Intermittent fasting (IF) may offer benefits for losing weight, managing diabetes, improving athletic performance, and more. Some studies suggest blood pressure and heart health improvements, but more research is needed to understand these benefits.
Intermittent fastingis a way of eating that involves periods of fasting that alternate with eating windows. It is not the same as fasting for other reasons, such as having a blood test. Different methods vary in fasting periods and restrictions on what you can eat and drink.
PeopleImages / Getty Images
Why Do People Start Intermittent Fasting?
Aside from fasting for religious beliefs or cultural reasons, the most common health-related reason for fasting is for weight loss. For example, a 2022 study on intermittent fasting focused on people diagnosed with obesity or overweight who had co-occurringprediabetes(the stage beforetype 2 diabetes).
At the end of this clinical trial, people assigned to the intermittent fasting groups had greater reductions in body weight,body mass index (BMI), and waist circumference compared to the control group.The intermittent fasting groups also experienced significant decreases in bothblood glucose (sugar)andtriglyceride(a type of fat) levels.
A systematic review of 40 studies on intermittent fasting found that it helped people lose weight, with a typical weight loss of 7 to 11 pounds over 10 weeks.
BMI is a dated and flawed measure. It does not take into account factors such asbody composition, ethnicity, sex, race, and age. Even though it is abiased measure, BMI is still widely used in the medical community because it’s an inexpensive and quick way to analyze a person’s potential health status and outcomes.
Some studies have shown promising results for the health benefits of intermittent fasting beyond weight loss. The research includes:
Additional research and larger clinical trials are needed to determine whether intermittent fasting is beneficial in other ways and in the long term.
8 Proven Health Benefits of Fasting
What Is Metabolism?Metabolismrefers to all of the chemical processes or changes that occur in the body at the cellular level. These changes make energy and the materials organisms and cells need in order to grow, reproduce, and maintain life.In relation to diet, metabolism is the process of digesting or breaking down the food you eat into a simpler form the body is able to use. Metabolism is also involved when your body breaks down muscle or stored fat to be used as energy during periods of strenuous exercise or fasting.
What Is Metabolism?
Metabolismrefers to all of the chemical processes or changes that occur in the body at the cellular level. These changes make energy and the materials organisms and cells need in order to grow, reproduce, and maintain life.In relation to diet, metabolism is the process of digesting or breaking down the food you eat into a simpler form the body is able to use. Metabolism is also involved when your body breaks down muscle or stored fat to be used as energy during periods of strenuous exercise or fasting.
Metabolismrefers to all of the chemical processes or changes that occur in the body at the cellular level. These changes make energy and the materials organisms and cells need in order to grow, reproduce, and maintain life.
In relation to diet, metabolism is the process of digesting or breaking down the food you eat into a simpler form the body is able to use. Metabolism is also involved when your body breaks down muscle or stored fat to be used as energy during periods of strenuous exercise or fasting.
Methods
There are several different methods of intermittent fasting. They vary in their timing patterns and food intake restrictions. You can talk with your healthcare provider about options and the best schedule for intermittent fasting.
Time-Restricted (16:8 or 14:10) Intermittent Fasting
Time-restricted fasting is one of the most commonly used methods of IF, especially for beginners. This method follows a 16:8 schedule, in which you fast for 16 hours a day and have an eight-hour eating window.A modified version alternates 14-hour fasts with 10-hour eating windows.
Overnight (12:12) Intermittent Fasting
A shortened version of time-restricted fasting is to fast overnight for 12 hours. This method might be a good option for beginners, as most of the fasting window is while you’re sleeping.
Alternate Day Intermittent Fasting
Alternate day fasting involves fasting every other day.Being a more extreme method, this variation (sometimes called the 4:3 method) may not be appropriate for intermittent fasting beginners or people with certain medical conditions.
5:2 Intermittent Fasting
The 5:2 diet, also known as the Fast Diet, involves eating regularly five days a week and following a modified fast two days. This method is a little more flexible, as you are allowed to choose which days of the week are your modified fasting days.
How the Fast-Mimicking Diet Works
Warrior Diet (20:4) Intermittent Fasting
One Meal a Day (OMAD) Intermittent Fasting
Eat Stop Eat Intermittent Fasting
The Eat Stop Eat method involves fasting for 24 hours one or two nonconsecutive days a week. This method is similar to the 5:2 fasting diet. However, the 5:2 method allows for 500 to 600 calories on fasting days, while the Eat Stop Eat method does not.
Safety: Who Shouldn’t Try It
While intermittent fasting may be beneficial for someone trying to lose weight, it isn’t for everyone. Always talk with a healthcare provider before starting a new diet or eating pattern, especially if you have a known medical condition. It may be unsafe for:
In addition, a 2024 study of over 20,000 adults found that those who followed an eight-hour time-restricted eating schedule had a 91% higher risk of death from cardiovascular disease compared to people who ate across 12-16 hours per day. The study also found people with heart disease or cancer also had an increased risk of cardiovascular death.
Possible Risks in Males vs. FemalesA review of human trials found that fasting may reduce levels of androgens (reproductive and growth hormones), which can negatively impact metabolic health and libido (sexual desire) in males.Some studies suggest that females may be more sensitive to fasting, most likely due to fluctuating hormones or stress-related changes.More research is needed.
