Purpose Radiotherapy to the prostate gland and pelvic lymph nodes may cause acute and late bowel symptoms and diminish quality of life. The aim was to study the effects of a nutrition intervention on bowel symptoms and health-related quality of life, compared with standard care. Methods Patients were randomised to a nutrition intervention (n = 92) aiming to replace insoluble fibres with soluble and reduce intake of lactose, or a standard care group (n = 88) who were recommended to maintain their habitual diet. Bowel symptoms, health-related quality of life and intake of fibre and lactose-containing foods were assessed up to 24 months after radiotherapy completion. Multiple linear regression was used to analyse the effects of the nutrition intervention on bowel symptoms during the acute (up to 2 months post radiotherapy) and the late (7 to 24 months post radiotherapy) phase. Results Most symptoms and functioning worsened during the acute phase, and improved during the late phase in both the intervention and standard care groups. The nutrition intervention was associated with less blood in stools (p = 0.047), flatulence (p = 0.014) and increased loss of appetite (p = 0.018) during the acute phase, and more bloated abdomen in the late phase (p = 0.029). However, these associations were clinically trivial or small. Conclusions The effect of the nutrition intervention related to dietary fibre and lactose on bowel symptoms from pelvic RT was small and inconclusive, although some minor and transient improvements were observed. The results do not support routine nutrition intervention of this type to reduce adverse effects from pelvic radiotherapy.

Aim Men with prostate cancer undergoing radiotherapy may experience acute and late bowel symptoms. Nutrition interventions have shown some benefits, however, adherence tends to decline over time. Qualitative studies, carried out after an intervention, are important to help explain trial results. The aim of the present study was to explore patient experience of participating in a nutrition intervention in a randomised controlled trial, with a focus on facilitators and barriers to adherence. Methods Semistructured interviews were conducted with 15 men with prostate cancer recruited from a randomised controlled trial on a nutrition intervention during radiotherapy. Interviews were analysed with content analysis with an inductive approach. Results The informants were motivated to make dietary changes to avoid bowel symptoms. Social support, a feeling of contributing to the greater good, prior knowledge, dietary information and a small need for behaviour change facilitated adherence. Feeling limited, wanting to decide for themselves, the timing of the intervention, unmet expectations of dietary advice and loss of motivation, were described as barriers for adherence. Conclusions Future nutrition intervention trials may benefit from involving significant others to a greater degree, as well as offering pre‐set recipes and strategies to manage social events, and more sessions with the dietitian for patients in need of more support. Tailored interventions based on the individual's preferences, context and prior knowledge about food may further facilitate adherence.

Objectives: A variety of non-evidence-based dietary advice on modified fibre and lactose intakes are provided to patients undergoing pelvic radiotherapy to counteract treatment-related bowel symptoms. More knowledge on the nutritional consequences of such advice is needed. This study aimed to explore how advice on modified fibre and lactose intakes during pelvic radiotherapy was associated with nutrient intakes amongst patients with prostate cancer. Methods: A total of 77 Swedish men who underwent radiotherapy (50/2 Gy + boost 20–30 Gy) in 2009–2014 due to prostate cancer were given dietary advice at radiotherapy onset (baseline) and at 4 and 8 weeks after radiotherapy onset, to modify their fibre and lactose intakes. At baseline, the participants completed a food frequency questionnaire (FFQ) and a 24-h dietary recall. At 4 and 8 weeks, the participants completed the FFQ and a 4-day estimated food record. Fibre and lactose intakes were measured by intake scores calculated from the FFQs. Multiple linear regression models were used to analyse associations between intake scores and fibre- and lactose-related nutrients. Results: In adjusted analyses, there were few significant associations between dietary advice on modified fibre and lactose intakes and observed intakes of fibre- and lactose-related nutrients. A more modified lactose intake was thus associated with a lower intake of calcium (P = 0.041), whilst a more modified fibre intake was associated with a higher value for the change in intake of vitamin C (P = 0.016). Conclusions: Dietary advice on modified fibre and lactose intake was in most cases not significantly associated with altered nutrient intakes, rather the energy and nutrient intakes were mostly stable during the pelvic radiotherapy. More research is needed on the nutritional consequences of dietary advice on modified fibre and lactose intakes to reach consensus on if they should continue to be provided in the clinic.