BACKGROUND: Longitudinal studies suggest that diets encouraging higher intake of fruits and vegetables and lower intake of red meat are associated with a lower risk of laparoscopically-confirmed endometriosis. However, no studies have examined whether plant-focused dietary patterns are associated with endometriosis risk. OBJECTIVE: To investigate the association between three plant-based diet indices and the risk of laparoscopically-confirmed endometriosis in a predominantly omnivorous population. METHODS: We followed 82,084 premenopausal women participating in Nurses' Health Study II for 30 years. Diet was assessed using a validated food frequency questionnaire every 4 years. We calculated an overall plant-based diet (PDI), a healthful plant-based diet (hPDI), and an unhealthful plant-based diet (uPDI); higher scores indicated greater intake of plant foods and lower intake of animal foods. Laparoscopically confirmed endometriosis was ascertained from 1993. We used Cox proportional hazards models with age in months to calculate hazard ratios (HRs) and 95% confidence intervals (CIs). RESULTS: During 1,038,888 person-years of follow-up, 3,829 cases of laparoscopically-confirmed endometriosis were reported. We observed no association between PDIs and endometriosis risk. The HR of each plant-based diet index with multivariable-adjusted models comparing participants in the highest quintile of adherence to those in the lowest quintile were 1.01 (CI=0.91, 1.13) for PDI, 1.07 (CI=0.96, 1.20) for hPDI, and 1.05 (CI=0.94, 1.16) for uPDI. Estimates were consistent regardless of infertility status. CONCLUSIONS: This study suggests that variation in the proportion of plant to animal foods, as captured by plant-based diet indices within predominantly omnivorous population is unrelated to risk of laparoscopically-confirmed endometriosis.
Mitsunami et al. (Sat,) studied this question.