Time Restricted Eating in Haematological Malignancies

The goal of this clinical trial is to learn if time restricted eating (TRE), a form of intermittent fasting, can impact health outcomes in patients with chronic lymphocytic leukemia (CLL). The main questions it aims to answer are:

* In patients with CLL, is there a decrease or stabilization in cancer cell counts associated with TRE compared to baseline? * Is there a decrease in immune cell autophagy (a cellular recycling process) activity associated with TRE compared to baseline? * Does adherence to a TRE regimen improve patient experience and quality of life?

Immune cell autophagy activity in cancer patients will be compared to a subset of control participants without cancer.

Participants will:

* Adhere to a 16/8 fasting regimen, which involves eating as normal for 8 hours per day and fasting (only consuming water, black coffee or black tea) for the remaining 16 hours. They will follow this intervention for their choice of either 3 or 6 months. * Complete monthly blood collections * Complete weekly journal entries to record weekly weight and timing of first and last daily meals * Complete weekly safety check-ins with a study team member for the first 4 weeks of the study and then bi-weekly thereafter * Complete 3 quality of life questionnaires * Provide 3 stool samples (optional component of study) * Complete an end of study interview (optional component of study)