Find out how it stacks up to simply cutting calories.
It involves set times when your eating is restricted and others when you eat as normal—or even more than you would typically.
But is there really any benefit to this kind of eating? A new study adds some clarity to the complicated topic: Intermittent fasting is no more effective for weight loss than daily calorie restriction, researchers from the University of Illinois at Chicago report.
Researchers split 100 inactive, overweight men and women with no history of heart disease or diabetes into three groups: A calorie-restricted group, an alternate-day fasting group, and a control group.
The calorie-restricted group took the traditional weight loss approach. Every day, they reduced their caloric intake by 25 percent, meaning they ate 75 percent of the calories they would need to maintain their weight among three meals a day.
The alternate-day fasting group ate 25 percent of their caloric needs every other day, known as “fast” days, between 12 p.m. and 2 p.m. They bookended their “fast” days with “feast” days, when they ate 125 percent of their caloric needs among three meals a day. So if you typically eat 2,000 calories a day, you’d eat 500 calories one day, followed by 2,500 the next. (Find out how many calories you need here.)
People in the control group ate as they normally would, but were instructed to maintain their weight throughout the study.
After 6 months, the study participants were told to maintain their weight loss for another 6 months. During this phase, the fasting group ate half their caloric needs on fast days and 150 percent on feast days, while the calorie-restricting group ate 100 percent of what they needed every day.
After one year, there was no significant difference in how much weight either weight-loss group lost or how long they kept it off, the study found. What’s more, neither group experienced any higher risk for other health issues, like cardiovascular disease.
The success of any weight loss plan depends on whether you’ll actually stick with it long enough to see results. So, which one is more sustainable?
In the study, 38 percent of people dropped out of the fasting group compared to 29 percent of people in the calorie-restricting group by the end of the year. And over time, people in the fasting group started moving toward daily calorie restriction, potentially signaling that it could be hard to stick with in the long run, the study authors say.
But that might simply have to do with how the study was set up: The researchers broke down the diets into 30 percent fat, 55 percent carbs, and 15 percent protein. Eating only 15 percent of your calories from protein—especially on fast days, when you’re eating so little overall—can make you feel hungrier, making the plan harder to stick to, says obesity specialist Spencer Nadolsky, D.O.
If hunger becomes an issue on “fast” days, bumping up your protein intake helps keep you fuller for longer, possibly boosting your ability to adhere to the diet, he says.
So if both methods help you lose weight, how do you know which one will work best for you?
“The people who can benefit from this type of alternate-day fasting are those who would rather feel like they aren’t restricting food intake 3.5 days out of the week,” says Men’s Health nutrition advisor, Alan Aragon, M.S. Meaning, you find it hard to stick to a diet all the time, and you like the “break” of feast days.
But on the other hand, the intense restriction intermittent fasting requires on the other days could be extremely difficult for some people, especially in certain instances.
Take your job, for example: If your day-to-day work requires hard, manual labor, fasting may not work for you, since you’re constantly burning energy, says Dr. Nadolsky. But if you have a desk job and your schedule doesn’t get in the way, 500-calorie days can be more realistic, he explains.
Bottom line: If you want to try intermittent fasting for weight loss—and your doctor okays it if you have any pre-existing health issues—you can give it a shot to see if it works for you.
So how can you make it more sustainable? Making less rules for yourself—like avoiding a specific caloric goal on feast days as they did in the study—may lead to better results, Aragon says. (If you want to maximize your results, check out MetaShred Extreme from Men’s Health, a fat-burning workout you can do right in your own living room.)
In fact, recent research shows that eating nothing on fasting days and as you normally would on feasting days may actually work better than daily-calorie restriction, Aragon notes.
Just keep in mind that most diets should lead to weight loss within a couple of months, Dr. Nadolsky says. So if you haven’t lost 2 percent of your weight in the first month or 3 percent by the second month, it may be worth looking into another approach or modifying the diet you’re currently on.