One of the most common reasons that people try intermittent fasting is for weight loss, especially at the beginning of the year when health goals jump to the top of many to-do lists.
But a new study suggests that some people can achieve their weight loss goals without restricting their eating to certain times of the day.
Researchers say that calorie restriction appears more successful than intermittent fasting for weight loss.
Over the course of a six-year study, researchers found that people who ate a greater number of large or medium meals during the day were more likely to gain weight.
In contrast, those who ate smaller meals were more likely to lose weight during this time.
However, the time interval between the first meal and last meal of the day had no impact on people’s weight.
Researchers write that this suggests that the size and frequency of meals — along with total calories eaten per day — have a bigger impact on weight change than the timing of meals.
In the study, published Jan. 18 in the Journal of the American Heart Association, researchers enrolled nearly 550 adults from three health centers.
They obtained people’s height and weight measurements from electronic health records. This was used to calculate participants’ body mass index (BMI), which is a screening tool for overweight and obesity. A higher BMI does not always indicate higher body fat.
Participants used a mobile app for six months to record when they slept and the times and approximate sizes of their meals.
In addition, people completed surveys about their physical activity level, food intake, whether they were trying to lose weight, smoking status, and other factors.
Researchers followed participants for an average of 6.3 years, which included both the six months after enrollment and several years before.
The results showed that both large meals (estimated at more than 1,000 calories) and medium meals (estimated at 500-1,000 calories) were associated with increasing weight over the six-year follow-up.
In contrast, small meals (estimated at less than 500 calories) were associated with decreasing weight.
However, meal timing was not linked to weight change during the follow-up period. This included the time from the first to the last meal of the day.
A type of intermittent fasting called time-restricted eating involves limiting meals to a shortened period of time during the day, such as between 8 a.m. and 4 p.m.
The average meal window during the new study was 11.5 hours, with an average 12.5-hour fast.
There are other types of fasting, such as not eating on one day a week, or skipping the middle meal each day. The researchers did not look at these other kinds of fasting patterns.
Dr. Mir Ali, a bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, Calif., said the results of the study fit with what doctors see in the clinic.
“People who gain weight tend to eat larger meals, so they are getting in more calories throughout the day,” he said.
“It’s easier to get excess calories if you’re eating larger meals,” he said, “as opposed to more frequent smaller meals, which may help you keep the total calories down.”
Dr. William Dietz, a pediatrician and director of the STOP Obesity Alliance at The George Washington University in Washington, D.C., also pointed out that people in the study who ate a lot of small meals lost weight over the study period.
“This suggests that multiple small meals may have a modifying impact on satiety [feeling full],” he said.
However, many factors affect weight loss and gain, he said.
The study also found that people who ate more meals during the day tended to gain weight, which suggests that eating fewer meals might help them lose weight.
Molly Rapozo, a registered dietician nutritionist and senior nutrition and health educator at Pacific Neuroscience Institute in Santa Monica, Calif., cautioned against taking this too far.
People still need to make sure they are getting the right amount of nutrition, such as protein, fiber, healthy fats, vitamins and minerals, she said.
“I find that people who eat two or fewer times a day have a very hard time meeting their nutritional needs,” she said, “so I really push them to eat three times a day.”
“But it doesn’t have to be a full meal,” she added. “It can be a snack … a balanced snack.”
Although the study found that meal frequency and total calorie intake — as indicated by meal size — were linked to weight change, this was an observational study, so researchers could not prove direct cause and effect.
Another limitation of the study is that participants were asked to estimate the size of their meal, which Dietz said would be challenging for many people.
“I would have difficulty with that, too,” he said, “and [obesity research] is my field.”
One thing that this study showed, said Dietz, is how difficult it is to do good studies about meal timing and size, especially long-term studies.
Part of the challenge, he said, is different approaches work for different people.
“Some people benefit from intermittent fasting, such as consuming their meals in a 6- to 8-hour window,” he said.
Two earlier studies found that eating within an 11-hour or 8-hour window was associated with weight loss. Both of these were small, pilot studies.
In contrast, a larger randomized controlled trial found that fasting for 16 hours each day wasn’t more effective for weight loss than eating throughout the day.
Rapozo said she’s had clients who have had success by shortening their eating window to 11 to 12 hours. This can be done by stopping eating a few hours before bedtime.
However, “the people who end up losing weight [with time-restricted eating] are often the ones that end up eating fewer calories as a result of their eating time being limited,” she said.
One approach that Ali thinks may work for some people is to use a portion guide, of which there are many different versions, including a printable plate template.
“This helps people be more conscious of what they’re eating,” he said. “Sometimes they may not realize that they’re eating such a large meal or that the meal has so many calories.”
Whatever approach people take to meet their weight loss goals, Allison Chase, PhD, a clinical psychologist and eating disorder specialist with Eating Recovery Center, cautions against doing too much.
“Extreme [eating] measures can result in disordered eating patterns,” she said, “especially for those with predisposing biological or temperamental factors, such as genetics, increased anxiety or depression.”
She recommends that people seek out professional support to help them meet their health goals, taking into account their specific circumstances, including their physical and mental health.
“Using healthy and positive coping strategies — such as mindfulness, or healthy activities like social interaction or mindful movement — can be a way for people to follow through with their health goals, and not need to use unhealthy eating strategies to manage them,” she said.
Our experts continually monitor the health and wellness space, and we update our articles when new information becomes available.
Current Version
Jan 18, 2023
Written By
Shawn Radcliffe
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Gillian Mohney
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