Fructose is a form of sugar (carbohydrate) commonly found in fruits and vegetables. How these sugars are processed in the body determines their potential effect. Some people cannot metabolise fructose appropriately and they ferment at a rapid rate causing digestive symptoms – thus indicating their intolerance.
All of the foods we eat are made up of many components – carbohydrates, proteins and lipids. Fructose is present in a single sugar form and also as a chain of fructose sugar units (fructans).
Fructose intolerance is either hereditary (rare autosomal disorder) or conditional (i.e. developed later on in life). Recent research indicates that fructose intolerance affects greater than 30% of the population.
Contributing factors include:
- Diabetes (especially type 2)
- Metformin (type 2 diabetes medication)
- Diets that are high GI (glycaemic index)
- Corticosteroid usage
- Digestive damage from excessive alcohol, smoking and other factors
As you can see from the above list, fructose intolerance is likely to occur from poor blood sugar regulation and digestive damage – commonly seen in inflammatory bowel disorders such as Crohn’s disease and ulcerative colitis. Additionally, conditions such as IBS (irritable bowel syndrome) can be misdiagnosed. It is worth checking all possibilities with your health professional.
Normally, fructose is absorbed in the small bowel. In fructose malabsorption, the normal absorption of fructose is impaired. Fructose malabsorption can cause symptoms including:
- Stomach bloating
- Stomach pain
- Change in bowel habits – loose bowel motions, diarrhoea and/or constipation
These are common symptoms that can be diagnosed as irritable bowel syndrome (IBS). Please remember that IBS is a diagnosis of exclusion and often all options are not sufficiently excluded.
Fructose malabsorption is also associated with gastro-oesophageal reflux, SIBO (small intestinal bacterial overgrowth) and depression.
Fructose malabsorption can be diagnosed using a hydrogen breath test, which recognises unabsorbed fructose. If fructose is not absorbed in the small intestine it reaches the distal end of the small intestine and the colon where it is fermented by colonic flora to produce H2 and CO2. Fructose is fermented especially quickly, therefore there is not enough time for gas to be further metabolised or absorbed, increasing intra-lumen pressure and producing an osmotic effect. Abdominal distension, pain, flatulence and diarrhoea may result.
The FODMAP diet
Dr Sue Shepherd developed a form of fructose malabsorption diet. Subsequently a team at Monash University, led by Professor Peter Gibson and including Dr Shepherd and others, developed the low FODMAP diet.
They have proven, through their pioneering research, that limiting dietary FODMAPs is an effective treatment for people with symptoms of IBS.
FODMAPs are found in the following foods (1) :
- Oligosaccharides (eg. Fructans and Galactans)?
- Disaccharides (eg. Lactose)
- Monosaccharides (eg. excess Fructose)?
- Polyols (eg. Sorbitol, Mannitol, Maltitol, Xylitol and Isomalt)
Fructose malabsorption diet
The glucose/fructose ratio is important when designing a low fructose diet. If the amount of fructose is higher than that of glucose, exacerbations can ensue.
Foods that contain fructose in higher or equal amounts to glucose include (1) :
- Excess Fructose: Honey, Apples, Mango, Pear, Watermelon, High Fructose Corn Syrup, Corn Syrup Solids
- Fructans: Artichokes (Globe), Artichokes(Jerusalem), Asparagus, Beetroot, Chicory, Dandelion leaves, Garlic (in large amounts), Leek, Onion (brown, white, Spanish, onion powder), Raddicio lettuce, Spring Onion (white part), Wheat (in large amounts), Rye (in large amounts), Inulin, Fructo-oligosaccharides.
- Lactose: Milk, icecream, custard, dairy desserts, condensed and evaporated milk, milk powder, yoghurt, margarine, soft unripened cheeses (eg. ricotta, cottage, cream, marscarpone).
- Galacto-Oligosaccharides (GOS): Legume beans (eg. baked beans, kidney beans, bortolotti beans), Lentils, Chickpeas
- Polyols: Apples, Apricots, Avocado, Cherries, Longon, Lychee, Nectarines, Pears , Plums, Prunes, Mushrooms, Sorbitol (420), mannitol (421), xylitol (967), maltitol (965) and Isomalt (953).
Fructose malabsorption is a complicated dietary condition and it is crucial that you are properly assessed and directed by a health care practitioner. If you think that any of the symptoms or health aspects listed above sound familiar, then please make an appointment to see a Naturopath, GP or Dietician for thorough assessment and management.
Further research and reading
- Dr Sue Shepherd