During the month of Ramadan, Muslims worldwide fast from dawn to sunset, abstaining from food, drink, and other physical needs. Dr. Sherif Hassan, a professor of internal medicine at the UC Riverside School of Medicine, addressed common questions about the health impacts and safety considerations related to Ramadan fasting.
Dr. Hassan explained that “Fasting during Ramadan is physiologically similar to time-restricted eating, as both shift the body from glucose to fat use after 12–16 hours. The key difference is that Ramadan prohibits fluids during daylight hours, increasing dehydration risk. Sleep pattern changes during Ramadan can also influence metabolic outcomes.”
He noted that after about 12–16 hours without food, “After glycogen stores decline, insulin falls and the body increases fat breakdown and mild ketone production. Growth hormones rise and insulin sensitivity may improve temporarily. Energy shifts from glucose dependence to greater fat utilization.”
Regarding metabolic health benefits such as blood sugar and cholesterol levels, Dr. Hassan stated: “Short-term improvements in glucose, insulin sensitivity, triglycerides, and HDL are commonly observed. Effects depend heavily on diet quality and calorie intake during eating windows. Benefits often reverse if prior eating habits resume.”
When asked if there are differences in how men and women experience these effects, he said: “Women may be more hormonally sensitive to prolonged calorie restriction, particularly if underweight or stressed. Some may experience menstrual irregularities with aggressive fasting. Healthy men and women generally tolerate Ramadan well, but individual variability is significant.”
For people with type 2 diabetes considering fasting during Ramadan, Dr. Hassan advised caution: “People with type 2 diabetes can fast safely only if well controlled and medically supervised. Medication timing must be adjusted and glucose monitored closely. High-risk patients (those with poor diabetes control, insulin dependence, or kidney disease) are usually advised not to fast.”
On cardiovascular health effects he remarked: “Modest reductions in blood pressure and improvements in lipid markers are often seen. Weight loss and improved insulin sensitivity likely drive these effects. Dehydration, however, can cause dizziness or blood pressure fluctuations.”
As for weight loss expectations during Ramadan fasting: “Weight loss during Ramadan is typically modest and often temporary. Long-term success depends on sustained calorie control and healthy food choices. Fasting itself is a tool, not a guarantee of fat loss.”
Addressing risks for those with heart conditions: “Stable cardiac patients may fast safely with physician guidance. Those with advanced heart failure, unstable angina, or significant arrhythmias face higher risks from dehydration and electrolyte imbalance. Individual risk assessment is essential.”
On mental clarity while fasting he noted: “Some people report improved alertness due to mild ketosis and catecholamine increases. Others experience fatigue or reduced concentration, especially with dehydration or poor sleep. Cognitive response varies widely by individual.”
Regarding exercise safety during fasting periods: “Light to moderate exercise is generally safe, especially near or after breaking the fast. Intense training during prolonged dehydration increases risk of heat illness and fatigue. Athletes should optimize nighttime hydration and adjust training loads.”
Pregnant or breastfeeding women are advised caution according to Dr Hassan: “Pregnant women are generally advised not to fast. Breastfeeding may be affected by hydration and calorie intake.” He added that frail elderly individuals also face higher risks including dehydration.
Certain groups should avoid fasting altogether unless cleared by a doctor: “Those with uncontrolled diabetes, advanced kidney or heart disease, severe liver disease, eating disorders or acute illness should not fast without medical clearance,” he said.
On long-term health outcomes linked specifically to Ramadan fasting alone Dr Hassan commented: “Evidence shows short-term metabolic improvements but limited proof of lasting change without continued lifestyle modification.” He added there is no strong evidence suggesting harm in healthy adults.
He concluded that some groups benefit more than others: “Overweight individuals and those with mild insulin resistance often see the most metabolic improvement… Lean metabolically healthy individuals may see minimal measurable change.”
