Impact of Metabolic Health Patterns And Breast Cancer Over Time in Women

Background \& Rationale: Breast cancer (BC) is the most commonly diagnosed malignancy in women worldwide (2.1 million diagnoses in 2018, 25% of new cancer cases). In Canada, early stage BC mortality rates have decreased by 48% over the past 30 years as a result of advances in prevention, detection, and treatment. However, competing risks for mortality from non-cancer causes have emerged, where cardiovascular disease (CVD) is now a leading cause of death for BC survivors. The direct toxic effects of BC treatment on the heart (cardiotoxicity) are well characterized by the investigators and many others, as a contributor to elevated cardiovascular risk. However, BC treatment and the associated lifestyle changes (i.e. physical inactivity, poor diet quality, stress) are increasingly recognized to also strongly affect metabolism negatively manifesting as insulin resistance, dyslipidemia and adipose tissue (fat) accumulation. These adverse metabolic changes are strongly linked to CVD risk and represent a currently underappreciated contributor to the elevated CVD risk among BC survivors. Preliminary data and recent publications demonstrate that regional fat accumulation occurs during BC treatment and that the fat burden in key locations is associated with poor cardiorespiratory health. A trigger of these adverse metabolic and inflammatory effects is excess fat specifically within ectopic fat (viscera, intermuscular, or hepatic) regions. In 2019, a member of the study team found that the volume of visceral and intermuscular but not subcutaneous fat at BC diagnosis were linearly associated with CVD events within 6 years, even among those with normal BMI and after adjustment for pre-existing CVD risk factors and for BC treatment type. Using MRI, investigators found that \~1 year after chemotherapy, BC survivors had significantly larger depots of visceral fat (49% larger) and thigh intermuscular fat (41% larger) compared to age and sex-matched controls, despite similar BMI and subcutaneous fat volumes in the two groups. Investigators also showed that the fat fraction within the thigh muscle and visceral fat volumes independently explained \~50% of the variation in cardiorespiratory fitness (measured by peak VO2). In particular, peak VO2 is one of the most powerful predictors of all-cause and CVD mortality and health care costs, and is the most consistently reported negative sequelae after treatment for BC. Unfortunately, there are no known therapies to recover long-term myocardial damage (i.e. cell death, fibrosis) from cancer therapies. There are several reasons to target fat as a therapeutic target in BC patients: 1) The study team have compelling preliminary data showing accelerated formation of ectopic fat during BC treatment. 2) Investigator's recent data showed that high fat content in key fat pools was associated with reduced peak VO2. 3) The burden of fat and the associated metabolic abnormalities are dynamic and malleable, and thus highly treatable. Research Question \& Objectives: The primary purpose of this study is to evaluate the effect of a behavioural intervention involving supported time-restricted eating (TRE), diet quality improvements, and reduced sedentary time versus usual cancer and nutrition care in BC patients receiving chemotherapy treatment on ectopic fat, cardiometabolic profile, and chemotherapy outcomes. The investigators hypothesize that the intervention will attenuate the growth of ectopic fat during chemotherapy and reduce chemotherapy symptoms.