Can Intermittent Fasting Help Combat Youth Obesity?

Now, a small number of doctors and researchers are evaluating types of intermittent fasting in adolescents, searching for solutions as rates of obesity and Type 2 diabetes rise. One pediatric endocrinologist in Los Angeles is launching a clinical trial looking at eating within a set time window in adolescents with obesity. Researchers in Australia are completing a separate trial, the results of which they expect to publish later this year.

Roughly one-fifth of children in the U.S. are considered obese, according to data from the Centers for Disease Control and Prevention. Pediatricians are so concerned that the American Academy of Pediatrics for the first time this month recommended physicians offer weight-loss drugs for children with obesity. 

Any approach that limits when and how an adolescent eats must be handled cautiously, doctors say. 

Families and doctors need to be very careful with any form of intermittent fasting in youth as it can be a slippery slope with a potential risk of eating disorders, says

Jason Nagata,

a pediatrician and eating-disorder specialist at the University of California, San Francisco. Doctors have also raised questions about the potential long-term effects of intermittent fasting on developing bodies.

Courtney Peterson,

an associate professor of nutrition sciences at the University of Alabama at Birmingham who studies intermittent fasting in adults, says she would be worried about adolescents’ getting enough nutrients. “I think it’s worth testing but testing with caution,” she says. 

Her research has found that adults with obesity who ate between 7 a.m. and 3 p.m. lost on average an extra 5 pounds more than a control group eating over 12 hours or more, and adults with prediabetes who ate over a six-hour period starting early in the day showed improvements in blood-sugar levels.

Intermittent fasting is an umbrella term for eating strategies that involve fasting. One such strategy, time-restricted eating, or TRE, limits eating to a set number of hours a day—often eight—with no limitations on what or how much you eat. In the remaining hours, you refrain from eating or drinking except for water. 

Alaina Vidmar,

a pediatric endocrinologist and obesity-medicine specialist at Children’s Hospital Los Angeles, is starting a clinical trial to evaluate whether an eight-hour window of eating, from 11 a.m. to 7 p.m., results in changes in insulin and glucose response for teens with obesity. 

The researchers are also looking at weight loss and body-fat mass, as well as blood pressure and cholesterol. 

The research stems from conversations Dr. Vidmar had with families of patients with obesity in recent years. Some had asked her about time-restricted eating, or had tried it and said they liked it. She tested the concept in teenagers with obesity to see if setting an eight-hour window of eating was feasible in a pilot study published in the journal Nutrients in 2021.  

“They enjoyed doing it, they felt like their whole family could do it, and over time they were losing weight,” Dr. Vidmar says of the teens. 

Now, her lab is enrolling 100 youth between 12 and 21 years old with Type 2 diabetes and obesity in a 12-week trial. Participants are screened and monitored for any negative eating behaviors, she says. So far, she hasn’t found that time-limited eating “impacts eating behaviors or worsens disordered eating in any way,” she says. 

In Australia, researchers are studying how teens with obesity respond to a different form of fasting called intermittent energy restriction. 

In this approach, for three days a week you eat roughly one-quarter of the calories you normally do, says

Natalie Lister,

a researcher and dietitian at the University of Sydney. On the other four days, you have no calorie limits. 

Dr. Lister says she and colleagues started looking into intermittent fasting in adolescents with obesity a few years ago when patients started asking about it. They conducted a pilot trial with 30 adolescents, published in 2019. Now, the researchers are completing a trial whose results they expect to publish later this year. 

The health team monitors for eating disorders and depression, and the study doesn’t enroll anyone with a high risk of disordered eating, says Dr. Lister. Dietitians provide guidelines to help ensure participants are meeting nutritional requirements.

In adults with obesity, the data on TRE is mixed when it comes to weight loss, but two systematic reviews of the existing research both found a modest weight-loss benefit overall, says Dr. Peterson. Studies have also found that adults experience improvements in measures such as insulin resistance, reducing blood-glucose levels, particularly when their eating window starts early in the day. 

Matthew Muros, a 15-year-old in Carson, Calif., struggles with his weight and prediabetes. Matthew participated in Dr. Vidmar’s pilot studies last year. The first two weeks were challenging, he notes. 

“I did feel really hungry. I just kept on drinking water,” he says.

He says it got easier, and when the study was over he decided to stick with the schedule. He has lost about 30 pounds, and his blood-glucose levels have improved. 

He has also changed his diet, having less soda, fast food and carbohydrates. “I’m trying to eat a little bit more healthy,” he says.

Write to Sumathi Reddy at Sumathi.Reddy@wsj.com