Dietary Fibre Supplementation to Delay Disease Progression in Early Prostate Cancer

Active surveillance (AS) is commonly recommended for men diagnosed with localised prostate cancer who have a low risk of tumour spread. If the prostate cancer progresses to a more aggressive form, this will require active treatment - typically surgical removal of the prostate (radical prostatectomy) or radical radiotherapy to the prostate.

At Aberdeen Royal Infirmary (ARI) Urological unit, the AS protocol involves repeat MRI scans and biopsies being performed at the end of year 1, followed by subsequent radiological and histological investigations every two years, accompanied by either 3- or 6-monthly routine monitoring of specific biochemical (i.e. prostate-specific antigen) levels. In other words, AS is a clinical pathway that aims to monitor early prostate cancer, rather than treating it straight away.

Men undergoing AS, an often-overlooked group in the literature, experience certain levels of cyclical anxiety. This cohort may experience persistent apprehension regarding disease progression, with the fear lingering in the background of their thoughts. Anxiety intensifies around routine appointments with the AS protocol, and new concerns may emerge, particularly relating to fluctuations in their PSA levels. In a recent descriptive analysis, it was found that out of the 43.6% of men who discontinued AS after five years, roughly 12.8% of dropouts occurred because they converted to active treatment without any evidence of disease progression. Therefore, a considerable number of patients exhibit a strong inclination to actively engage in lifestyle modifications in an effort to attempt the prevention of disease progression. This approach includes an interest in modifying their dietary habits.

Dietary fibre, such as psyllium and inulin, are non-digestible carbohydrates that are found in fruits, vegetables, whole grains and legumes. The gut microbiota anaerobically ferments dietary fibre, producing short-chain fatty acids (SCFAs), including acetate, propionate and butyrate. SCFAs play a pivotal role in the intricate relationship between food, gut microbiota and health, exhibiting notable anti-inflammatory and anti-tumorigenic properties.

In a population-based case-only study conducted in the USA, higher fibre intake was inversely associated with prostate cancer aggressiveness (odds ratios 0.70, 95% confidence interval 0.50-0.97 and 0.61 95% CI 0.40-0.93, for 2nd and 3rd tertiles of total fibre intake, respectively). Additionally, a prospective phase II dietary intervention study, using the fibre supplement modified citrus pectin in men with non-metastatic prostate cancer who had biochemically relapsed, showed promising results. 78% of men responded to the therapy, with 58% having a decreased or stable PSA and 75% an improvement in PSA doubling time (PSADT), and median PSADT was significantly improved (p=0.003).

The Kiltie Lab and others have demonstrated the benefit of the rapidly fermented, soluble dietary fibre inulin in controlling tumour growth in mice compared to low dietary fibre intake, in a range of tumour types (including prostate, colorectal cancer and bladder cancer). However, this can come at the expense of side effects in humans including flatulence and bloatedness. Psyllium is another fibre which is commonly used to treat constipation but it is also widely used to treat the diarrhoea caused by radiotherapy to the prostate region. Recently, the addition of psyllium was found to significantly reduce gas production in the colon from the fermentation of inulin, in human subjects with irritable bowel syndrome.

Given this body of evidence, the investigators would like to explore and evaluate the attitudes of patients regarding the potential of dietary fibre supplementation during AS. It is hoped that this qualitative research will provide valuable insights that will support and inform the development of a pilot and feasibility studies on dietary fibre supplementation for prostate cancer patients on AS, delaying the time to active treatment or obviating its use. Subsequently, the intention is to establish a UK multicentre, randomised controlled trial. This may subsequently change clinical practice for patients with prostate cancer on AS.

Inclusion criteria

• Participants over 18 years of age.
• Participants with residence in North-East Scotland.
• Participants must be fluent in the English language.
• Participants on active surveillance.

Exclusion criteria

• Participants who do not speak fluent English will be excluded from this study.
• Participants who were treated with surgery, radiotherapy, chemotherapy or anti-androgen therapy for their prostate cancer.
• Vulnerable participants, classified as adults who do not have the capacity to consent for themselves, will not be included in the study. If the research team are made aware that someone has lost capacity then they will be withdrawn from the study.