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Intermittent fasting has become popular in recent years as an alternative to more traditional weight loss advice, including calorie counting, which can be cumbersome and difficult for some people to sustain.
The practice, also called time-restricted eating, can take many different forms, but typically people limit when they eat to a specific window of time, often six to eight hours.
A study released on Monday may have an answer.
« We really wanted to see if people can lose weight on this for a year? Can they maintain the weight loss? » He says Krista Varadaprofessor of nutrition at the University of Illinois, Chicago who has studied intermittent fasting for the past two decades and led the new study.
Varady’s research finds that intermittent fasting can actually help people lose weight and keep it off over the course of a year, with similar effects to calorie tracking. The clinical trial results were published In the Annals of Internal Medicine.
The amount of weight loss wasn’t dramatic — equivalent to about 5 percent of body weight — but the findings are encouraging for researchers in the field, in part, because they point out that people could stick with this habit over a long period of time. .
« This is pretty exciting, » she says Courtney Peterson, a nutrition professor at the University of Alabama at Birmingham who was not involved in the research. « This study has the most compelling results suggesting that people can go on it, which is not a fad diet, in the sense that people can do it for three months and fall off the wagon for a year. »
‘Natural Calorie Restriction’
Varady’s team recruited 90 adults with obesity (that is, a BMI over 30) from the Chicago area and randomly assigned them into three groups: one could only eat between noon and 8 p.m.; another had to count calories and reduce daily energy intake by 25 percent; and a third group made no changes to their eating habits.
After six months of weight loss, the participants had a « weight maintenance phase. » This was achieved by extending the eating window from eight hours to 10 hours in the intermittent fasting group and increasing calorie intake in the calorie restriction group.
Varady says he designed the study this way because « most people on a diet lose weight for about six months, after which it usually stabilizes. »
The study found that those who time-restricted eating lost, on average, about 10 pounds more than the control group, while those who counted calories lost about 12 pounds more. The difference between the two groups was not statistically significant.
« The key point is that you can basically get the same amount of energy restriction by counting time instead of counting calories, » says Varady.
Previous research on intermittent fasting found that when people limit their intake to an eight-hour window and deliberately limit calories, they achieve similar weight loss over the course of a year as people who only limit calories, but don’t limit intake at a specific time window.
What’s different in the new study is that people in the intermittent fasting group weren’t instructed to control their calories, but they still reduced their daily intake, by about 400 calories, the same amount as in the calorie-counting group.
The findings suggest that time-restricted eating can lead to a kind of « natural calorie restriction, » says Varady. He says it could be largely a result of people having less time to eat, particularly in the after-dinner hours.
« People usually eat in a 12-14 hour window, so all we’re doing is cutting about six hours, » she says, « We’re mostly cutting out, I think, after-dinner snacking. »
Peterson says that setting limits on when you eat can have a powerful « anti-snack effect » that can prevent mindless eating later in the night. He says his lab data also suggests that intermittent fasting can affect hormones and help regulate their appetite.
The study found no significant differences in cardiovascular and metabolic health between the two weight loss groups. Research suggests that eat first during the day it can be beneficial for metabolic health, but Varady says he chose noon to 8 p.m. because that mirrors how people tend to eat on a time-restricted basis in the real world.
« Feasibility-wise, I don’t know anyone who’s going to stop eating by 4 p.m. every day, » she says. « If you can do it or if it fits your lifestyle, then sure, go ahead. »
Support and advice can make weight loss more sustainable
Another feature of the study was that both weight-loss groups had regular consultations with dietitians in which they learned about « healthy food choices » and learned cognitive-behavioral strategies to prevent themselves from regaining weight.
This kind of « intensive support » is significant, he says Dr. Adam Gilden. « Most people who do it don’t do it with any kind of dietary or behavioral support. They’re doing it themselves, » says Gilden, an associate professor of medicine at the University of Colorado who authored an editorial that was published next to the new studio.
He says his patients often tell him they are unsuccessful when they try time-restricted eating.
Gilden indicates the results of another study that found that time-restricted eating didn’t lead to significant weight loss over the course of 12 weeks. In that study, she points out that there was no dietary advice and support.
In the study, where participants gained such support, « time-restricted feeding is about as effective as traditional calorie restriction, » she says. But he’s skeptical that these techniques will produce the same results in the real world without support.
In the study, those who consumed time-restricted eating and calorie counting had « moderately high adherence » throughout the year-long study.
But Peterson says previous research suggests the footwork involved in counting calories — what tends to be standard advice for people when they’re counseled on weight loss — makes it hard to back up. People need to be educated about portion sizes, how many calories are in different foods, and then track and record meals.
« It can be a big pain for a lot of people, » she says.
Peterson says this study’s comparison of time-restricted feeding to standard calorie counting suggests that « with much less effort, you can cut calories by the same amount. »
The implications of this research aren’t that intermittent fasting is somehow an « excuse to change your diet for the worse, » he says. Dorothy Searsprofessor of nutrition in Arizona State University’s College of Health Solutions and executive director of Clinical and Community Translational Science.
« We’re designed to optimally process nutrients throughout the day, » says Sears. « So we start by making people eat during the day and avoid eating at night, which in itself is associated with negative health outcomes. »
There’s no need to « arm wrestling » about whether calorie counting is better or worse, she says, « but we need to test whether time-restricted eating is as effective, and this study is showing, yes, it is effective. » .