FRUCTOSE MALABSORPTION AND ITS SYMPTOMS
Fructose malabsorption is the insufficient uptake of fructose from the small intestine. A daily load greater than 25mg is often too much to absorb for affected individuals. Unabsorbed fructose travels to the bowel where it causes numerous side effects. As a substrate for microbial fermentation, it produces gases (e.g. hydrogen and methane) which cause flatulence and bloating. Other effects include osmotic diarrhoea, abdominal pain and dysbiosis. The shift in microbial colonies further influences gut motility and contributes to local inflammation and increased permeability of the gastrointestinal wall. Reflux is also linked to fructose malabsorption in many patients.
HOW TO DIAGNOSE FRUCTOSE MALABSORPTION
Identifying fructose malabsorption requires a process of elimination.
- Rule out serious conditions such as coeliac disease, inflammatory bowel diseases and colorectal cancer. The presence of blood in the stool, significant weight and anaemia must be taken seriously and rigorously investigated (e.g. colonoscopy)
- Consider other carbohydrate intolerances known to cause similar symptoms e.g. lactose intolerance.
NB: Many who suffer with severe IBS present with multiple intolerances and malabsorption issues, and require additional relevant treatments.
- Symptom resolution achieved by removing high-fructose and other problem foods (table 1) from the diet is highly suggestive of fructose malabsorption. Confirmation can be obtained through the breath hydrogen test (BHT). The BHT is performed after a fructose challenge and measures the amount of hydrogen released by intestinal microbial fermentation of fructose in the bowel. Hydrogen exceeding 20 points above baseline indicates fructose malabsorption.
HOW TO MANAGE FRUCTOSE MALABSORPTION AND ITS SYMPTOMS
A low fructose diet remains the most effective method of symptom management. The scientific community has also been investigating other practices that may improve patient outcomes.
Complete avoidance of fructose is not necessary as small doses are still well tolerated. Fructose consumption should be limited to less than 25mg daily. Foods that are very high in fructose (see table 1) are best avoided. Restrict consumption of fruit juices, dried fruit, and products sweetened with apple, pear or high fructose corn syrup (HFCS). HFCS is not used widely in Australian foods, but is common in imported products. Glucose appears to stimulate GLUT5 and hence improve fructose uptake. Therefore, foods that contain more glucose than fructose are generally well tolerated (e.g. ripe bananas).
Sorbitol intake should be restricted to less than 5g per day, whether it be naturally sourced (e.g. prunes) or a food additive. Sorbitol reduces fructose uptake, and worsens symptoms by contributing to osmotic diarrhoea. High concentrations of fructans often pose a problem. Fructans are present in many wheat products, which may explain why many IBS sufferers respond well to a wheat-free diet despite testing negative for coeliac disease.
Once symptoms have subsided, patients may wish to reintroduce small portions of prohibited foods to determine their tolerance level. Due to glucose’s ability to upregulate GLUT5, glucose powder added to fruit juices/drinks or high fructose foods whilst cooking, may improve fructose absorption. This is recommended only occasionally.
FOODS TO AVOID
Artichokes, asparagus, beetroot, broccoli, brussel sprouts, cabbage, fennel, garlic, lebanese cucumber, leek, radicchio lettuce, onion, peas and sugar snap peas, spring onion.
Apple, guava, mango, nashi, pear, persimmon, rambutan, watermelon, fruit juice /concentrate /cordial, soft drink, dried fruit, tinned fruit.
Wheat, honey, corn syrup, coconut cream/milk, tomato sauce/paste, chutney, relish, bbq/plum/sweet & sour sauce, agave syrup, sorbitol.
FOODS YOU CAN EAT
Alfalfa, avocado, bamboo shoots, bean shoots, bok choy, capsicum, carrot, cauliflower, celery, choy sum, corn, green/continental cucumber, eggplant, green beans, lettuce (butter, endive, iceberg), mushrooms, olives, parsnip, pumpkin, silverbeet, snowpeas, spinach, squash, swede, sweet potato, tomato, turnip, water chestnut, white potato, zucchini.
Apricot, banana, blueberry, blackberry, boysenberry, cantaloupe, cherry, coconut flesh/fibre, cranberry, cumquat, fig,, grapefruit, *green grapes, honeydew melon, kiwi fruit, lemon, lime, lychee, mandarin, nectarine, orange, passionfruit, pawpaw, peach, pineapple, plum, quince, raspberry, rhubarb, star fruit, strawberry, tangelo, tamarillo.
Red meat, chicken, turkey, fish, dairy foods, eggs, white rice, legumes (ie.chickpeas, lentils), soy, tamari soy sauce, nuts, seeds, herbs, spices, molasses, rice syrup, maple syrup, golden syrup, and asafoetida (An indian herb used as an onion alternative)
ADDED EXTRAS ON FRUCTOSE
1.Coconut oil and coconut flesh are tolerated by those with fructose malabsorption. However coconut milk or cream have a higher fructose content and therefor not tolerated well.
2. Fennel seed is not listed as having high fructose and yet the fennel as the vegetables does have a high fructose and is best avoided.
3. *Green grapes are okay in very limited amounts. Purple grapes have too high a fructose load, so are best avoided.
4. Lebanese Cucumbers have a high fructose concentration but green and continental cucumbers are tolerated
5. Every individual may have different degrees of sensitivity. The fructose is generally only a problem when a food contains more fructose than glucose.. This is why some fruit, such as kiwi, is tolerated, as the fructose amount is in complete balance with the amount of glucose. Therefore, the amount of the 'other' sugar needs to be greater than the amount of fructose eaten in the one meal for fructose absorption to be improved. Glucose and dextrose can improve fructose absorption only if the amount is greater than the amount of fructose consumed. Sucrose is broken down during digestion into equal amounts of glucose and fructose, and may be tolerated in small amounts. However, large amounts of sucrose will release too high a total load of fructose
MOOD AND FRUCTOSE MALABSORPTION…A MISSING LINK?
Research has demonstrated that a fructose and sorbitol reduced diet in subjects with fructose malabsorption not only reduces gastrointestinal symptoms but also improves mood and early signs of depression. Further investigations identified that fructose malabsorption is associated with lower tryptophan levels, which may play a role in the development of depressive disorders. High intestinal fructose concentration seems to interfere with L-tryptophan metabolism, reducing its availability for serotonin syntheses. In patients reporting concurrent mood disorders and IBS symptoms, fructose malabsorption should be considered. An adjusted diet, together with probiotic and essential fatty acid therapy is likely to remarkably improve their quality of life.