In recent years, many studies have shown the positive effect of certain types of fasting on human health, particularly on obesity, diabetes, and aging. In particular, the beneficial effects of intermittent fasting are gaining more attention among clinical researchers. Intermittent fasting is the voluntary abstinence of individuals, from food (some or all food, drinks, or both) for a period longer than a typical overnight 12 h fast. The digestibility of food is an important characteristic, associated with the concepts of health and well-being. Digestive motility disorder leads to various digestive problems like difficulty in swallowing, acid reflux disease, severe constipation, diarrhea, abdominal pain, vomiting, and bloating. Hence the investigators aimed to assess the impact of intermittent fasting (religious fasting "Ramadan") on digestibility (gastrointestinal motility), weight, blood glucose level, gut microbiota, and gut permeability of the subjects. A cohort of 21 subjects homogeneously distributed by sex, age, and BMI will be prospectively enrolled and involved in the study. By comparing the analytical data before and after Ramadan the effect of intermittent fasting on digestibility, blood glucose and microbiota will be characterized by the investigators.

The study has been developed as a clinical trial. It is expected the signing of the informed consent and authorization to the personal data (attached information form - Consent and information GDRP). A total of 21 subjects aged between 20 and 60 years homogeneous for sex (10M:11F) and body mass index (BMI = kg/m2) will be enrolled for the study. Subjects will be required to practice a 29/30 day religious fast.

All subjects will provide two stool samples for 16S rRNA sequencing, first at baseline and the second after 30 days of Ramadan for gut microbiota assessment. In addition, at the beginning of the study, subjects will be submitted to complementary and validated semi-quantitative questionnaires to assess the severity, frequency, and duration of the gastrointestinal symptoms in the month prior to the start of the study, the study of gastric and cholecystic motility, the assessment of the oro-cecal transit time. In addition, at the beginning of the study, during and after fasting, subjects will be complementary and validated semi-quantitative food questionnaires to evaluate the diet.

Gastric and cholecystic motility will be assessed using a portable ultrasound scanner (Esaote AU450 and Noblus, Hitachi Medical, Tokyo, Japan) equipped with a 3.5 MHz convex probe in order to measure time-dependent changes in fasting and post-meal cholecyst volumes and gastric antral areas. All experiments will begin at 08:00 after an overnight fast of 12 hours. Gastric and cholecyst motility will be compared after the standard meal (Nturi ENSUR) ingested along with a 120 ml glass of water in which 15 ml of lactulose will be dissolved. Lactulose provides a non-absorbable but fermentable substrate useful for measuring the oro-cecal transit time (OCTT). The solution will be drunk at room temperature for one minute in the presence of the examiner.

Transit times will be measured using breath testing, following standard guidelines. During the 30 days prior to the test, subjects should not take antibiotics, probiotics, prokinetics, or other medications that affect gastrointestinal motility and gut microbiota. To avoid prolonged intestinal production of H2 due to the presence of non-absorbable or slowly fermentable foods, each subject should follow a special diet the day before the test consisting of meat, fish, and olive oil. No other fermentable foods or sugary drinks will be allowed. Breath samples will be taken before ingestion of the test meal and then every 15 minutes for 120 minutes after ingestion of the meal using a pre-calibrated portable hydrogen-sensitive electrochemical device (EC60-Gastrolyzer, Bedfont, USA). Results will be expressed as excretion of H2 in parts per million (p.p.m). The 10 p.p.m increase from baseline over two consecutive measurements will provide the OCTT for each subject after conversion to minutes.

In order to evaluate the impact of Ramadan, parameters related to glycemia, triglycerides, and cholesterol will be evaluated by a blood test. Fecal microbiota analysis will be conducted at DISSPA (Department of Soil, Plant, and Food Sciences).

Inclusion Criteria:

• Subjects able to provide informed consent
• Age between 20 and 60
• Healthy Volunteers

Exclusion Criteria:

• Lack of informed consent
• Diagnosis of organic diseases, including neoplastic inflammatory diseases or cardiovascular diseases
• Medications that can affect the gastrointestinal tract and interfere with symptoms
• Pregnancy
• Presence of diseases with a prognosis of less than 12 months
• Celiac disease

For this pilot study 21 subjects homogeneously distributed by sex, age and BMI will be involved. The subjects will be required to practice religious fasting (Ramadan fasting) for 29/30 days.