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)

Inclusion Criteria:

Experimental Participants:

• Diagnosis of CLL or SLL, Age 18-85
• Peripheral blood lymphocytes >20 x 10^9/L
• Hemoglobin >90g/L
• Platelets ˃90 x 10^9/L
• BMI of >=20kg/m2
• ECOG Performance Status >=2
• Not following any form of IF for 4 months prior to study

Control Participants:

• Absence of cancer diagnosis (active or historical)
• Age 18-85, Peripheral blood lymphocytes <5 x10^9/L
• BMI of >=20kg/m2
• ECOG Performance Status >=2
• Not following any form of IF for 4 months prior to study

Exclusion Criteria:

Experimental and Control Participants:

• Unable to give consent
• On medications required to be taken with food during the fasting window
• Pregnant or breastfeeding
• Diabetes mellitus
• BMI drop to < 18.5kg/m2 at any time during study
• Anti-lymphoma therapy within the past 3 months
• Expected to initiate anti-lymphoma therapy within the next 3 months
• Unable to fast due to a digestive system disorder
• > 85 years of age (due to frailty, increased risk of infection, and burden of additional blood collections)

IPD will be available through OSF upon study completion. The protocol will be published.

Will be available upon study completion (estimated date of September 2027) and will remained available for 10 years.

The aforementioned data will be made publicly available following study completion via OpenScienceFramework webpage. Additional data may be shared upon requested to study Principal Investigator.