What is fructose?

Fructose (= fruit sugar) is a simple sugar (= monosaccharide: mono = 'one', sacchar = 'sweet') that is found in table sugar (= sucrose), fruits, some vegetables, dates and actually all common sugar alternatives, such as honey , agave syrup, coconut blossom sugar, palm sugar, date syrup etc. In contrast to glucose, our body does not depend on fructose. It is harmful to our teeth and organs. In addition, it promotes weight gain, as it is transported to the liver after ingestion, where it is converted into fat (Gameau, 2015, p. 109; Yudkin & Lustig, 2012, p. 29f.).

My blog post 'Sugar Part 2' gives a detailed description what sugar exactly is, how it is processed within the body, why it is so harmful and we should therefore avoid it. 

What is fructose intolerance?

If you are fructose intolerant, only very small amounts or no fructose at all are tolerated. A distinction is therefore made between two forms of congenital and acquired fructose intolerance (Kircher, 2014, p. 17):

The congenital fructose intolerance , also known as hereditary fructose intolerance (= congenital, inherited), is based on an enzyme defect. 'Hereditary fructose intolerance (HFI) is a metabolic disease caused by the absence of an enzyme called aldolase B . In people with HFI, ingestion of fructose (fruit sugar) and sucrose (cane or beet sugar, table sugar) causes severe hypoglycemia (low blood sugar) and the build up of dangerous substances in the liver' (NIH, ２０１５). Meaning: the fructose is absorbed without problems by the intestines, but cannot be converted properly by the liver. Since this form is inherited, the intolerance already occurs in babies who are fed with (poor) baby food containing fructose. The effects are very dangerous and can even lead to coma. Anyone who suffers from congenital fructose-intolerance must not consume any fructose throughout their life. Fortunately, however, this enzyme defect occurs very rarely, with a frequency of 1:20.000 - 1:130.000 - depending on the source (Kircher, ２０１４, p. 2014; Nahrungsmittel-Intoleranz.com, ２０２０).

Within the acquired fructose intolerance, Fructose Malabsorption in the case of Fructose Malabsorption, fructose malabsorption or bacteria , which are producing high concentrations of hydrogen, carbon dioxide and short-chain fatty acids. This leads to bloating, flatulence and abdominal cramps (FETeV, ２０１８; Nahrungsmittel-Intoleranz.com, ２０２０).

Since fructose intolerance is often masked by a concomitant lactose intolerance, it is only possible to estimate how many people are affected by it: it is valued that every third European suffers from fructose malabsorption (FETeV, ２０１８; Food Intolerance Network, ２０１４)!

How can fructose intolerance be tested?

Fructose malabsorption can be tested by a breath test, more precisely a fructose-hydrogen breath test (= H2 breath test). This test is carried out in an allergy clinic, where a concentrated fruit juice solution has to be drunk. After about half an hour you have to blow into a measuring device, which measures the exhaled breath (Kircher, 2014, p. 19). 'The whole test lasts about three hours. When fructose is unabsorbed, it produces higher amounts of hydrogen in the intestines. This test measures how much hydrogen is on your breath from this malabsorption` (Olsen, ２０１８). In order to obtain a valid result, the breath is measured three times at a certain time interval (Kircher, ２０１ ４, p. １ ９). That is why the whole test takes up to three hours.

Symptoms: what symptoms does fructose intolerance cause?

First of all, it must be noted that fructose malabsorption does not run completely the same way in all people. Often, however, those affected suffer from:

• abdominal cramps in the upper abdomen
• diarrhea (constipation can also occur, but this is rarely the case)
• soft defecation
• greasy stools
• bloated abdomen
• strong feeling of fullness
• frequent need to urinate
• headache
• dizziness
• exhaustion
• Depression
• concentration problems
• nervousness
• weight loss

Not all symptoms need to occur at the same time and the intensity can also vary from person to person. Since fructose intolerance is in most cases acquired and not congenital, it is also possible that the complaints get worse over time (Kircher, ２０１ ４, p. ２３). This was the case with me, for example: I have had some of these symptoms for a very long time. Nevertheless, I did not take a test until many years later, namely when the symptoms were almost unbearable. So don't wait too long: knowing how to deal with fructose malabsorption improves your quality of life!

What does the diet look like?

Only a few foods are suitable for a completely fructose-free diet, which should be observed for two weeks:

• Carbohydrates bread, rice (no sugar and no whole wheat products)
• Protein: Eggs, meat, fish, cheese, yogurt (all without sugar)
• some vegetables: all lettuce, chicory, bamboo shoots, swiss chard, mushrooms, radicchio, cucumber, sauerkraut, zucchini, spinach
• Drinks: Water, tea (no fruit teas), milk
• as well as glucose, spelled sugar and rice syrup, if you need some sugar alternatives to sweeten your meals (Kircher, 2014, p. 36).

My doctor gave me the following advice: whole wheat products should still be avoided, as it takes a long time to be digested. The intestines need some time to recover. Vegetables such as broccoli or cabbage, which can bloat, should also be avoided during this special diet.

In addition, make sure that all products (e.g. bread, sausage, etc.) contain no fruit sugar (= fructose) at all (Kircher, 2014, p. 36). In my blog entry "Sugar Part II”I explain exactly what fructose is and where it occurs. Please read the labels of the products you are buying, since sugar is often added to many of these products.

What are the next steps?

After the two-week diet period, a larger selection of foods can be consumed again. Here are a few examples of foods that are usually well tolerated in the case of fructose malabsorption:

Carbohydrates: buckwheat, rice, sugar-free pastries and chickpeas; quinoa, millet and potatoes must be tested to see whether they are tolerated.

Protein: meat, fish, milk products (milk, yoghurt, cheese) without added sugar (no fruit yoghurts), eggs and sausages (without sugar).

Vegetables: lettuce, arugula, chicory, bamboo shoots, swiss chard, parsley, mushrooms, radicchio, cucumber, sauerkraut, zucchini and spinach. After the special diet, also other vegetables can be tried out. Carrots, bell pepper and peas, for example, contain a lot of fructose and should therefore be consumed only in moderation!

Drinks: water, sparkling water (without additives), herbal tea, rooibos tea, black, green and white tea, coffee and milk (Kircher, 2014, p. 47).

Fats: nuts (peanuts contain sorbitol, you have to test whether they can be tolerated) and all kind of oils.

Fruits: Avocado, limes, papaya and lemon are usually well tolerated. The following types of fruit are often tolerated in smaller quantities: apricots, berries (especially blackberries, but also raspberries and blueberries as well as currants and currants), peaches, very ripe bananas, rhubarb, apricots, olives, prickly pears, plums and honeydew melon.

Good to know: the ratio of fructose and glucose is decisive for whether a food is tolerated or not (Kircher, 2014, p. 47ff.). For example, honeydew melon contains more glucose than  fructose . and is therefore usually well tolerated when consumed in small quantities. Also a 1:1 ratio between fructose and glucose, as is the case with very ripe bananas (the riper the banana, the more glucose they contain), is favorable (Nahrungsmittel-Intoleranz.com, 2020). However, it must be individually tested which foods and which quantities can be tolerated (Kircher, 2014, p. 47ff.).