Patients with irritable bowel syndrome and fructose malabsorption appeared to benefit from a diet that restricted intake of fructose and fructans, Susan J. Shepherd and her colleagues reported in an article appearing in the July 2008 issue of Clinical Gastroenterology and Hepatology.
In the 25-patient study, the diet led to “marked and sustained global improvement in gastrointestinal symptoms,” researchers noted. A subsequent study of the patients revealed that symptom relief was not specific to restricted intake of fructose, but was achieved by limiting the intake of poorly absorbed short-chain carbohydrates.
These findings “represent the first high-level evidence” that poorly absorbed short-chain carbohydrates—fructose and fructans—are dietary triggers for the symptoms of irritable bowel syndrome (IBS) in patients who also have fructose malabsorption.
The results also demonstrate that restricting intake of these substances may lead to durable symptomatic improvement, wrote Ms. Shepherd, a dietician at Australia's Monash University, Clayton, Victoria, and her colleagues.
They theorized that, because many abdominal symptoms may originate from bowel distension, addressing factors that contribute to the distension would improve symptoms. In the current study, the researchers focused on osmotic load within the lumen and fermentative gas content.
Poorly absorbed short-chain carbohydrates, including fructose and lactose, are highly fermentable. They exert a strong osmotic effect in people who have malabsorption of these two sugars—about 40% of the population in the case of fructose, and between 15% to 100% of the population for lactose.
To minimize or eliminate intake of poorly absorbed short-chain carbohydrates, the investigators created a diet that omitted fruits containing more fructose than glucose, such as apples, pears, and watermelon; vegetables containing fructan, such as onions, leeks, asparagus, and artichokes; wheat products that contain fructan, such as breads and pasta; foods that contain sorbitol, such as stone fruits; and foods that contain raffinose, such as legumes, lentils, cabbage, and brussels sprouts.
In addition, the diet omitted foods that contain lactose in diets for patients who also had lactose malabsorption.
The study group consisted of 21 women and 4 men aged 22–63 years who had had IBS for a median of 9 years, as well as fructose malabsorption. They adopted this rigorous diet for 3–36 months. Their food was provided for them, with a daily energy content of 8, 10, or 12 mJ/day, according to their individual needs. Patients were also given a list of alternative foods they could substitute while dining out.
All of the patients on the diet achieved sustained improvement in their GI symptoms, the investigators said.
The subjects then were challenged in a double-blind crossover fashion with four orange-flavored test drinks that were identical in appearance, prepared by mixing either fructose, fructans, fructose plus fructans, or glucose powders with 500 mL of water. The glucose drink served as a placebo, since glucose is rapidly and completely absorbed.
The subjects were instructed to drink these three times a day for 2 weeks, starting at a low dose (50 mL per meal) and increasing to a high dose (170 mL per meal).
All IBS symptoms were significantly more frequent and more severe after ingestion of the fructose, fructans, and combined fructose-fructans drinks than with the glucose drink. In contrast, non-IBS symptoms such as tiredness did not differ between the treatment and glucose groups.
The IBS symptoms became more intense as the doses of the fructose, fructans, and combined fructose-fructans drinks increased, but there were no such changes with increasing doses of the glucose drink. The fructose-fructans combination caused more severe symptoms than fructose alone.
The results show that restricting intake of fructose and fructans may lead to durable improvement of GI symptoms, and that poorly absorbed short-chain carbohydrates in general, rather than free fructose specifically, are an important trigger of IBS symptoms, wrote the authors.
Ms. Shepherd disclosed that she has published cookbooks concerning fructose malabsorption and celiac disease.