When Krista Varady began studying intermittent fasting two decades ago, she felt her research wasn’t taken very seriously.
«All previous fad diets were either focused on calorie counting or low-fat diets,» he said.
but a new study de Varady and a team of researchers, published Monday in the Annals of Internal Medicine, showed that limiting food intake to a specific time period was as effective as calorie counting for weight loss.
Varady, a professor of nutrition at the University of Illinois, Chicago, and her colleagues enrolled 77 obese people in Chicago, the majority African-American or Hispanic, in their study, then assigned the participants to one of three routines for six months.
The first group practiced intermittent fasting, consuming all their calories between noon and 8 p.m. each day. The second group could eat whenever they wanted, but they recorded their calorie intake and reduced the total they normally ate in a day by 25%. The last group was the control group, so they did not change their usual eating habits.
After the six-month period ended, the researchers tested whether the changes helped people maintain weight. For six more months, the intermittent fasting group extended their eating window to 10 hours, and the calorie counting group ate enough calories to meet their energy needs.
The two groups that followed a diet in the first six months of the study generally maintained their weight loss after their diets ended, losing 5 percent of their body weight over the course of a year, Varady said.
By the end of the year, the intermittent fasting group had consumed 425 fewer calories per day, on average, than the control group and had lost about 10 more pounds. Meanwhile, the calorie-counting group ate about 405 fewer calories per day than the control group and lost about 12 more pounds.
«What we’re showing is that people don’t have to do these complicated calorie-counting diets, where people are always entering things into MyFitnessPal on their phone,» Varady said. «Instead of counting calories, they could only count time.»
Courtney Peterson, an associate professor of nutritional sciences at the University of Alabama at Birmingham who was not involved in the research, said Varady’s study is «the longest and best evidence we have of calorie counting versus intermittent fasting.»
Time-restricted eating, Peterson added, offers «a simpler rule that people can follow, and it’s producing the same weight-loss effect as counting calories, so that’s actually a big win, in my opinion.» .
Conflicting Research on Intermittent Fasting
Previous research on intermittent fasting has shown mixed results when it comes to weight loss.
a 2020 study found that restricting eating to a narrow period of time was no better for weight loss than eating throughout the day. Other studypublished in the Journal of the American Heart Association in January, suggested that eating fewer and smaller meals may actually be more effective for weight loss than time-restricted eating.
Yet others investigation has suggested that intermittent fasting could help people with obesity lose weight.
in a editorial Published alongside Varady’s research Monday, two Colorado researchers suggested that intermittent fasting likely only leads to weight loss under certain conditions.
Participants in Varady’s study, for example, had regular phone or Zoom calls with a registered dietitian.
«Support from a registered dietitian likely influenced people’s dietary choices within their 8-hour eating window,» the editorial said.
In general, people have more success with weight loss when they receive intensive counseling, said Dr. Adam Gilden, one of the editorial’s authors and an associate professor of medicine at the University of Colorado School of Medicine.
«Based on the results of the study, you wouldn’t just say to a patient, ‘Try time-restricted eating on your own without behavioral support,'» he said.
However, Varady said that most of the research has shown that intermittent fasting helps people eat less, which in turn helps them lose weight.
Peterson said that restricted eating windows can discourage mindless snacking or eating, and that longer periods of fasting can naturally reduce people’s appetites. But one of the main reasons intermittent fasting seems to help with weight loss, he added, is that people are willing to stick with it.
«Most people hate counting calories because they have to monitor everything they eat,» she said.
Nutrition experts also agreed that regardless of dietary strategy, people should consider the nutritional quality of their meals, such as the amount of fiber they eat or the amount of fruits and vegetables they eat. Studies have shown that highly processed foods, such as hot dogs, French fries, or soft drinks, can contribute to weight gain.
«There’s nothing magical about saying ‘I’m just going to eat for these eight hours a day,'» Gilden said. «The person doing that strategy still has to pay attention to the types of food he’s eating and the portions and amounts.»