High Amount of Dietary Fiber Not Harmful But Favorable for Crohn Disease

Dietary fiber is known to 1) improve laxation by increasing bulk and reducing transit time of feces through the bowel; 2) increase excretion of bile acid, estrogen, and fecal procarcinogens and carcinogens by binding to them; 3) lower serum cholesterol; 4) slow glucose absorption and improve insulin sensitivity; 5) lower blood pressure; 6) promote weight loss; 7) inhibit lipid peroxidation; and 8) provide anti-inflammatory properties (Figure 1).⁴ After a large prospective cohort study, Park et al⁴ found that dietary fiber intake was significantly inversely associated with risk of total death and death from cardiovascular disease, infectious diseases, and respiratory diseases in both men and women. Dietary fiber intake was also related to a lower risk of death from cancer in men (Figure 1). Among specific sources of dietary fiber, fiber from grains showed the most consistent inverse association with risk of total and cause-specific death. Namely, current chronic diseases are related to decreased consumption of dietary fiber—which is a part of dietary Westernization.⁵ In evaluating the effects of dietary Westernization we are apt to stress adverse effects of increased consumption of animal protein or animal fat, but it is equally important to stress the drawbacks of decreased consumption of dietary fiber.

Our understanding of the mechanisms of the effect of dietary fiber has advanced since Burkitt et al,⁶ on the basis of epidemiologic data, postulated that the high incidence of colon cancer, diverticulosis, irritable bowel syndrome, and hemorrhoids as well as atherosclerosis, coronary artery disease, diabetes, obesity, and hyperlipidemia is secondary to prolonged fiber deprivation.⁷ Indigestible dietary fiber is metabolized to short-chain fatty acids, primarily acetate, propionate, and butyrate, by gut bacteria.⁸ Short-chain fatty acids serve as a major energy source for colonocytes. Among short-chain fatty acids, butyrate has a critical role in colonic homeostasis owing to a variety of functions: inhibiting inflammation and carcinogenesis, reinforcing various components of the colonic defense barrier, decreasing oxidative stress, and providing a satiety sensation.⁸ These beneficial effects overlap naturally with those of dietary fiber (Figure 1). Therefore, it is reasonable to postulate a sequence of shortage of dietary fiber, decreased butyrate, and loss of homeostasis that leads to chronic diseases (Figure 1). Recent observations that gut microflora is formed by diet⁹ and an introduction of the concept that gut microflora is an environmental factor in obesity studies underline the critical role of diet.¹⁰ A supporting example of the intestinal metabolism of dietary phosphatidylcholine and cardiovascular risk was recently published.¹¹

Faecalibacterium prausnitzii is one of the most abundant commensal bacteria in the human intestinal microflora of healthy adults, representing more than 5% of the total bacterial population. F prausnitzii is known to produce butyrate, and its production is associated with dietary fiber.¹² A meta-analysis shows that the fecal bacterial count of F prausnitzii in patients with inflammatory bowel disease (IBD) is significantly lower than in healthy controls, particularly in CD (Figure 1).¹³ Whether this finding is observed even before treatment for IBD or whether it is a secondary effect of the current low-residue diet in IBD is to be elucidated.

Three studies described by Hou et al¹⁴ on pre-illness dietary fiber consumption and CD showed that high fiber intake decreased CD risk. One study showed statistical significance in those consuming more than 22.1 g/day compared with less than 13.8 g/day (odds ratio, 0.12; 95% confidence interval, 0.04–0.37).

The cohort study by Ananthakrishnan et al,¹ in which 170,776 women in the Nurses’ Health Study were followed up for 26 years, found that the highest quintile for consuming dietary fiber (median, 24.0 g/day) was associated with a 40% reduction in risk of CD compared with the lowest quintile (11.6 g/day) (Table 1). This was the first prospective cohort study on a large scale determining the relationship between dietary fiber and the risk of CD. It was concluded that long-term intake of dietary fiber is associated with a lower risk of CD.

