Before changing the way you eat and altering your diet in any significant way, please speak with a health professional to make sure it's the best decision for you.

An empty stomach is perfectly natural. Fasting is something we all do while we’re asleep and whenever we don’t have food in our mouths — you’re probably fasting right now. Due in part to a recent spate of and , “intermittent fasting” (or “IF,” typically defined as consuming nothing but water for 16 to 36 hours) has gained tremendous popularity in health and fitness circles as a way to lose fat, live longer, and even build muscle.

But taking a break from food can be incredibly controversial, particularly among those who are still sold on the old doctrine of eating . So how could IF be one of the simplest and safest tools for managing your health?

What’s the Deal?

We’ve gone over this before, but to refresh: The human metabolism does not grind to a halt if you skip a meal (or three). For it to slow down by even ten percent, one would need to fast for 72 hours straight (don’t worry, no one’s recommending giving up food for three days) . Cameron JD, Cyr, MJ, et al. Behavioural and Metabolic Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada. British Journal of Nutrition, 2010 Apr;103(8):1098-101. . Zauner C, Schneeweiss B, et al. Intensive Care Unit, the Department of Internal Medicine IV, University of Vienna, Vienna, Austria. American Journal of Clinical Nutrition, 2000 Jun;71(6):1511-5. . Nair KS, Woolf PD, et al. Department of Medicine, University of Rochester School of Medicine and Dentistry, NY, USA. American Journal of Clinical Nutrition, 1987 Oct;46(4):557-62. . Klein S, Holland OB, et al. Department of Internal Medicine, University of Texas Medical Branch, Galveston, TX, USA. American Journal of Physiology, 1990 Jan;258(1 Pt 1):E32-9.. In fact, even 48 hour fasts have been shown to have no negative effect on metabolism, cognitive performance, or fatigue . Lieberman HR, Caruso CM, et al. Military Nutrition Division, US Army Research Institute of Environmental Medicine, Natick, MA, USA. American Journal of Clinical Nutrition, 2008 Sep;88(3):667-76. . Green, MW, Elliman NA, et al. Consumer Sciences Department, Institute of Food Research, Reading, U.K. Journal of Psychiatric Research, 1995 May-Jun;29(3):245-53.. That’s not to say fasting can’t be a little uncomfortable — we’ll get to that later.

But why would anybody want to fast? For starters, IF shares many of the benefits of following a low calorie diet, such as a lower risk of stroke and . Bales CW, Kraus WE. Division of Geriatrics, Department of Medicine, Duke University Medical Center, Durham, NC, USA. Journal of Cardiopulmonary Rehabilitation and Prevention, 2013 Jul-Aug;33(4):201-8. . Mattson MP, Wan R. Laboratory of Neurosciences, National Institute on Aging Intramural Research Program, Baltimore, MD, USA. The Journal of Nutritional Biochemistry, 2005 Mar;16(3):129-37. . Varady KA, Hellerstein MK. Department of Nutritional Sciences and Toxicology, University of California at Berkeley, Berkeley, CA, USA. American Journal of Clinical Nutrition, 2007 Jul;86(1):7-13.. Fasting’s effect on the heart is especially interesting: One study concluded just one day without food per month can potentially of developing coronary artery disease . Horne BD, May HT, et al. Cardiovascular Department, Intermountain Medical Center, Murray, Utah, USA. American Journal of Cardiology, 2008 Oct 1;102(7):814-819..

But there’s another effect of periodic fasting that both of chronic disease and improves the body’s digestion of carbohydrates (as in, they become less likely to make you fat). It’s all about insulin, a hormone responsible for the uptake of nutrients into the liver, muscles, and fat cells. Because the body releases insulin when carbohydrates are consumed, eating too much and too often can make us less sensitive to it. (Makes sense, right?) Unfortunately, an abundance of food (as well as other factors, like and exercise) has made poor insulin sensitivity fairly commonplace . Halberg N, Henriksen M, et al. Dept. of Muscle Research Centre, The Panum Institute, University of Copenhagen, Denmark. Journal of Applied Physiology, 2005 Dec;99(6):2128-36.. That’s bad. Not just because it makes it more difficult to lose fat and , but also because it increases the risk of diabetes and several kinds of cancer . Stolzenberg-Solomon RZ, Graubard BI, et al. National Cancer Institute, Department of Health and Human Services, Rockville, MD, USA. Journal of the American Medical Association, 2005 Dec 14;294(22):2872-8. . De Nunzio C, Aronson W, et al. Department of Urology, Sant'Andrea Hospital, University La Sapienza, Rome, Italy. European Urology, 2012 Mar;61(3):560-70. . Bruning PF, Bonfrèr JM, et al. The Netherlands Cancer Institute, Amsterdam, The Netherlands. Bruning PF, Bonfrèr JM, et al. The Netherlands Cancer Institute, Amsterdam, The Netherlands. International Journal of Cancer, 1992 Oct 21;52(4):511-6.. Fortunately, the problem can be improved by essentially doing nothing — not eating increases insulin sensitivity, meaning regular fasts allow you to eat more carbs, get less sick, and burn more fat . Halberg N, Henriksen M, et al. Dept. of Muscle Research Centre, The Panum Institute, University of Copenhagen, Denmark. Journal of Applied Physiology, 2005 Dec;99(6):2128-36. . Horne BD, May HT, et al. Cardiovascular Department, Intermountain Medical Center, Murray, Utah, USA. American Journal of Cardiology, 2008 Oct 1;102(7):814-819..

