The role of plant-food components in pelvic-organ cancer survivors - From feasibility to effects in randomized controlled dietary interventions

Abstract

Background: The number of people who are surviving cancer is steadily growing. Dietary components have a potential role in preventing the side effects of treatment for pelvic-organ cancer, as well as tumor recurrence in survivors. However, the evidence for such specific dietary advice is currently lacking. Large-scale randomized controlled trials are needed to strengthen the evidence for the effects of dietary components in pelvic-organ cancer survivors. Since compliance is one of the challenges in dietary interventions, digital tools could provide an effective method of measuring compliance. However, new methods need to be validated against a more established method to assess their precision in correctly measuring dietary intake. Aim: The aim of this thesis was to test the feasibility of a dietary fiber intervention prior to conducting a large randomized controlled trial in patients with pelvic organ cancer. Secondly, to investigate the effect of a diet high in phytoestrogens on tumor proliferation and if the effect differs between men with different genotypes of estrogen receptor beta (ERβ) in a large randomized controlled trial in patients with prostate cancer. Lastly, to develop and evaluate a new digital dietary assessment method for measuring dietary fiber intake. Methods: A dietary fiber intervention, using a fiber supplement and a moderate fiber intake from the regular diet, was tested in a feasibility study in patients with gynecological cancer (n = 57, Paper I). A study-specific food frequency questionnaire and a digital application were used, and blood and fecal samples were collected. The effects of a phytoestrogen intervention, using soybeans and flaxseeds, were tested in a randomized trial with patients with prostate cancer (n = 140, Papers II–IV). Tumor proliferation was measured as a Ki-67 index in tumor specimens, and prostate-specific antigen (PSA) and hormone concentrations were measured in the blood. A randomized crossover trial was used to validate the digital application against a 3-day dietary record to measure dietary fiber intake in a randomly selected female population (n = 26, Paper V). Results: In the Feasibility study, expected burden of the study or acute side effects of radiotherapy were the most common reasons for declining participation or dropping out (Paper I). The participation rate was highest for blood sampling and lowest for fecal sampling. The phytoestrogen intervention decreased the risk of a higher Ki-67 index, and the effect was most pronounced among men with a specific genotype of ERβ (Paper III). An opposite effect was seen on comparing the groups of ERβ genotypes where the phytoestrogen diet increased or decreased the risk of increased total PSA concentration. The phytoestrogen intervention did not affect blood concentrations of hormones except for decreased risk of increased estradiol concentration in one of the ERβ genotype groups (Paper IV). In the Dietary validation study, a ~2 g difference in measured fiber intake was found between the dietary record and the digital application (Paper V). Conclusions: Dietary interventions with dietary fiber supplements and phytoestrogen-rich foods are feasible in patients with pelvic-organ cancer and digital tools can be used for the assessment of dietary fiber intake. The design of interventions needs to be carefully adapted to the targeted group to be feasible. The effects of the plant-food components need further investigation. The results of this thesis can be useful for both clinicians and researchers.