What are the investigators trying to do? By most measures, humans consume more food than needed. Over several decades, overconsumption has led to an increase in a number of diseases, including cancer. What if this could be reversed, or slowed down, by fasting? Would that improve how cancer patients respond to chemotherapy? Could simply changing eating patterns to reduce overall intake be a way to prevent and/or manage cancer? All of these are important questions and the investigators are undertaking a new initiative to study how nutrition and dietary behaviours affect cancer patients.

Fasting: A way to improve overall health and increase our defenses to cancer Fasting in various forms has been shown to have a number of health benefits. Intermittent fasting, or time restricted feeding, has been shown to reverse or improve various diseases such as diabetes, heart disease and metabolic syndrome, decrease the risk of cancer, and significantly extend the life of an individual. In previous studies, fasting was well-tolerated with notable improvements in energy levels, sense of well-being, and sleep quality. In cancer patients, clinical trials have demonstrated intermittent fasting to lessen some of the short-term side effects of chemotherapy such as nausea, fatigue, and sleep quality. How fasting alters the course of cancer or improve immune defenses is not yet known but may be an alternative way to treat or manage cancer.

The study plan The investigators plan to examine the effects of intermittent fasting (time restricted feeding) in patients with chronic lymphocytic leukemia (CLL). CLL is the most common chronic leukemia and is presently incurable. The advantage of choosing this patient population is that the cancer is easily assessed with a blood test measuring the amount of cancerous white cells (lymphocytes). Patients who consent to participate in this study will, through the support of an oncology dietitian and after a period of transition, split their daily feeding into a fasting period and a non-fasting period. This regime is as simple as skipping or having a late breakfast. At this time, participants will not be required to limit their total caloric intake.

What is required from the participant? The investigators will assess whether intermittent fasting reduces the cancer by measuring the lymphocyte count in the blood over a period of 3 months. Study participants will complete questionnaires to help determine if fasting causes any change in their quality of life. The effects of intermittent fasting on a cancer control system called autophagy, as well as its effects on inflammation will be studied in the Deeley Research Centre laboratory at BC Cancer.

What is the short- and long-term impact? In the short-term, if intermittent fasting can have an effect cancer lymphocyte count or on autophagy, then investigators will proceed with further studies to try and optimize the effects of intermittent fasting. In the long-term, this study is expected to be the first-ever to shed light on how intermittent fasting may be linked to cancer survival and/or growth. If true, this will open up new avenues to re-evaluate the inclusion of diet into cancer treatment protocols.

Inclusion Criteria:

• Diagnosis of CLL or SLL
• Age </=85
• Lymphocytes >/=40 and <150
• Hemoglobin >/=100g/L
• Platelet >100 x 10*9/L
• BMI of >/= 20kg/m2
• Eastern Cooperative Oncology Group (ECOG) Performance Status \