Inclusion Criteria:  Women with a surgical, imaging, or clinical diagnosis of endometriosis Age 18-45 years Stable health condition and medications for past 3 months Modified Biberoglu and Behrman (B&B) pelvic pain score of at least 5/9 Able to follow a plant-based diet for 12 weeks Willing to be randomly assigned to either a plant-based group or a control group that will not make any dietary changes for 12 weeks  Exclusion Criteria:  Body mass index ≥ 40 kg/m2 Smoking or drug abuse during the past six months Alcohol consumption of more than 2 drinks per day or the equivalent, episodic increased drinking (e.g., more than 2 drinks per day on weekends), or a history of alcohol abuse or dependency followed by any current use Unstable medical or psychiatric illness Already following a plant-based diet Pregnant or breastfeeding, or plans of pregnancy within the study period Hysterectomy or ovariectomy Fibroids, ovarian cysts, pelvic inflammatory disease Endocrine inflammatory conditions, such as Cushing's syndrome, Hashimoto's thyroiditis, Graves' disease, type 1 diabetes mellitus, and Addison's disease Lack of English fluency Unable or unwilling to participate in all components of the study Evidence of an eating disorder