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In 2012, British journalist Michael Mosley sparked a global trend with his BBC documentary ‘Eat, Fast and Live Longer’. Looking for an easy way to get healthy without growing his to-do list, Mosley discovered fasting. “What I discovered was really surprising: there are no pills, no injections and no hidden costs involved. It’s all a matter of what you eat. Or rather, what you don’t eat,” Mosley says in the introduction, accompanying a video of meat being seared on a Korean grill.
His 5:2 diet – two days of restricted eating (600 calories or less) and five days of no restriction – became widely popular.
In 2017, the 5:2 diet was still popular when Natalie Lister encountered obese adolescents in her Sydney clinic. Some of her patients at Westmead Clinical School Children’s Hospital were already trying intermittent fasting. Others asked her if they could. “But nothing had really been tested in young people,” she said.
Dieting is often counterproductive and leads to harmful weight fluctuations and the risk of eating disorders. And there’s no definitive evidence that intermittent fasting is helpful across the board, or leads to lasting health benefits. But given her patients’ independent forays into diet culture, Lister wanted to fill the knowledge gap and understand what benefits could come from a diet properly managed by health professionals.
To do this, Lister and her colleagues designed a pilot study and then a randomized clinical trial of intermittent fasting and other diets in teens with obesity-related health problems.
Results published in last month’s JAMA Pediatrics suggests that guided dieting, including intermittent fasting, could help some adolescents with weight-related health problems. They also found that well-managed diets can lower the risk of eating disorders and mental health problems. The findings could influence doctors’ decision-making as they face the challenge of balancing obesity treatment with the risk of causing eating disorders and other negative outcomes.
A new generation of anti-obesity drugs called GLP-1s provide obesity specialists with a powerful tool to help patients lose weight and potentially protect against a range of diseases. One in five American children is obese. Still, other doctors are reluctant to resort to injectable medications in children and adolescents, especially because patients may need to continue taking the medications for long periods of time to maintain weight. Furthermore, anti-obesity medications are not readily available to young people in Australia (including bariatric surgery). About 8% of children in Australia are obese. That’s part of why Lister and her collaborator, Hiba Jebeile, wanted to see how safe diets can be for children who are already at higher risk for eating disorders, depression and other health problems.
The data also comes as Washington takes a closer look at the country’s high rates of chronic diseases, especially among children, and what to do about it. At a hearing this week, lawmakers spent hours speculating about ways to use food to prevent and treat metabolic diseases such as obesity.
Starting with 800 calories per day
For the first month, 141 teenagers from children’s hospitals in Australia followed a ‘high-energy efficient’ diet of around 800 calories a day, using meal replacements such as sweet shakes and soups. Then half followed an intermittent fasting diet, with three restricted days (600-700 calories) and four unrestricted days. The other half followed a ‘continuously energy-restricted’ diet, with daily calorie limits between 1,400 and 1,700. This phase lasted almost a year.
Due to pandemic lockdowns, the research shifted to telehealth, which, along with frequent check-ins, meant participants received support from pediatricians, a dietitian and a psychologist. Adolescents with a diagnosed eating disorder were excluded, but some with disordered eating tendencies were eligible. Overall, about 20% of the children had symptoms of binge eating, and about half had symptoms of depression. The study also wanted to see whether adolescents with mental health problems and obesity would benefit from dieting.
Results and warnings
The primary goal of the study was to assess changes in BMI z-scores, a measure of how far above or below the average BMI they are for their age and gender. That’s standard practice for a weight loss clinical trial. But in practice, “this was not communicated to the young people at all,” Lister said. The adolescents set their own weight goals (which could not be lower than a calculated ‘healthy body weight’) and the discussions focused on their health and quality of life.
Weight loss mainly occurred during the first, most restrictive phase. Once divided into two groups, weight loss slowed but was largely maintained. In the intermittent fasting group, BMI z-scores decreased from a mean of 2.34 at baseline to 2.06 after 52 weeks (meaning the group’s mean BMI became slightly closer to the higher average for their ages and genders). The BMI in that group went from 34.83 to 33.21. In the group with continuous restriction, BMI z-scores decreased from a mean of 2.45 at baseline to 2.17 after one year. BMI went from 35.95 to 34.42.
