The aim of this study is to investigate whether Lactobacillus reuteri could have a beneficial role in treatment of children and adolescents with Anorexia nervosa who develop motility disorder due to the malnutrition regarding the normalization of the motility, as well as the possible role of probiotics on nutritional recovery, especially on bone health.

Pediatric patients with AN and constipation referred to gastroenterologist for nutritional rehabilitation at the Department of Pediatric Gastroenterology, Hepatology and Nutrition, Clinical Hospital Center Sestre Milosrdnice, Zagreb, approximately 30 children, will be asked to participate.

The evaluation of patients will be conducted through APA DSM-V diagnostic criteria for anorexia nervosa and Rome III criteria for constipation.

During the hospitalization all of the patients will receive conventional nutritional rehabilitation that is composed of serving normal food under supervision of nurses that calculate daily caloric intake through 5-6 meals and according to that additional enteral nutrition that consist of polymeric enteral formula. Daily caloric intake is calculated as kcal/kg/day and is slowly rising through 2 weeks starting from 80% to the goal of 130% of daily energy requirements according to FAO 2004 recommendation.

Anthropometry measures will be taken at the time of hospitalization and at every visit.

Normalization of weight is when the Z-score for BMI is less than -1.5 according to CDC BMI-growth charts, or normalisation of menstrual cycle is achieved.

In order to achieve adherence to therapeutic protocol parents will be contacted by phone at least once in 7-10 days. Participants will be instructed to keep diary on a daily basis (adherence to therapy, stool diary). All patients will return packages with all used, and unused product.

BASELINE -VISIT 1 Randomization at first day of hospitalization. In all patients anthropometry will be performed at the time of hospitalization, as well as dual-energy X-ray absorptiometry (DEXA) and serum D3 levels at first 2 days of hospitalization as a part of routine diagnostic protocol in heavily underweight patients with AN.

VISIT 2 4 weeks after randomization, at discharge from hospital Anthropometry

VISIT 3 8 weeks after randomization, 4 weeks after discharge from hospital Anthropometry

END OF STUDY -VISIT 4 3 months after baseline Anthropometry

VISIT 5 3 months after the end of study (6 months after baseline) At this point control serum D3 levels and DEXA will be performed at all patients Anthropometry

All the symptoms and daily caloric intake will be monitored using diaries attached to protocol.

Inclusion Criteria:

• Pediatric patients with Anorexia nervosa and constipation, aged 8-18 years

Exclusion Criteria:

• AN and constipation present for less than 3 month prior to hospitalization
• any disease that affects GI or other systems other than AN or functional constipation
• chronic disorder other than AN
• receiving probiotic and/or prebiotic products 14 days prior to enrolment
• receiving antibiotics 14 days prior to enrolment
• constipation prior AN
• receiving laxative as a therapy for constipation or abuse of laxative to lose weight prior to enrolment
• extraintestinal symptoms: fever, rash
• abnormalities in laboratory findings
• abnormalities in clinical findings: organomegaly, perianal disease

During the study, 6 months / participant,

The limitation of this study is the small number of patients. This is due to strict inclusion and exclusion criteria, as well as the fact that some parents and patients refused to participate in the survey, which is not unusual given the negativism that characterizes this disease.