Find out what’s behind this on-/off-approach to eating, whether you should try it, and how it works.
Intermittent fasting is a cycle of eating (and not eating). It involves restricting when you consume food, either by rotating between low-calorie and normal diet days, or by eating only during a specific window of time.
Intentional fasting is an age-old practice. Many major religions, including Buddhism, Christianity, Judaism, and Islam include it. Muslims, for example, fast from dawn to dusk during Ramadan.
Of course, this is not to be confused with prolonged fasting (aka starvation), which results in degeneration and death; or calorie restriction, a diet approach that restricts the amount of food, rather than the frequency of consumption.
Think about it: Every night, when you sleep and/or don’t raid the fridge past midnight, your body fasts. Between your last meal one day and the first meal the next day, then, our body experiences a non-eating phase.
Comprehensive medical (human) research on this approach is not (yet) widely available. But some studies have found that fasting leads to lower blood sugar, decreased blood pressure, and healthier cholesterol levels. It’s possible that fasting can even reduce your risk of heart disease.
Plant and animal studies have found interesting results from intermittent fasting, including reprogramming of metabolic and stress reactions, as well as protecting against diabetes and other conditions. What’s more, fasting has been shown to increase human growth hormone — a recovery-inducing peptide hormone that stimulates cell reproduction — in men.
Generally, this style of eating results in consuming fewer calories than you would on a “normal” eating schedule, so folks may see weight-loss results off the bat!
On Ben Greenfield’s podcast, Dr. Jason Fung — a nephrologist and chief of the department of medicine Scarborough General Hospital in Toronto, Canada — explains what happens when you fast:
As the food you recently ate is used for energy, your insulin (a hormone) falls, and your body turns to glycogen stores for energy. It burns glucose for up to about 24 hours. Then, gluconeogenesis sets in — a process where your body creates glucose from protein — to feed cells. At this point, your body also increases fat oxidation, which is more difficult than using glycogen. After 36 hours, he says, fat oxidation takes over. Fatty acid levels in the blood increase, as your body is gleaning stored fat for energy. Technically, that phase is called ketosis.
This does NOT mean you should not eat for 36 hours. Rather, this paints a picture of what, physiologically, happens to your body during fasting. With IF and other forms of so-called “hacking” your daily diet, various methods short-cut these processes and teach your body to tap into stored energy sources.
Most importantly, it’s good to know how many systems inside your body are at play!
It’s also a reminder to seek advice of a medical professional if you have any questions or concerns.
Advocates say perks of IF include:
- Weight loss: In line with early studies.
- Resolve: Some prefer restricting eating to a specified time period, rather than having to control or moderate eating all day long.
- Simplicity: Not eating, for example, four times a day, means saving time otherwise required for planning, preparation, and cleaning (and/or money, if you eat out). Let’s be honest: No one wants to do the dishes!
Here are a few examples of intermittent fasting schedules:
- 16/8: Eat in an 8-hour window, fast for 16.
- Eat-Stop-Eat: Fast for 24 hours. For example, eat dinner one night and abstain from food until dinner the following day.
- 5:2: During one week, chose two days during which you only eat about 500 calories. See more IF methods here.
A Few Frequently Asked Questions about Intermittent Fasting:
Q.I thought missing meals, like breakfast, was bad for my metabolism. Won’t I, like, die if I skip a meal or three?
A. Nope. Worst case scenario, at first, you feel a little hungry, or get kind of cranky. According to IF expert and doctor Dr. Fung, in fact, fasting is better for your metabolism than, say, Biggest Loser-type, move-more/eat-less approaches, which can lower and stall your basal metabolic rate. Plus, thanks to the so-called hunger hormone ghrelin, the sensation of hungry won’t actually build and build — it will pass as your body adapts to using stored energy for fuel.
Q. Is this a good diet for people with disordered eating or eating disorders?
A. Maybe not. If you have a history of restricting and/or binging, check in with your healthcare provider and a registered dietician before starting an IF protol.
Q. How do athletes fuel and refuel enough?
A. Again, each person is different and should keep their activity levels and individual needs in mind before embarking on a new eating program. That said, athletes who use intermittent fasting fit in their nutritional needs when they do eat — for example, between noon and 8 pm. With thoughtful timing of activities and exercise, active and competitive athletes can tailor their training, competition, and nutrition for optimum performance.