Twenty-four hour fasts have also been the brain’s production of growth hormone by up to 2,000 percent in men and 1,300 percent in women (the effect ends when the fast does). This is good news for anybody looking to slow the aging process: Growth hormone isn’t just awesome at lowering body fat while preserving muscle (weightlifters, rejoice!) but it improves physical function, bone quality, and . Clemmons D. Nature Reviews Endocrinology, 2013 Jun;9(6):317-8. . Reed ML, Merriam GR. Geriatrics and Extended Care, VA Puget Sound Health Care System, Madigan Health Care System, Tacoma, WA, USA. Frontiers in Endocrinology (Lausanne), 2013 Jun 4;4:64. . Miller GD, Nicklas BJ, et al. Department Health and Exercise Science, Wake Forest University, Winston-Salem, NC, USA. The Journal of Nutrition Health and Aging, 2012 Feb;16(2):169-74..

So Fasting Affects Men and Women Differently?

, but exactly why or how much is still a point of debate. While there are some assertions that to the stress of going without food, with it. More research is needed, but it’s important to remember that as with all diets, IF works for some people and doesn’t for others. Feel it out and see what works for you.

Won’t I Get Hungry?

We hear ya. While on a fast, it’s a good idea to drink plenty of water, plain tea, black coffee, and other very low-calorie drinks to keep the stomach from feeling too empty — isn’t considered . But it might relax you to know the initial hunger probably isn’t because the body requires food, but because of a hormone called ghrelin.

Ghrelin is an appetite stimulant the body learns to secrete based off your , so it makes you hungry when you would normally be eating. (This has earned it the nickname, “.”) That’s why eating throughout the day , and it can also make IF uncomfortable at first . Leidy HJ, Armstrong CL, et al. Department of Dietetics & Nutrition, University of Kansas Medical Center, Kansas City, Kansas, USA. Obesity (Silver Spring). 2010 Sep;18(9):1725-32.. After a few fasts, however, the body learns to produce less ghrelin, and over when you eat.

But those first few fasts can be jarring, and for some, struggling with ghrelin is not worth the adaptation period — and that’s fine! Eating is personal, and if the discomfort is severe, there’s no obligation to continue. The takeaway here is that you have more control over when you eat than you might think. Like most things, it just takes a little practice.

So Should I Try It Out?

The science behind IF is pretty solid, but that doesn’t mean it’s the only path to better health. If fighting through ghrelin surges or skipping meals with loved ones become insurmountable problems — or if you’re , diabetic, or have a history of eating disorders — IF might be worth avoiding. As always, it’s wise to speak with a physician before changing the way you eat.

It’s also important to remember that no matter when we eat, what and how much we eat is always important — the improved hormones and smaller eating windows of IF are not a carte blanche to consume thousands of extra calories!

Of course, ideas about exactly when to eat and when to fast can vary from one person to the next. There are many : Some swear by a , and others prefer once or twice a week. Keep track of how you feel, and again, if the fast is too hard, just break it. Try again another time, perhaps after a particularly big meal. If it’s unbearable, stop bearing it. While a heightened awareness of food intake is a great side effect, the best part of intermittent fasting — at least — is the flexibility and simplicity it brings to the eating process. Eat when hungry, don’t when not. Six meals per day or one big dinner, the research shows that you can eat when you feel like eating. The metabolism won’t shut down, muscles won’t atrophy, and the sun will rise in the morning. It takes a load off, don’t it?

There’s no harm in giving it a try. Intermittent fasting is rapidly becoming a popular and powerful method for fighting disease, improving body composition, and taking some of the stress out of dieting and meal planning, but remember: if it doesn’t work for you, it’s not the only way to get results.

Special thanks to , founder of , for his help with this article.

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