It has surged in popularity in recent years, thanks to the fitness and nutrition industry with claims that intermittent fasting can do everything from burn fat and build muscle to cleanse the body and boost longevity.
So does intermittent fasting work at achieving any (or all) of those claims?
Read on to get a breakdown of intermittent fasting, benefits,
What Is Intermittent Fasting?
“Intermittent fasting is an umbrella term for three different diets: alternate-day fasting (ADF), the 5:2 diet, and time-restricted eating (TRE),” explains Dr. Krista A. Varady, Ph.D., Professor of Nutrition at the University of Illinois Chicago and co-author of “The Every Other Day Diet.”
Varady has been researching alternate-day fasting for 15 years, authoring 70 papers on the subject.
Many IF plans have you stop eating for a certain amount of time, typically anywhere from 16 to 24 hours.
But other plans forgo abstinence in favor of reducing calories to a very low amount.
That’s the case with alternate-day fasting (ADF), which generally requires people to eat just 500 calories every other day.
Different Forms of Intermittent Fasting
As Varady explains, there are multiple forms of intermittent fasting. The most basic of these is time-restricted eating (TRE).
If you follow this form of fasting, you limit the amount of time you eat in a day to a certain number of hours.
Most people begin their fast after dinner so that they only have a couple of hours left to fast after they wake up.
Someone on a 16/8 fast, for example, could stop eating at 8pm and start eating again at noon the next day. Alternate-day fasting requires a low-calorie intake every other day. On the alternate days, you eat as you normally would.
The 5:2 diet, which is sometimes referred to as “The Fast Diet,” is a form of alternate-day fasting.
Following this form of IF requires you to restrict calories to 500-600 two days a week. The other five days of the week are regular eating days.
Benefits of Intermittent Fasting
First things first: There are a lot of purported health claims tied to intermittent fasting, but not all of these are rooted in science or verified at this point.
There are proven benefits to this style of eating, though. “[Research shows that] IF can help lower diabetes and heart disease risk,” Varady adds.
But you’ll have to give this new style of eating longer than a month to show these results.
Research has shown that “blood pressure, LDL cholesterol, triglycerides, fasting insulin, and insulin resistance all decrease after 6-8 weeks of IF combined with endurance exercise,” Varady explains.
But Krista Maguire, R.D., C.S.S.D., and Beachbody nutrition manager underscores that “just because you cut down the number of hours you’re actually eating food, doesn’t necessarily mean you’ve created a daily calorie deficit which is required to lose weight.”
So some calorie counting may still be required if you’re using a form of intermittent fasting as a weight-loss tool.
At the end of the day, the best weight-loss plan for you is the one you can stick to consistently and long-term.
How to Start Intermittent Fasting
“First of all, I’d recommend checking with your healthcare provider to make sure intermittent fasting is appropriate for you,” Maguire advises.
Once you have the green light from a medical professional, she suggests you “start with a version of IF that isn’t too drastic.”
That might even mean simply closing the kitchen after dinner and opening it again for breakfast if you’re used to snacking at night, Maguire adds.
Varady agrees, suggesting that people “start with a 10-hour [feeding] window for the first week, then move to 8-hour the second week.”
From there, you can shorten your feeding window weekly if you’re still feeling good.
Remember that you can start this window whenever it feels natural with your hunger cues.
If you wake up hungry, there’s no reason to skip breakfast. You can eat in the morning and start your fast in the afternoon.
Hunger pangs are natural for the first week or two of fasting; coffee, tea, unsweetened seltzers, or flavored water can help assuage those pangs and habitual snacking.
Part of the Diet for Weight Loss Editorial Team 2021