Experts weigh in on intermittent fasting
The holiday season is in full swing and, even in these unusual times, it seems likely that the period between now and the new year will be filled with yummy, calorie-laden foods, such as cookies, pies and hot chocolate topped with whipped cream.
With so much temptation, some people might still be wondering how to control their weight. One popular weight loss method that’s emerged during the past few years is a technique called intermittent fasting, in which people severely limit their calorie intake in some way. Though loyalists claim to drop pounds this way, experts say just how effective the method is remains unclear.
“It’s a way people think they can lose weight very quickly,” says Kelly Gruber, a registered dietitian with Bridgeport Hospital. “But there’s not a lot of research out there.”
In fact, it’s hard to even accurately define intermittent fasting, because there are multiple techniques, experts say. Some intermittent fasters eat normally for five days of the week, then stringently restrict their calories (to anywhere from 400 to 600 calories a day, depending on the dieter) for two days of the week.
Other fasters have a window of time (usually about eight hours) in which to eat normally, then refrain from food for the remainder of the
day. Other methods can include an every-other-day method, in which fasters eat normally one day, then consume only a few calories the next.
“The studies are a little bit all over the place because there’s no standard definition of what intermittent fasting means,” says Ellen Liskov, outpatient nutrition specialist at Yale New Haven Hospital. “I’ve had clients tell me they’re interested in intermittent fasting, but that means different things to different people.”
She and other experts, Gruber included, say another complicating factor is that there isn’t a ton of research on intermittent fasting, and what’s there isn’t necessarily conclusive.
For instance, a study published in September in the Journal of the American Medical Assocation looked at 116 participants, some of whom were only allowed to eat between noon and 8 p.m., and some of whom observed a more typical meal plan, of three consistent meals with snacks throughout the day. The study showed that both groups lost weight and the researchers ultimately concluded that “time-restricted eating, in the absence of other interventions, is not more effective in weight loss than eating throughout the day.”
Other research, most of it in animals, shows evidence of weight loss, and some improvement in blood sugar levels, cholesterol levels and blood pressure. A paper published by Harvard Medical School in 2018 mentioned this, and added that research in humans has shown the method to be fairly safe and effective in humans, but perhaps not more so than other diet plans.
Many dietitians seem mixed on intermittent fasting. “It can be difficult, because it’s not something people are going to stay with long term and it doesn’t really teach you how to to eat correctly,” Gruber says. “It can lead to a calorie deficit over the course of a week, but, over the long-term, is it really a healthy eating pattern?”
There are potential drawbacks to intermittent fasting, says Sunida Infahsaeng, a registered dietitian, and director of clinical nutrition at St. Vincent’s Medical Center, in Bridgeport. If it’s not done under the care of a physician, it can lead to low blood sugar, low blood pressure, dehydration, headaches and other issues. Infahsaeng says another potential issue is that people can end up overeating on their “normal” eating days, resulting in no weight loss, or even weight gain.
And there are some groups of people who should stay away from intermittent fasting entirely, such as pregnant women, children, the elderly and those with diabetes.
But, for other groups there are possible benefits of this way of eating, Infahseng says. For one thing, it can make people more aware of what they consume during their eating windows, which could lead to healthier habits.
Dr. Joseph Feuerstein, director of integrative medicine at Stamford Hospital, says he sees one big benefit to restricting eating to one window of time during the day. “It stops you eating at night, which is a major weight gain factor,” he says.
Ultimately, experts say, if people are really interested in intermittent fasting, they should consult a medical professional first. “If someone tells me ‘I’m dead set on intermittent fasting — I’m doing this,’ then I will work with them to do it safely,” Gruber says.