Eat More Fiber, Not Less, During Pelvic Radiotherapy?

Megan Brooks

October 23, 2017

Results of a randomized controlled trial challenge long-standing advice to restrict dietary fiber during pelvic radiotherapy (RT). On the contrary, the study showed a "clear benefit" of increased fiber intake during pelvic RT.

Patients following a high-fiber diet during pelvic RT had less gastrointestinal (GI) toxicity both acutely and at 1 year compared with those who kept to their normal fiber intake, leading the researchers to conclude that restrictive, non–evidence-based advice to reduce fiber intake during pelvic RT should be abandoned.

The study was published in the September issue of the American Journal of Clinical Nutrition.

H. Jervoise Andreyev, PhD, FRCP, from the Royal Marsden NHS Foundation Trust in London, United Kingdom, and colleagues compared low-, high-, and habitual-fiber diets for prevention of GI toxicity in 166 patients undergoing radical (curative) pelvic RT with or without concomitant chemotherapy for gynecologic or lower GI cancer.

Fifty-five patients were randomly allocated to a low-fiber diet (≤10 g nonstarch polysaccharide [NSP]/d), 56 to a high-fiber diet (≥18 g NSP/d), and 55 to a control group maintaining usual fiber intake (habitual-fiber diet).  Patients in the low- and high-fiber diet groups received individualized counseling at the start of RT to achieve their fiber-intake targets.

GI toxicity was assessed as the severity of bowel symptoms experienced during the acute (baseline to 5 - 7 weeks) and chronic (1 year after completion of RT) period. Symptoms were assessed by using the Inflammatory Bowel Disease Questionnaire–Bowel Subset (IBDQ-B), which has been validated in the RT setting.

Patients in the three groups had similar IBDQ-B scores at baseline. Overall, IBDQ-B scores decreased in all groups during treatment, indicating worsening bowel symptoms, the researchers report.

Change in the IBDQ-B score, the primary endpoint, did not significantly differ between the baseline and nadir among the groups (P = .093).

However, the change in IBDQ-B score between the start and end of RT was smaller (better) in the high-fiber group than in the habitual-fiber group (mean, –3.7 vs –10.8). This is a clinically significant difference of 7.1 points (P = .011) and shows a "clear benefit" of increased fiber intake in this patient population, the researchers note.

Patients eating a high-fiber diet also had improved GI symptoms 1 year after RT compared with those eating a normal diet (IBDQ-B score, 0.1 vs –8.4). 

The observation that at 1 year after RT, the difference in score between these groups was 8.5 points (P = .004), "indicating a longer-term effect, fits with the current concepts of radiotherapy toxicity that encompass the consequential effect…namely that severe acute toxicity predisposes to longer-term severe toxicity," the researchers write. These differences between groups in the change in IBDQ-B score are equal to a 10% or greater change, which has previously been defined as "meaningful clinical improvement," they point out. 

A low-fiber diet did not show any improved GI toxicity compared to normal diet.

The dietary interventions had no adverse effect on body weight or total energy intake, and there were no significant between-group differences in stool frequency or form or number of days on which loose or watery stools were experienced. "Thus, the premise that increased fiber exacerbates a tendency toward treatment-induced diarrhea appears to lack physiologic foundation," Dr Andreyev and colleagues write.

The investigators were not able to determine whether any specific component or type of fiber confers most benefit (readily vs poorly fermentable) because all foods contain a diverse range of fiber substrates.

Summing up, they note that therapeutic RT is "an important treatment of pelvic cancers. Historically, low-fiber diets have been recommended despite a lack of evidence and potentially beneficial mechanisms of fiber." But on the basis of their findings, they recommend that advice to reduce fiber intake during pelvic RT be "discarded."

"This is a well-conducted study [and] there are few randomized studies on this topic so this is fairly unique," Vishal Gupta, MD, associate professor of radiation oncology at the Icahn School of Medicine at Mount Sinai in New York City, who wasn't involved in the study, told Medscape Medical News.

"Although this is a very interesting study, it is relatively small (116 patients) with various malignancies (rectal, anal, endometrial, cervical) that are treated with different radiation doses and chemotherapy agents (specific agents not reported)," Dr Gupta noted. "All of these factors would influence GI toxicity. Although this may not be practice changing, it does suggest that a low-fiber diet is not beneficial in patients undergoing pelvic RT and that a high-fiber diet may actually be preferable in terms of GI toxicity."

The study was supported by the Royal Marsden Cancer Charity and the National Institute for Health Research for the Royal Marsden/Institute of Cancer Research, Biomedical Research Centre.  The authors and Dr Gupta have disclosed no relevant financial relationships.

Am J Clin Nutr. 2017;106:849-857. Abstract

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