Scientifically proven benefits of intermittent fasting include mild to moderate reductions in body weight, fat mass, and waist circumference, particularly in overweight or obese adults. Intermittent fasting regimens such as time-restricted eating (TRE), alternate-day fasting (ADF), and the 5:2 diet have demonstrated improvements in insulin sensitivity, reductions in fasting insulin and glycosylated hemoglobin, and favorable changes in lipid profiles (notably reductions in triglycerides and LDL cholesterol, and increases in HDL cholesterol).[1-4] Cardiometabolic risk factors such as blood pressure and markers of inflammation may also improve, with some evidence for decreased diastolic blood pressure and systemic inflammation.[2][4-5] In addition, intermittent fasting may benefit liver health in non-alcoholic fatty liver disease and improve appetite regulation and gut microbiome diversity, though evidence for these effects is less robust.[2-3]
Risks of intermittent fasting are generally mild in healthy adults. The most commonly reported adverse effects are transient headaches, hunger, and irritability, especially during the initial adaptation period.[6] There is no evidence of increased disordered eating behaviors or significant disturbances in energy levels in the short- to medium-term.[2][6] However, the long-term safety profile remains uncertain, particularly in specific populations such as those with diabetes, eating disorders, or older adults, as most studies have focused on overweight young and middle-aged adults and have not assessed outcomes beyond 6–12 months.[3][5-6] Clinical differences between intermittent fasting and continuous energy restriction are minor, and both approaches are comparably effective for weight loss and cardiometabolic improvements.[1][4][7]
In summary, intermittent fasting is a safe and effective dietary strategy for weight loss and metabolic health in overweight or obese adults, with mild and transient risks, but long-term effects and safety in other populations require further study.[1][3-4]
References
- Intermittent Fasting Strategies and Their Effects on Body Weight and Other Cardiometabolic Risk Factors: Systematic Review and Network Meta-Analysis of Randomised Clinical Trials. Semnani-Azad Z, Khan TA, Chiavaroli L, et al. BMJ (Clinical Research Ed.). 2025;389:e082007. doi:10.1136/bmj-2024-082007.
- Cardiometabolic Benefits of Intermittent Fasting. Varady KA, Cienfuegos S, Ezpeleta M, Gabel K. Annual Review of Nutrition. 2021;41:333-361. doi:10.1146/annurev-nutr-052020-041327.
- Intermittent Fasting for Weight Management and Metabolic Health: An Updated Comprehensive Umbrella Review of Health Outcomes. Hua Z, Yang S, Li J, et al. Diabetes, Obesity & Metabolism. 2025;27(2):920-932. doi:10.1111/dom.16092.
- Longer-Term Effects of Intermittent Fasting on Body Composition and Cardiometabolic Health in Adults With Overweight and Obesity: A Systematic Review and Meta-Analysis. Khalafi M, Maleki AH, Ehsanifar M, Symonds ME, Rosenkranz SK. Obesity Reviews : An Official Journal of the International Association for the Study of Obesity. 2025;26(2):e13855. doi:10.1111/obr.13855.
- Effects of Intermittent Fasting on Health, Aging, and Disease. de Cabo R, Mattson MP. The New England Journal of Medicine. 2019;381(26):2541-2551. doi:10.1056/NEJMra1905136.
- Intermittent Fasting for the Prevention of Cardiovascular Disease. Allaf M, Elghazaly H, Mohamed OG, et al. The Cochrane Database of Systematic Reviews. 2021;1:CD013496. doi:10.1002/14651858.CD013496.pub2.
- Effects of Intermittent Fasting on Cardiometabolic Health: An Energy Metabolism Perspective. Dote-Montero M, Sanchez-Delgado G, Ravussin E. Nutrients. 2022;14(3):489. doi:10.3390/nu14030489.