Of the 141 participants, five in the intermittent fasting group and four in the continuous restriction group reached their target weight. No significant differences in weight loss were observed between the two diets.
Both groups saw small improvements in liver function, and the group with continuous energy restriction had reduced insulin resistance. There were no major changes in body composition or cardiometabolic health in either group. One participant developed gallstones and had to have their gallbladder removed, a side effect that the authors said “may have been related” to the diet.
The small improvements seen in the study could be helpful for children with obesity-related health problems, Lister said. But she also emphasized that these intensive interventions are intended for children with serious health problems – and not for general weight loss. More research is needed to understand which children would benefit most from a similar diet, both researchers said.
“It’s not about telling all children at school that they need to eat an energy-restricted diet every now and then because it’s good for their health,” says Lister. “We don’t want young people to do it alone, because that’s where the risks can be.”
Mental health benefits
Jebeile, who studies how weight loss affects mental health, has found that structured weight management programs often provide “overall benefit” to children’s mental health. This latest trial confirmed that finding. During the intervention, the teens showed less concern about their shape and weight and had fewer eating disorders, possibly due to consistent guidance and support from healthcare professionals. “Dietary restriction,” another warning sign of the risk of eating disorders, increased during the first four weeks of intensive dieting but normalized by the end of the trial.
Previous studies have found preliminary evidence that improvements in diet quality can improve mental health. In this study, many of the improvements in mental health came after the most restrictive period, which could indicate a general confidence boost from weight loss early in the study. But the participants also saw a dietician every week and could chat by telephone and text message. “We think it has to do with the support,” says Jebeile.
The researchers acknowledged that the pandemic lockdowns may also have affected participants’ symptoms. Reports of depression and eating disorders increased among Australian young people during the Covid lockdowns, according to several studies. The team plans further analyzes of nutritional data and long-term effects.
Seeking disordered eating
Despite the structured approach, some say that these diets – especially the restrictive phase of 800 calories per day – are very similar to the diets of people with eating disorders. “I see kids who we end up diagnosed with anorexia nervosa eating 800 calories a day,” says Christine Peat, a psychologist and clinical associate professor at UNC’s Center of Excellence for Eating Disorders.
Eating disorders are about more than the number of calories a person consumes, Peat acknowledged. But young people who are obese already are vulnerable to eating disorders.
In the Australian study, approximately 75% of participants had dieted before starting the weight management program. About a fifth of the participants showed an eating disorder. Because of these risks, all adolescents switched to a healthy eating plan in accordance with dietary guidelines at the end of the 52 weeks. The researchers also linked the children to primary care providers or dietitians, checking in six weeks after the end of the study period, and again after two years. That data will be published in a separate study.
Although the study showed a reduction in certain signs of eating disorders, the long-term risks remain uncertain. Research shows that eating disorders can take several years to emerge, but not many studies follow participants for that long (funding usually runs out).
Most participants reported at least one side effect, such as hunger, fatigue or irritability. Nearly a third quit, mainly due to the difficulty of the diet, although researchers said the course was normal for the type of intervention. One participant who withdrew was flagged as at risk for an eating disorder and subsequently diagnosed with anorexia. The researchers said this was proof that their screening and monitoring protocols are working. Jebeile said there were no differences in mental health between those who completed the study and those who did not.
The need for supervision
Lister and Jebeile emphasize that these diets are only safe under strict medical supervision and are not intended for widespread use among adolescents.
But consistent hand-holding from dietitians, paediatricians and obesity specialists is difficult to access in both the US and Australia. Clinical guidelines for childhood obesity, published last year by the American Academy of Pediatrics, were criticized for recommending a level of well-rounded care that does not exist in many communities.
That’s part of the reason why more research is needed, Jebeile said — to argue for more programs dedicated to that care. In future research, the team wants to tailor interventions to those who benefit most from them.
STAT’s coverage of chronic health conditions is supported by a grant from Bloomberg Philanthropies. Us financial supporters are not involved in decisions about our journalism.