Pettersson, A., Johansson, B., Persson, C., Berglund, A., & Turesson, I. (2012). Effects of a dietary intervention on acute gastrointestinal side effects and other aspects of health-related quality of life: A randomized controlled trial in prostate cancer patients undergoing radiotherapy. Radiotherapy and Oncology, 103(3), 333–340.

To examine the effect of decreased intake of insoluble dietary fiber and lactose on acute gastrointestinal (GI) side effects and other aspects of health-related quality of life (QOL) in patients with localized prostate cancer receiving radiotherapy (either brachytherapy or proton therapy)

Patients in the intervention group were instructed to avoid foods high in insoluble dietary fiber and lactose and to consume foods higher in soluble fibers and low in lactose beginning at baseline and continuing for 24 months past the completion of radiotherapy. Patients in the standard care group were instructed to continue their normal diet during this time period. Data was collected at four time points: prior to randomization and initiation of radiotherapy, after four weeks of treatment, one week after radiotherapy completion, and two months after completion of radiotherapy.

• The study consisted of 113 patients, with 55 in the intervention group and 58 in the standard care group.
• Median age was 66 years with a range of 50–77 years.
• The sample was 100% male.
• All patients had localized prostate cancer.
• Patients were excluded from the study if they had received prior radiation therapy to the pelvic/bowel area, had been diagnosed with inflammatory bowel disease, had cognitive dysfunction, had long-term hospitalization, or were unable to speak or understand Swedish.

This was a single-site, outpatient study conducted in Uppsala, Sweden.

Patients were undergoing multiple phases of care.

This was a randomized controlled trial.

• The European Organization for Research and Treatment of Cancer (EORTC) Core Questionnaire (EORTC QLQ-C30) and Prostate Module (EORTC QLQ-PR25) were used to assess factors such as constipation, diarrhea, limitations on activities of daily living, and unintentional leaking of stools.
• The Gastrointestinal Side Effects Questionnaire (GISEQ), a study-specific questionnaire, was used to assess how bothered patients are by GI side effects.
• A scale indicating adherence to dietary instruction (lower score = better compliance) was developed from a Food Frequency Questionnaire (FFQ).

Both the intervention group and the standard care groups followed dietary instructions as indicated by an interaction effect between randomization and time in the FFQ scores (p ˂ 0.001).  The dietary intervention had no statistically significant effect on GI side effects or other aspects of QOL, although bowel symptoms were lower in the intervention group.

The dietary intervention of decreased intake of insoluble dietary fibers and lactose did not have an effect on acute GI side effects in patients with localized prostate cancer undergoing radiotherapy (either brachytherapy or proton therapy).

• Key sample group differences could have influenced results.
• Comorbidities of pulmonary disease, cardiovascular disease, rheumatic disease, obesity, older age, and a history of smoking were more common among the patients in the intervention group. The authors sited references indicating that patients with comorbidities and older patients are more likely to develop GI toxicity. These group differences could have impeded the effect of the intervention.

Although this study did not show that a diet with reduced intake of insoluble dietary fiber and lactose had a significant effect on GI side effects, it did show a tendency toward lower prevalence of bowel symptoms in the intervention group during radiotherapy, which suggests the intervention may have had a positive effect. Controlling for health status in future studies might lead to a different outcome. Also, patients in this study had localized prostate cancer where a small part of the rectum was in the field of irradiation. Future research should evaluate the effect of the diet intervention in patients with lymph node positive disease, which would involve a larger bowel volume in the radiation field and increase the possibility of GI toxicity.