Nutrition experts used to debate whether you should eat three big meals or five little ones per day. (Okay, maybe they’re still debating it…) But another foodie fight has recently stolen the spotlight: fasting. As in eating just one meal per day on some days—if that.
Known as intermittent fasting (IF), this eating approach generally involves going anywhere from 14 to 36 hours at a time without eating. Essentially, you’re tricking your body into thinking you’re starving in an effort to slash calories and get your hormones in check.
Sound like fun? This seemingly torturous dieting style has seen serious traction—here’s what you need to know about its potential perks and whether or not it might work for you.
How It Works
Proponents of intermittent fasting believe the eating style shifts your body into ‘starvation mode,’ causing your metabolism to burn body fat for energy because energy from food is unavailable.
Related: 5 Myths About Your Metabolism—Busted
One of the most popular intermittent fasting protocols is the 5:2 Diet, which involves eating only 500 to 600 calories on two non-consecutive days per week. (You eat normally the other five.) The Eat Stop Eat method requires eating zero food (you can have calorie-free beverages) for a full 24 hours once or twice per week, and eating normally the rest of the time. Meanwhile, on the Warrior Diet, people fast every morning and afternoon and eat one large meal at night. Other methods include restricting food intake to four, six, or eight-hour windows each day.
A quick note for all of our gym-goers and exercise-lovers: On fasting or low-calorie days, workouts are off the table, as sweating it out on empty stomach can result in dizziness or fainting, not to mention poor workout quality.
The Possible Pros
The ultimate goal, for most people: weight loss. Much of the diet is centered on the all-important concept of caloric balance. Consume fewer calories than you burn, and, hypothetically, you’ll lose weight. And, for some people, it’s easier (or more appealing) to cut calories by skipping meals than by trimming calories at every meal, explains Luigi Fontana, M.D., Ph.D., a research professor of medicine at Washington University School of Medicine in St. Louis.
According to Fontana, intermittent fasting can reduce weekly caloric intake by 20 to 25 percent. Proponents of IF note that, in theory, even if you eat normally (or end up slightly overeating) on your regular eating days, eating minimally the rest of the time results in a caloric deficit.
Weight loss aside, some experts believe IF may hold further hormonal and health benefits. For instance, in one small University of Copenhagen study, men who followed an intermittent fasting protocol improved their bodies’ glucose-uptake rates, a measure of insulin sensitivity. (A decline in insulin sensitivity is often a precursor of diabetes.)
But There’s A Catch
But even if intermittent fasting may deliver on some health fronts, is it really any better than the more conventional strategy of cutting calories on a daily basis? So far, it doesn’t seem like it. For instance, one 2014 Translational Research review concluded that IF improves visceral (belly) fat and insulin resistance similarly to a daily calorie-cutting strategy. Plus, it also found conventional dieting to support total weight loss over time better than an intermittent fasting approach.
What’s more, IF may actually contribute to muscle-wasting and lowered metabolic rates over time—both of which are counterproductive to long-term weight loss and health. For example, one Pennington Biomedical Research Center study found that when men and women fasted every other day for 22 days, their resting metabolic rates dropped five percent.
Is It Worth Trying?
People interested in intermittent fasting should talk to their doctor before taking up the diet, Fontana says. Women who are pregnant or breastfeeding, and people recovering from an illness or surgery should not attempt intermittent fasting, since their bodies demand a pretty constant stream of nutrients.
Most health experts’ main concern with IF is that it can promote an unhealthy relationship with food. “Intermittent fasting does not allow a person to rely on his or her own hunger and satiety cues, but gives that ‘job’ to an artificial time clock,” says Kimberly Gomer, M.S., R.D., L.D.N. This may be especially problematic for those with a history of disordered eating. “Those with a prior history of compulsive or binge eating, as well as anorexia, can be at risk for these behaviors to be exacerbated by fasting,” explains Gomer.
Make Meal-Timing Work For You
Instead of following a strict eating protocol like intermittent fasting, experts recommend taking a more intuitive, mindful approach to eating.
Gomer suggests eating small meals throughout the day, starting when you feel slightly hungry and putting the fork down when you’re slightly satisfied. (Keep in mind it takes about 15 to 20 minutes for the body to fully register fullness.)
Another tip? To improve your ability to tap into your bod’s signals, work on nixing distracted eating. According to research published in the American Journal of Clinical Nutrition, multitasking during your meals—whether it’s watching TV to walking down the street—can reduce your brain’s ability to gauge food intake and lead to overeating.