Many Muslims worldwide are observing Ramadan, a month marked by fasting from dawn to sunset. During this period, participants abstain from food, drink, and other physical needs as part of religious practice and self-discipline.
Dr. Sherif Hassan, professor of internal medicine at the UC Riverside School of Medicine, provided insights into the physiological effects and medical considerations of Ramadan fasting. Dr. Hassan has an extensive background in medical education and clinical training.
He 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.”
On what happens in the body during a fast lasting 12–16 hours or more, Dr. Hassan said: “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.”
Short-term health improvements are often seen with fasting. According to Dr. Hassan: “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.”
Addressing gender differences in response to fasting, he noted: “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.”
Fasting can have some cardiovascular benefits but also risks: “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,” he said.
Regarding weight loss through fasting during Ramadan: “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.”
People with heart conditions should consult their doctors before fasting: “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,” according to Dr. Hassan.
Some individuals report mental clarity while fasting; others do not: “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,” he said.
Exercise while fasting requires moderation: “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,” Dr. Hassan stated.
Special populations such as pregnant women or elderly individuals face additional risks: “Pregnant women are generally advised not to fast. Breastfeeding may be affected by hydration and calorie intake. Frail elderly individuals are at higher risk of dehydration, falls, and kidney stress,” he explained.
Dr. Hassan emphasized that certain groups should avoid fasting without medical clearance: “Those with uncontrolled diabetes, advanced kidney or heart disease, severe liver disease, eating disorders, or acute illness should not fast without medical clearance. High risk of hypoglycemia or dehydration is a major contraindication.” He added that for these groups “medical harm outweighs potential benefits.”
On long-term health effects of Ramadan fasting based on current research findings: “Evidence shows short-term metabolic improvements but limited proof of lasting change without continued lifestyle modification. No strong evidence suggests harm in healthy adults.” He concluded that “long-term benefits depend on sustained healthy behaviors.”
Finally Dr.Hassan pointed out which groups might benefit most from this practice: “Overweight individuals and those with mild insulin resistance often see the most metabolic improvement.People who improve diet quality during Ramadan benefit more than those who overconsume high-calorie foods.Lean metabolically healthy individuals may see minimal measurable change.”
