The purpose of this prospective trial was to assess the effect of a VLCD in IBS-D. The results provide preliminary evidence that a VLCD provides adequate relief of IBS-D symptoms, decreases abdominal pain, improves stool frequency and consistency, and improves quality of life. All 13 participants who completed the 6-week study reported adequate relief of their IBS-D symptoms for at least two of the four weeks. More impressively, 10 of these 13 participants reported adequate relief for all four weeks.
This is the first study to assess the effect of a low-carbohydrate diet in individuals with IBS-D, though previous research has investigated the role of carbohydrates in IBS.6, 7
One study of 239 individuals with either IBS or non-specific functional bowel complaints showed an improvement in symptoms after elimination of some combination of sorbitol, lactose, or fructose for one month.6
Additionally, King et al found that individuals with IBS have abnormal colonic fermentation of carbohydrates.7
They found that an exclusion diet that reduced the load of potential offending carbohydrates improved IBS symptoms. However, several studies have shown similarly high rates of abnormal colonic fermentation of carbohydrates in healthy volunteers.18, 19
Also, not all studies have shown benefit when the potential offending carbohydrate is removed from the diet.20
This study has a few limitations. Our study represents the experience of 17 individuals, with 13 participants completing all 6 weeks. The results must be confirmed in larger numbers. Three participants who dropped out did so primarily because of difficulty following a restrictive diet. There is no a priori reason why the drop out group would be different from those who completed the study with regard to treatment benefit. The other main limitation is the lack of a standard control group. Although participants served as their own control for several outcomes, a placebo effect may explain the positive findings, particularly for subjective outcomes such as abdominal pain. However, the use of daily diary cards helps to obviate subjective interpretation or recall bias by providing a systematic and objective measure of daily bowel habits. Finally, most of the participants were women who were overweight or obese, so it is uncertain if these responses would be seen in men or normal-weight individuals.
Despite these limitations, this study found objective evidence that overweight and obese individuals initiating a VLCD had a profound clinical response in their IBS-D symptoms. This finding requires further investigation to identify mechanisms by which a VLCD affects the symptoms of IBS-D. This will elucidate additional dietary and pharmacologic methods for managing patients with IBS-D.