Dietary Intake During Breast Cancer Treatment and Its Association with Changes in Cardiometabolic Risk Markers and Psychological Outcomes in Women with Breast Cancer: A Prospective Cohort Study Protocol

Background: Active systemic therapy, including chemotherapy alone or combined with HER2-directed targeted therapy, is a cornerstone of breast cancer management, yet it frequently precipitates adverse cardiometabolic, anthropometric, and psychological disturbances. Although dietary intake during active treatment may modulate these complications, rigorous prospective cohort evidence utilizing repeated dietary assessments and standardized clinical endpoints remains limited. Objective: The primary objective of this prospective cohort study is to investigate the longitudinal association between dietary intake during active cancer treatment and changes in the visceral adiposity index (VAI), serving as the primary cardiometabolic endpoint, among women with breast cancer. Secondary objectives are to examine associations between dietary exposures and individual cardiometabolic markers, body composition, psychological distress, and health-related quality of life. Methods: A prospective cohort of 100 women with histologically confirmed primary breast cancer is recruited at the initiation of systemic therapy and followed prospectively for six months in Tehran, Iran. The cohort encompasses patients undergoing standard chemotherapy regimens (spanning 4.5 to 6 months), including those receiving sequential HER2-directed targeted therapy. Habitual dietary intake during active treatment is assessed using nine 24-hour dietary records systematically distributed across the early, middle, and late treatment phases (incorporating weekdays and weekend days). Clinical, anthropometric, biochemical, and psychological outcomes are evaluated at baseline (pre-treatment) and at the 6-month follow-up. Primary multivariable linear regression models will specify the 6-month VAI as the dependent variable, adjusting for its baseline level, age, baseline body mass index, tumor stage, active treatment regimen, follow-up physical activity, and total energy intake. Secondary analyses will evaluate key secondary cardiometabolic parameters, psychological outcomes, and exploratory end-of-study serum 25-hydroxyvitamin D concentrations. Regression results will be reported as unstandardized coefficients (B) with 95% confidence intervals and standardized coefficients ({beta}). Conclusion: This prospective protocol outlines a standardized methodology to determine whether dietary intake during active systemic therapy tracks with adverse cardiometabolic trajectories and psychological burden, generating crucial evidence to inform tailored nutritional interventions during active breast cancer treatment.