There have been two dietary intervention studies in CD focusing on dietary fiber. Heaton et al¹⁵ reported significant efficacy of an unrefined-carbohydrate, fiber-rich diet in CD compared with a control diet in the number of hospital admissions, the duration of hospitalizations, and total number of days in the hospital. In this study, dietary fiber was 33.4 ± 1.8 g/day (Table 1). However, a controlled multicenter trial by Ritchie et al¹⁶ in 1987 was not able to reproduce the effect (Table 1). To our knowledge, there has been no subsequent intervention study focusing on dietary fiber. The above conflicting results seem to be because of the difference in subjects that happened while evaluating the maintenance effect of a concomitant elemental diet during infliximab therapy.¹⁷ The early use of infliximab is more effective than late use in CD, which seemed to result in the conflicting effects of an elemental diet. Most patients (69%) were newly diagnosed (within 3 months) in the study by Heaton et al,¹⁵ whereas most patients (54%) were long-standing with intestinal resection in the study by Ritchie et al.¹⁶ Recently diagnosed cases might be more responsive to dietary manipulation than long-standing cases.

Expanding our knowledge in gut microflora led to the concept that the greatest environmental factor in IBD is diet-associated gut microflora.¹⁰ The microflora is disrupted in IBD mainly by a Westernized diet: increased consumption of animal fat, animal protein, and sugar as well as decreased consumption of dietary fiber. The conventional recommended diet for IBD is a low-residue diet that stems from a fear of irritating the bowel with dietary fiber. However, there is no evidence that such a diet is ideal for IBD.¹⁸ A low-residue diet that lacks nondigestible carbohydrates might accelerate the dysbiosis in IBD.^19,20 Hoping to increase beneficial bacteria in the gut, we initiated a semivegetarian diet (SVD) replacing the low-residue diet.¹⁸ Our SVD is a lacto-ovo-vegetarian diet with an additional serving of fish once a week and meat once every 2 weeks. We provided SVD during hospitalization for 22 consecutive adult CD cases: 14 men and 8 women, age 19 to 77 years (median, 26.5 years), with enterocolitis (11), enteritis (1), or colitis (10). Seventeen patients had active CD whereas 5 patients had undergone resective surgery immediately before the intervention. With regard to the active CD patients, 12 were experiencing the initial onset and 5 were experiencing relapse, the median disease duration was 8.0 months (range, 1 to 74 months), and the main medication was standard induction therapy with infliximab in 16 patients and sulfasalazine in 1. SVD was initiated on the same day as infusion of infliximab. With regard to the postoperative CD patients, 1 was experiencing initial onset with 2 years of disease duration and 4 were experiencing relapse with disease duration more than 8 years; the intervention began on postoperative day 12 to 25; and the main medication was metronidazole 750 mg/day. Initially approximately 800 or 1100 kcal/day was given, and calories were gradually increased to a maximum of approximately 30 kcal/kg standard body weight. The median length of SVD was 49 days for those with active CD and approximately 3 weeks for those with postoperative CD. Remission was defined as the disappearance of active symptoms of CD. All active CD patients obtained remission: the CD active index significantly decreased from 255 ± 169 (mean ± SD) on admission to 46 ± 24 at week 6 (p < 0.0001).

Those patients who achieved clinical remission, either medically or surgically, were provided dietary guidance for SVD before discharge and were advised to maintain SVD after discharge. None of the patients took infliximab or immunosuppressants in the follow-up study. Our SVD contains 32.4 ± 2.1 g of dietary fiber (soluble dietary fiber, 6.8 ± 0.7 g; insoluble dietary fiber, 23.3 ± 1.6 g) in 2000 kcal. The amount is far in excess of the recommended amount for the Japanese population, 17 g/day for women and 20 g/day for men (Table 1).

Each patient’s dietary pattern was assessed by means of a food-frequency questionnaire. When the following 2 conditions were fulfilled, it was regarded as SVD. One is that a patient follows the principle of SVD: daily intake of rice, vegetables, and fruits, and occasional intake of fish, meat, and other animal-based foods. The other is that a patient refrains from foods reported as risk factors for IBD in or outside Japan. A diet that did not fulfill these 2 conditions was regarded as an omnivorous diet. Compliance to SVD was 100% among inpatients and 73% among outpatients. There was no untoward effect of SVD in our study. The remission rate with combined infliximab and SVD for newly diagnosed CD was 100% (unpublished observation). Maintenance of remission on SVD was 92% at 2 years (Figure 2).^18,21 This was obtained without scheduled maintenance therapy with biologic drugs. Because these excellent short- and long-term results are not obtained by the current low-residue diet they can partly be explained by SVD.