If you haven't met someone who's into intermittent fasting (IF), that's likely to change pretty soon. People who swear by IF say this diet trend has helped them lose weight and accelerate fat loss, gain muscle, and feel healthier overall. Although the idea behind this controversial eating plan isn't exactly a new one—it was used in the early 1900s to treat disorders such as diabetes and epilepsy—it's been gaining traction with modern-day dieters since The Fast Diet (aka the 5:2 program) was first published in 2013. So what is intermittent fasting—and should you join those who already swear by this practice for weight loss and other health benefits?
What is intermittent fasting?
There are now various versions of intermittent fasting, but the overarching concept is the same: Eat pretty much whatever you want, but only during a specific time period. Here are a few common iterations:
- The 5:2 program: Eat normally five days of the week; then, follow a modified fast for two days by eating very little, just 500-600 calories
- Leangains: Eat only within an 8- to 10-hour period each day and fast entirely for the remaining 14 to 16 hours
- Eat Stop Eat: Fast for a full day one to two days a week, and eat normally the other five or six days a week
- The Warrior Diet: Fast for 20 hours a day and eat one large meal every night
What are the benefits of intermittent fasting?
IF might sound wacky to some, but there’s evidence that they work. One study, published in the Journal of Translational Medicine in 2016, found that people who practiced IF for eight weeks lost more body fat than those in the control group. There may also be benefits beyond weight loss: A 2007 study in the American Journal of Clinical Nutrition concluded this dietary approach might help prevent chronic ailments like heart disease and type 2 diabetes.
“The majority of studies have been on animals, and we need more research,” says Robin Foroutan, RDN, a spokesperson for the Academy of Nutrition and Dietetics. "But if you're in overall good health, it's probably safe to try it out."
Lisa Jubilee, CDN, co-founder of Living Proof Pilates in New York City, who follows time-restricted eating herself, believes that IF has multiple benefits for many people, though there are specific groups who should steer clear or work closely with a doctor. How to know which camp you fall into? When in doubt, it's always smart to consult your personal doctor or nutritionist. But here are some indicators to help you sort it out.
Who's most likely to see results from intermittent fasting?
This eating plan might be worth a try if...
You’re an all-or-nothing kind of person.
If you've ever tried to diet, you likely know how it feels when you inevitably fall off the wagon. While some people can get right back on, others end up way off-course. "If you're not perfect and overindulge on dessert, you might think 'OK, I screwed up; now I'm going to go home and eat that bag of ginger snaps my kids left in the cabinet,'" says Jubilee. IF prevents you from going down that rabbit hole, because you're never worrying about what you're actually "allowed" to eat; instead, you just concentrate on sticking to your fast schedule. (See why it's good to occasionally take a break from your diet.)
You're always hungry.
Whether you're a speedy eater who overeats before your brain gets the message that you're full or you just never seem to be satisfied, IF might help. “When you're not eating all the time, your hunger hormones don't need to be released that often,” says Jubilee. “The body gets in a better hormonal balance, which enables you to get a grasp on your appetite.”
You want an inside-out anti-aging boost.
No, it's not a cure-all for creaky joints, wrinkled skin, or brittle hair, but IF prompts an increase in human growth hormone (HGH), which promotes cellular repair, says Foroutan. She explains that not eating for several consecutive hours creates a slight stress on your cells' mitochondria (the energy powerhouses), which gives them a nudge to rev up their functioning. IF might also be helpful for brain health; animal studies suggest that this eating pattern might serve to ward off age-related cognitive decline. (Check out whatthe perfect day of eating for brain health looks like.)
If your doctor has told you that you're in danger of developing diabetes, ask him or her if IF is worth a try. This type of eating plan may help your cells become more sensitive to insulin, says Foroutan. The reason: Every time you eat, your body releases the hormone insulin in an attempt to shuttle sugar from your bloodstream into your cells for energy. But people who are prediabetic are insulin resistant, which means that system no longer works properly and your blood sugar levels stay elevated. Going longer between eating may help because it requires your body to pump out insulin less often.
You just can't shed those last 10 pounds.
When your weight loss efforts have plateaued, IF may serve to kick-start your metabolism, says Jubilee. “Your body learns that if there's no glucose available for fuel there are fat stores to burn for fuel instead,” she says.
Over 40 and struggling to lose weight? You must do these 6 things:
Who shouldn't try intermittent fasting?
Steer clear if...
You take medication that impacts your blood sugar.
People who use insulin or drugs like metformin need to eat regularly, warns Foroutan. "If you go too long between meals you risk having your blood sugar fall way too low, which could be incredibly dangerous.”
You're a carb junkie.
You can theoretically eat whatever you want when you're on an IF plan (and not in the fasting phase), but if you overdo the carbs you'll have trouble keeping your blood sugar stable. Refined carbs, in particular, make your blood sugar rise and your insulin spike... and then you have a crash. So if you're trying to go without food for longer periods and your diet is too carb-heavy, you're going to end up pretty hungry and irritable.
You have an eating disorder or have had one in the past.
Anyone with anorexia or bulimia should absolutely steer clear. "People with a history of eating disorders involving restriction or binging and purging should avoid this way of eating,” says Jubilee. “Psychologically, it could mimic a restrict and binge phase" and become a trigger for your disorder to flare up. (Anorexia and bulimia aren't the only eating disorders. Here are 5 that you may not have heard of.)
You're pregnant or planning to become pregnant soon.
Hopefully this one is a no-brainer, but pregnancy is not usually the time to focus on shedding fat, says Jubilee. Unless your doctor has instructed you otherwise, focus on getting good nutrition throughout the day, every day.
You're on meds that need to be taken with food in the morning and before bed.
This isn't always a deal breaker, says Jubilee, since you might be able to take a few tablespoons of butter or coconut oil with your meds to ease their absorption without upsetting your stomach or your fasting schedule. But talk to your doctor, since IF may still not be the best choice for you.