Dietary Intake During Chemotherapy and Its Association with Changes in Cardiometabolic, Biochemical, and Psychological Outcomes in Women with Breast Cancer: A Prospective Cohort Study Protocol

Background: Chemotherapy is a cornerstone of breast cancer treatment but is often accompanied by metabolic, hematological, and psychological changes that may negatively affect patients' health and quality of life. Dietary intake during chemotherapy may influence these treatment-related outcomes; however, prospective evidence based on repeated dietary assessments and comprehensive clinical outcomes remains limited. Objective: The primary objective of this study is to investigate the association between dietary intake during chemotherapy and changes in a predefined composite cardiometabolic risk profile in women with breast cancer. Secondary objectives are to evaluate associations of dietary intake with selected biochemical and psychological outcomes. Methods: In this prospective cohort study, 100 women with histologically confirmed breast cancer undergoing chemotherapy in Tehran, Iran, will be followed from the initiation of chemotherapy until completion of the planned chemotherapy course. Dietary intake will be assessed using nine repeated dietary records collected during the early, mid, and late phases of chemotherapy, and mean intake will represent overall dietary exposure during treatment. Cardiometabolic, biochemical, and psychological outcomes will be assessed at baseline and post-chemotherapy using clinical measurements, laboratory data, and validated questionnaires. Descriptive within-participant changes will be defined as post-chemotherapy minus baseline values and evaluated using paired tests. The primary analysis will examine the association between dietary intake during chemotherapy and the post-chemotherapy composite cardiometabolic risk score using multivariable linear regression adjusted for age, baseline BMI, mean energy intake during chemotherapy, physical activity level at the end of chemotherapy, tumor stage, treatment type, and the baseline composite score. Secondary analyses will use the same baseline-adjusted framework for selected biochemical and psychological outcomes. Exploratory analyses will also examine end-of-chemotherapy serum vitamin D concentration as a concurrent biomarker associated with end-of-treatment outcomes. Results will be reported as beta coefficients with 95% confidence intervals. Conclusion: This study will provide prospective evidence on the relationship of dietary intake and end-of-chemotherapy serum vitamin D status with treatment-related cardiometabolic, biochemical, and psychological changes in women with breast cancer. Keywords: Breast cancer; Chemotherapy; Dietary intake; Cardiometabolic risk factors; Quality of life; Prospective cohort study.