Possible Risks in Males vs. Females
A review of human trials found that fasting may reduce levels of androgens (reproductive and growth hormones), which can negatively impact metabolic health and libido (sexual desire) in males.Some studies suggest that females may be more sensitive to fasting, most likely due to fluctuating hormones or stress-related changes.More research is needed.
A review of human trials found that fasting may reduce levels of androgens (reproductive and growth hormones), which can negatively impact metabolic health and libido (sexual desire) in males.
Some studies suggest that females may be more sensitive to fasting, most likely due to fluctuating hormones or stress-related changes.More research is needed.
Summary
Intermittent fasting (IF) involves periods of fasting alternating with periods of eating. There are several methods of IF with variations in the amount of time spent fasting versus eating. Benefits may include weight loss, disease prevention or management, or improved metabolism, and brain health.
Talk with your healthcare provider about intermittent fasting. It can present risks to people with certain medical conditions like diabetes, or who take medications with food.
18 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Dong TA, Sandesara PB, Dhindsa DS, Mehta A, Arneson LC, Dollar AL,et al.Intermittent Fasting: A Heart Healthy Dietary Pattern?Am J Med. 2020 Aug;133(8):901-907. doi:10.1016/j.amjmed.2020.03.030
Vasim I, Majeed CN, DeBoer MD.Intermittent Fasting and Metabolic Health.Nutrients. 2022 Jan 31;14(3):631. doi:10.3390/nu14030631
Chair SY, Cai H, Cao X, Qin Y, Cheng HY, Ng MT.Intermittent fasting in weight loss and cardiometabolic risk reduction: a randomized controlled trial.J Nurs Res. 2022;30(1):e185. doi:10.1097/jnr.0000000000000469
Seimon RV, Roekenes JA, Zibellini J, et al.Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials.Mol Cell Endocrinol. 2015;418 Pt 2:153-172. doi:10.1016/j.mce.2015.09.014
Guo Y, Luo S, Ye Y, Yin S, Fan J, Xia M.Intermittent fasting improves cardiometabolic risk factors and alters gut microbiota in metabolic syndrome patients.J Clin Endocrinol Metab. 2021;106(1):64-79. doi:10.1210/clinem/dgaa644
National Psoriasis Foundation.Intermittent Fasting.
Barati M, Ghahremani A, Namdar Ahmadabad H.Intermittent fasting: A promising dietary intervention for autoimmune diseases.Autoimmun Rev. 2023 Oct;22(10):103408. doi:10.1016/j.autrev.2023.103408
Martínez-Rodríguez A, Rubio-Arias JA, García-De Frutos JM, Vicente-Martínez M, Gunnarsson TP.Effect of high-Intensity Interval training and Intermittent fasting on body composition and physical performance in active women.Int J Environ Res Public Health. 2021;18(12):6431. doi:10.3390/ijerph18126431
Moro T, Tinsley G, Bianco A, et al.Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males.J Transl Med. 2016;14(1):290. doi:10.1186/s12967-016-1044-0
Seidler K, Barrow M.Intermittent fasting and cognitive performance - Targeting BDNF as potential strategy to optimise brain health.Front Neuroendocrinol. 2022;65:100971. doi:10.1016/j.yfrne.2021.100971
Kim BH, Joo Y, Kim MS, Choe HK, Tong Q, Kwon O.Effects of Intermittent Fasting on the Circulating Levels and Circadian Rhythms of Hormones.Endocrinol Metab (Seoul). 2021 Aug;36(4):745-756. doi:10.3803/EnM.2021.405
Cui Y, Cai T, Zhou Z, Mu Y, Lu Y, Gao Z,et al.Health Effects of Alternate-Day Fasting in Adults: A Systematic Review and Meta-Analysis.Front Nutr. 2020 Nov 24;7:586036. doi:10.3389/fnut.2020.586036
Guo L, Xi Y, Jin W, Yuan H, Qin G, Chen S,et al.A 5:2 Intermittent Fasting Meal Replacement Diet and Glycemic Control for Adults With Diabetes: The EARLY Randomized Clinical Trial.JAMA Netw Open. 2024 Jun 3;7(6):e2416786. doi:10.1001/jamanetworkopen.2024.16786
Meessen ECE, Andresen H, van Barneveld T, et al.Differential effects of one meal per day in the evening on metabolic health and physical performance in lean individuals.Front Physiol. 2022;12:771944. doi:10.3389/fphys.2021.771944
American Heart Association.8-hour time-restricted eating linked to a 91% higher risk of cardiovascular death.
Cienfuegos S, Corapi S, Gabel K, et al.Effect of intermittent fasting on reproductive hormone levels in females and males: a review of human trials.Nutrients. 2022;14(11):2343. doi:10.3390/nu14112343
Solianik R, Sujeta A.Two-day fasting evokes stress, but does not affect mood, brain activity, cognitive, psychomotor, and motor performance in overweight women.Behav Brain Res. 2018;338:166-172. doi:10.1016/j.bbr.2017.10.028
Meet Our Medical Expert Board
Share Feedback
Was this page helpful?Thanks for your feedback!What is your feedback?OtherHelpfulReport an ErrorSubmit
Was this page helpful?
Thanks for your feedback!
What is your feedback?OtherHelpfulReport an ErrorSubmit
What is your feedback?
