Table 1.

Eligibility criteria for participants and donors

Participants	Donors
Inclusion
Biological female at birth	Biological female at birth
16–32 years of age	18–32 years of age
BMI 13–19 kg/m2	BMI 18.5–25 kg/m2
Formal diagnosis of AN by an eating disorder specialist*	Total body fat ≤33% (as assessed by whole-body DXA)
Medically stable†	Healthy diet (≥4 portions of fruit and/or vegetables/day)
Able and willing to swallow the treatment capsules	Regular exercise (moderate-to-vigorous physical activity for ≥3.5 hours/week)
Able and willing to comply with the clinical assessments	Regular bowel habit (passing stools at least once every 2 days)
Exclusion
Known allergies to any foods or medications	Positive screening test for any transmissible pathogen or multidrug resistant organism listed in table 2
Use of antibiotics or probiotics in the month prior to treatment	Gastrointestinal disease (eg, inflammatory bowel disease, irritable bowel syndrome, coeliac disease or eosinophilic oesophagitis)
Regular oral steroid treatment or daily application of potent topical steroids extensively to the body	Metabolic disorder (eg, diabetes, metabolic syndrome, hypertension, dyslipidaemia or dysglycaemia)
Compromised immune system	Impaired fasting glucose (>5.9 mmol/L) or elevated HbA1c (>41 mmol/mol)
Any other chronic illness affecting gut or metabolic health	Asthma or eczema requiring regular prophylaxis or treatment
Thoughts of self-harm and/or suicidal ideation‡	Autism spectrum disorder
Current or planned pregnancy during the course of the study	Previous diagnosis of mental health issues including eating disorders
Regular laxative use	Current or history of malignancy
	Use of oral antibiotics or probiotic supplements in the past 3 months
	Regular binge drinking (>5 standard alcoholic units per session at least once a week)
	Past or present use of recreational drugs, tobacco or vaping
	Current or past pregnancy
	Overseas travel in the past 2 weeks§

*Meeting the DSM-5 criteria, 307.1.

†In accordance with Starship Children’s Hospital’s clinical guidelines⁷⁰ (ie, resting heart rate >50 bpm; no postural drop in blood pressure or rise in heart rate, no electrolyte abnormalities, and temperature >35°C and <37.8°C).

‡Based on response to question 9 of the Patient Health Questionnaire-9 (PHQ-9).⁶⁰

§Donors who have travelled overseas will need to wait a minimum period of 2 weeks from their arrival back in New Zealand before donating.

AN, anorexia nervosa; BMI, body mass index; DSM-5, Diagnostic and Statistical Manual of Mental Disorders, fifth edition; DXA, dual-energy X-ray absorptiometry.