Restricting dietary fructose, fructans may improve IBS.
In the 25-patient study, the diet led to "marked and sustained global improvement in gastrointestinal symptoms," investigators reported.
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 in general.
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 the investigators, led by Ms. Shepherd, a dietician at Australia's Monash University, Clayton, Victoria.
The researchers theorized that, because many abdominal symptoms may originate from bowel distension, addressing factors that contribute to the distension would improve symptoms. Two such factors that Ms. Shepherd and her associates focused on were 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--approximately 40% of the population in the case of fructose, and anywhere from 15% to 100% of the population for lactose, the investigators wrote.
Other poorly absorbed short-chain carbuhyilnites considered good targets for intervention were polyols such as sorbitol, which are generally poorly absorbed; and fructans (fructo-oligosaccharides) and galacto-oligosaccharides such as raffinose. for which humans do not express suitable hydrolases.
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 25 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 per day for 2 weeks, starting at a low dose (50 mL, per meal) and working up 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.
Moreover, 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 drink caused more severe symptoms than did fructose alone.
One-third of the subjects were unable to progress to the high-dose drinks because their symptoms escalated severely as doses increased.
The results show that restricting intake of fructose and fructans may lead to durable improvement of GI symptoms, Ms. Shepherd and her associates said.
The findings also suggest that poorly absorbed short-chain carbohydrates in general, rather than free fructose specifically, are an important trigger of IBS symptoms, they added.
Ms. Shepherd disclosed that she has published cookbooks concerning fructose malabsorption and celiac disease.
BY MARY ANN MOON
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|Title Annotation:||Clinical Rounds|
|Author:||Moon, Mary Ann|
|Publication:||OB GYN News|
|Date:||Jul 1, 2008|
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