If you have unexplained bloating, gas and IBS symptoms it could be that your body is lacking the enzyme to break down fructose. Found in honey, fruit, fruit juice and some vegetables, fructose is a natural simple sugar that in some people the intestines can’t break down efficiently. This leads to a build-up of fructose in the intestines and results in uncomfortable gut symptoms.
Fructose malabsorption is diagnosed using a hydrogen breath test, which recognises unabsorbed fructose. Not every food that contains fructose is a problem if fructose malabsorption has been identified. It’s a matter of finding out what foods are suitable to eat, and which foods should be limited.
About fructose
The foods we eat are made up of many different components, including sugars. Fructose is a simple sugar or monosaccharide and can be found in many different foods such as honey, agave nectar, wheat, fruit and vegetables. It is also found in high-fructose corn sugar in many processed foods and beverages.
Fruits high in fructose include:
- Apple
- Applesauce
- Dried fruits e.g., raisins, dates
- Fruit juice
- Lychee
- Pears
- Watermelon
- Stone fruits
- Cherries
- Mango
- Nectarines
- Peaches
- Plums
- Prunes
Fruits with a lower fructose content include bananas (unripe), avocado, berries, rockmelon, lemons, pineapple, kiwi fruit and grapes. When fructose is present as a chain of sugar units, it is referred to as a fructan and can cause many of the same digestive problems. Often fructan intolerance and fructose malabsorption can coexist or fructan intolerance can be the underlying cause of symptoms.
Foods that are high in fructans include:
- Wheat products such as bread and pasta
- Barley
- Onions
- Shallots
- Garlic
- Cabbage
- Broccoli
- Artichoke
Symptoms of fructose malabsorption
Fructose intolerance resembles symptoms of irritable bowel syndrome (IBS) and includes nausea, bloating, gas, abdominal pain and vomiting. Usually there is diarrhoea, but this is not always the case and chronic constipation or sluggish bowels can also be a symptom. Fructose intolerance may result in malabsorption of certain minerals such as iron and result in chronic fatigue.
In addition to digestive symptoms, there’s evidence that links fructose malabsorption to mood disorders and depression. Researchers have found that people with fructose malabsorption have lower levels of tryptophan—which is a precursor to our happy hormone serotonin.
Fructose intolerance versus malabsorption
Fructose malabsorption occurs when the human intestine cannot absorb an unlimited amount of fructose, however most people can absorb 25-50 g of fructose per sitting. By definition, inability to absorb 25g of fructose per sitting is considered fructose malabsorption. This is estimated to occur in about one third of the population.
Hereditary fructose intolerance. It occurs when your body is unable to manufacture the enzyme involved in breaking down fructose. This results in toxic symptoms when fructose is ingested. Although fructose is found in fruit, it also naturally occurs in the body, and manmade forms of fructose are frequently used as a sweetener in many foods, including many baby foods and drinks. For enzyme deficient patients, if fructose and/or sucrose is consumed, the body is suddenly unable to convert glycogen into glucose, causing dangerously low sugar levels and toxins to accumulate in the liver. This characteristically leads to chronic fatigue, digestive issues and hypoglycaemia. In rare instances it can lead to more serious complications such as liver failure.
Hereditary fructose intolerance occurs in babies and is usually identified when formula or foods are commenced. If both parents carry an abnormal gene, each of their children has a 25% chance of being affected. The condition may be as common as 1 in 20,000 people in some European countries.
Risk factors
Factors which increase your risk of fructose malabsorption include:
- Small intestinal bacteria overgrowth (SIBO)
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- Imbalance of good and bad bacteria in the gut
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- Overconsumption of fructose
- High intake of refined and processed food
- Gut disorders such as IBS, Crohn’s disease, ulcerative colitis and celiac disease
- Inflammation
- Stress
Diagnosis
Breath test
Your doctor may perform a breath test which measures levels of hydrogen. It involves breath analysis every 30 minutes for 3 hours after drinking a solution that is high in fructose. 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.
Eliminating fructose
Eliminating fructose from your diet is another way to tell if you have fructose malabsorption. With the help of a registered dietitian or nutritionist/naturopath, you can develop a plan to effectively limit any foods containing fructose and see if your symptoms improve. If you have IBS this may be part of a low FODMAP diet which will help to determine a reaction to other fermentable carbohydrates.
Determining your tolerance
Once you have followed these diets for four to six weeks you can start to reintroduce fructose-containing foods back into the diet to determine your threshold. This allows you to still enjoy foods you once ate but only in small amounts so that you are not experiencing any side-effects. However, each case is individual, and some people experience mild symptoms and some very severe. In more severe cases there may be other underlying causes such as other food intolerances/allergies and SIBO.
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Short and sweet
In short, fructose malabsorption is a common enzyme deficiency that is prevalent in the general population but particularly in those with IBS and SIBO. It leads to uncomfortable digestive symptoms such as abdominal pain, bloating, nausea, vomiting and diarrhoea/constipation. The condition can be diagnosed via a breath test and managed by limiting fructose-containing foods.
References
https://www.healthline.com/health/fructose-malabsorption
https://ghr.nlm.nih.gov/condition/hereditary-fructose-intolerance
Putkonen L, et al. Fructose malabsorption syndrome. Curr Opin Clin Nutr Metab Care. 2013 Jul;16(4):473-7 https://www.ncbi.nlm.nih.gov/pubmed/23739630
Fedewa A, et al. Dietary fructose intolerance, fructan intolerance and FODMAPs. Curr Gastroenterol Rep. 2014 Jan;16(1):370. https://www.ncbi.nlm.nih.gov/pubmed/24357350
Ledochowski M, et al. Fructose malabsorption is associated with decreased plasma tryptophan. Scand J Gastroenterol. 2001 Apr;36(4):367-71 https://www.ncbi.nlm.nih.gov/pubmed/11336160
Gibson PR, et al. Review article: fructose malabsorption and the bigger picture. Aliment Pharmacol Ther. 2007 Feb 15;25(4):349-63 https://www.ncbi.nlm.nih.gov/pubmed/17217453
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