Table 1.

Methodological recommendations.

Study type	Target population	Dietary intake or intervention	Endpoint
Risk of endometriosis
Observational; cross-sectional or cohort study	Girls and women before menopause	Habitual intake assessed by FFQ (nutrients, foods)	Presence (cross-sectional) or new cases (cohort) of endometriosis based on complaints (questionnaires: EHP-30) and clinical confirmation by ultrasound, MRI or surgery
Associations between severity of subjective and clinical endometriosis complaints and diet
Cross-sectional study, observational or longitudinal study	Women with clinically confirmed endometriosis	Habitual intake of foods or nutrients by FFQ	Subjective outcomes: pelvic pain, mood and quality of life
			Clinical outcomes: subfertility; presence of endometriosis lesions on ultrasound, MRI or surgery and cyst size
Effect of diet on endometriosis-related complaints
Intervention, one group design with measurements before and after start of diet	Women with clinically confirmed endometriosis; subgroups based on type of endometriosis; use of oral contraceptives; past surgical treatment for endometriosis	Whole diet: (e.g. Mediterranean, healthy eating); Elimination diet: (e.g. low FODMAP); specific foods: (e.g. fruits and vegetables)	Subjective outcomes (e.g. pelvic pain, mood, quality of life) as assessed by questionnaires (EHP-30).
			Clinical outcomes (e.g. Inflammation markers, presence of endometriosis lesions on ultrasound, MRI or surgery; cyst size)
Intervention, parallel groups including placebo	Women with clinically confirmed endometriosis; subgroups based on type of endometriosis; use of oral contraceptives; past surgical treatment for endometriosis	Specific nutrients: (e.g. vitamin D or omega-6 fatty acids)	Subjective outcomes (e.g. pelvic pain, mood, quality of life) as assessed by questionnaires (EHP-30).
			Clinical outcomes (e.g. Inflammation markers, presence of endometriosis lesions on ultrasound, MRI or surgery, cyst size)
Mechanistic studies
Observational or intervention study	Women with clinically confirmed endometriosis	Any dietary intervention	Immune cells in peripheral blood and/or menstrual effluent: cytokines, neutrophils, granulocytes (including mast cells and macrophages), chemokines and different subsets of T-cells