Fasting

The goal of this randomized controlled parallel group trial is to examine if fasting before and after chemotherapy is safe, feasible and acceptable. The study population will include patients with either Hodgkin lymphoma or Diffuse Large B Cell Lymphoma. The main questions aimed to answer are: Whether fasting during chemotherapy is safe for patients, whether it is feasible to implement in a clinical setting, and whether patients find it acceptable. We also want to examine a number of patient-reported outcome measures regarding health status and quality of life, such as dietary intake and adverse events from chemotherapy. Researchers will compare fasting to standard treatment. Participants will: * Fast 24 hours before and 24 hours after chemotherapy in addition to standard treatment or receive only standard treatment * Keep a diary of their dietary intake 24 hours before and 24 hours after chemotherapy * Keep a diary of their dietary intake for three consecutive days between chemotherapy cycles * Answer questionnaires/questions in relation to side effects from fasting, side effects/adverse events of chemotherapy, quality of life * Take bioimpedance analysis (including body mass index and body composition) * Take blood- and feces samples

Activating the immune system to kill cancer cells is a promising therapeutic strategy for some patients with cancer. Unfortunately, current immune-targeting treatments do not work for patients with prostate cancer. In animal models of cancer, fasting can reprogram the body's metabolism and immune cell function to help immune cells kill cancer cells likely by increasing ketosis. The purpose of this study is to determine whether 7 days of water-only fasting or a ketogenic very low-calorie diet or ketone supplementation is safe and feasible for patients with prostate cancer. This will help the investigators develop future studies to test whether incorporating periods of fasting or very low calorie diets or a ketone supplement into treatment plans for prostate cancer can improve outcomes from this disease.