Fasting during the month of Ramadan is considered one of the five pillars of the Islamic religion, and Muslims must abstain from eating and drinking between dusk and dawn. Research has found that fasting during Ramadan affects the health of Muslims but study results were often contradictory about the direction of those effects. Therefore this study aimed to determine whether a modified fasting regimen is beneficial for physical and mental health among adult Muslims undergoing Ramadan fasting. A randomized controlled trial with healthy adult Muslims aged 18 to 60 years was conducted during 2016 Ramadan. Two parallel groups were compared: the control group underwent the Ramadan fasting regimen as usual, while the experimental group received an educational booklet which contained information about the background of Ramadan, the influence of fasting on physical and mental health, and potential behavioural and nutritional modifications that might be benefit their health and well-being during Ramadan. Before, at the end of the Ramadan period, and 12 weeks later data were collected on participants mental and physical well-being, including wellbeing (WHO-5, primary outcome), sleep quality, spirituality, mindfulness, body constitution (weight, BMI, body fat, waist circumference, hip circumference), blood pressure and heart rate, serum marker (only baseline and post-intervention; incl. lipid and glucose levels, liver enzymes, uric acid and creatinine), and adverse events. 112 participants (63f, 49m; 27.8±9.4yrs) were randomised, and no drop-outs occurred. After Ramadan, the experimental group reported significant higher wellbeing (WHO-5, MD 5.93; 95% CI: 0.02 to 11.84), with 57.8% and 42.2% of participants in experimental and control groups being responders, respectively. Analyses revealed further group differences regarding satisfaction with life, and mindfulness, weight, BMI, hip circumference, and blood pressure directly after the intervention; however no group differences were found for serum markers. About 60% of participants reported adverse events, including headaches, dizziness, and gastrointestinal symptoms. Creatinine was elevated in two participants. Two serious adverse events occurred, but they were not intervention-related. A modified Ramadan fasting regimen appears to improve mental and physical health of Muslims; though observed effects were rather small and short-term only. Since the major limitation of this trial is the overrepresentation of young and healthy Muslims, further research is warranted to examine the effects of similar interventions in a sample of adults with diagnosed CVD risk factors.