Ramadan: A model for studying the effects of restricted time feeding on metabolic parameters and body composition in humans

Subjects will be studied on six occasions: (i) twice in the week before Ramadan (i.e. while maintaining their normal eating patterns), (ii) twice during the last week of Ramadan (while fasting from dawn to sunset), and (iii) twice 2 weeks after the end of Ramadan (i.e. following return to their normal eating patterns). Prior to their enrolment in the study, subjects will attend the hospital for a screening visit, where they will complete questionnaires to assess their medical history, and will provide written, informed consent. They will be provided with a food diary in which they will be required to record all of the food that they eat for a period of 3 days (2 weekdays and 1 weekend day) prior to their first study visit. They will also be instructed to record the time at which they eat. In the week before Ramadan, each subject will attend the hospital on two occasions. Diabetic subjects will be instructed to abstain from taking their medications on the day of the study visits. On the first visit, subjects will attend the Boden Institute of Obesity, Nutrition, Exercise & Eating Disorders at 12 pm, following a 5 hour fast from 7 am, where resting energy expenditure and respiratory quotient will be measured by indirect calorimetry for 60 minutes. Anthropometry (body weight, waist circumference) and body composition (by DEXA) will also be determined. On the second visit, participants with attend the RPAH between 5-6.30 pm, following a 10 hour fast from 7 am. On arrival, subjects will be seated comfortably and an intravenous cannula will be positioned into an antecubital vein of the arm to enable repeated blood sampling. Baseline blood samples will be collected to measure metabolic parameters, including a full blood count, glucose, HBA1C, lipids, liver function tests, insulin, c-peptide, thyroid function and FFAs, and for assessment of appetite regulating hormones (including gut derived appetite regulating hormones such as ghrelin, insulin, GLP-1, pYY and CCK, and leptin). Participants will also be asked to complete a visual analogue scale (VAS) questionnaire to assess perceptions of appetite and gastrointestinal symptoms. Following baseline assessments, participants will ingest a standardised meal (energy, macronutrient composition. Following meal ingestion, blood samples will be collected, and VAS completed, at 15, 30, 45, 60, 90 and 120 minutes. The participants will not be given any special instruction about their dietary intake during Ramadan. In the last week of Ramadan and at two weeks after Ramadan each participant will record their food intake for 3-days (2 weekdays and 1 weekend day) using a food diary, and will attend the laboratory on two days when the measurements described above will be repeated.