1 g
Mango 12.8 g
Maracuya 13.4 g
Mirabelle plum 14.0 g

Nectarine 12.4 g
Orange 9.2 g
Papaya 2.4 g
Peach 8.9 g
Plum 10.2 g
Sour cherry 11.0 g
Gooseberry 8.5 g
Sweet cherry 13.3 g
Watermelon 8.3 g
Grape 15.6 g
Damson 8.8 g

As you can see, it makes a big difference whether you eat a pear or a banana (data source: University of Hohenheim, Institute for Biological Chemistry and Nutritional Sciences).

Watch out for babies and toddlers

We’re particularly concerned about congenital fructose intolerance in babies and small children. Babies are simply not able to articulate in order to communicate their symptoms, so parents need to pay special attention to how their babies behave after being fed. Babies show intolerance reactions when their diet switches to baby food. Baby food is everything that babies ingest except breast milk or infant formula, for example fruit, vegetables, potatoes, etc.

How can you tell if your baby is fructose intolerant? If you notice that your baby or toddler refuses sweet foods, is reluctant to eat them, or suffers from vomiting, shakes, flatulence, nausea, cramps, diarrhoea or constipation after eating them, you must see your paediatrician immediately, otherwise serious developmental disorders can occur. Early diagnosis is the only way to prevent the condition from worsening.

If you suffer from HFI, there is only one thing you can do: avoid fructose.

Stay healthy!

Sources:

Institute for Nutritional Information