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Intermittent fasting worked as well as calorie restriction for weight loss in teens with obesity, and both methods could help with underlying mental health issues, analyses of an Australian randomized trial showed.

After 52 weeks, the of the study showed an estimated marginal mean change in body mass index (BMI) z-scores of -0.28 (95% CI -0.37 to -0.20) in the intermittent energy restriction (IER) group and -0.28 (95% CI -0.36 to -0.20) in the continuous energy restriction (CER) group. Significant reductions with both interventions were also observed for some cardiometabolic outcomes.

And a of the trial showed reductions in self-reported depression, eating disorder symptoms, and binge eating with both IER and CER. The findings were reported in JAMA Pediatrics by Natalie Lister, PhD, of the University of Sydney, and colleagues of the Fast Track to Health trial.

As the first randomized clinical trial to evaluate IER in adolescents, the researchers said the findings offer teens "more choice" and provide an option in addition to traditional calorie restriction for weight loss.

"Many adolescents were presenting to our hospital weight management clinics already following this diet or wanting to try this, yet there had not been any research to inform safety and effectiveness," Lister told MedPage Today. "In Australia, there are few treatment options for adolescents with obesity, which is associated with poorer immediate and long-term physical and mental health and well-being."

Body Composition, Cardiometabolic Outcomes

The trial included 141 teens with obesity (13-17 years; BMI of 30 or greater) and was divided into three phases: a very low-energy diet (weeks 0-4), intensive intervention (weeks 5-16), and continued intervention and/or maintenance (weeks 17-52). About two-thirds of the teens completed the trial, 43 in the IER group and 54 in the CER group.

For the first 4 weeks, all participants regardless of trial assignment adhered to an 800 kcal/day diet using micronutrient complete meal replacement products for three to four meals per day and low-energy food.

Starting at week 5, participants transitioned to either the IER or CER intervention. Those in the IER group ate approximately 600-700 kcal 3 days per week, alternated with 4 days per week of healthy eating based on the Australian Dietary Guidelines with no energy prescription. Those in the CER group had a daily energy prescription of 1,430-1,670 kcal/day for ages 13-14 years or 1,670-1,900 kcal/day for ages 15-17.

At week 17, there was no change unless participants reached their personal goal weight. Those who did were transitioned to a weight maintenance dietary plan.

Both IER and CER also reduced BMI overall (-1.62 and -1.53, respectively, at 52 weeks) and as expressed as a percentage of the 95th percentile (BMI95) by 9.56 and 9.23. By the end of the trial, 35% in the IER group and 27.8% in the CER group achieved a 5% reduction in BMI95.

Similarly, there also weren't significant differences between the two diets when it came to body composition including reductions in fat mass index (-1.59 for IER and -1.45 for CER) and fat-free mass index (0.13 for IER and -0.05 for CER).

Both groups had significant reduction in prevalence of insulin resistance -- defined as a fasting insulin-glucose ratio over 20 -- at week 16 (76.5% to 57.1% for IER; 86.8% to 51.7% for CER), but the difference only remained significant after a year in the CER group. By week 52, 61% of both groups met criteria for insulin resistance.

There were also no differences between the diets regarding change of percentage of teens with dyslipidemia and impaired hepatic function tests by week 52:

• Dyslipidemia: 43.7% to 23.9% for IER and 41.4% to 28.6% for CER
• Impaired hepatic function tests: 34.3% to 18.9% and 18.8% to 16%, respectively

"Doctors should be aware adolescents with high weight may present with cardiometabolic complications usually seen in adults," said Lister. "Dietary interventions can be effective at improving weight and cardiometabolic health, but young people need ongoing support from a dietitian to achieve this."

Psychiatric Outcomes

After a year, both diet methods yielded sustained improvements in self-reported depression (as measured by the Center for Epidemiologic Studies Depression Scale-Revised 10-Item Version for Adolescents scale) and eating disorder symptoms (on the Eating Disorder Examination Questionnaire), with no significant differences between the two groups:

• Depression (range 0 to 30): -2.70 for IER vs -3.87 for CER
• Eating disorder (range 0 to 6): -0.63 for IER vs -0.56 for CER

In addition, both dietary groups had reductions in binge eating. But long-term improvements in this domain (measured by the Binge Eating Scale; range 0 to 46) were only maintained in the IER group:

• Week 4: -4.38 for IER vs -3.44 for CER
• Week 52: -3.72 for IER vs -0.38 for CER

"Results suggest that obesity treatment interventions may have a dual role of improving physiological and psychosocial health," the researchers wrote, though they cautioned that a subgroup experienced an increase in depression and disordered eating symptoms. "Screening and monitoring for depression and disordered eating are important to facilitate early intervention."

Seventeen adolescents (12.1%) required support or referral for depression and/or disordered eating. Identified via dietetic monitoring, seven female teens (five in the IER group, two in CER) required additional support for disordered eating or body image concerns during the trial.

Two adolescents had mental health-related adverse events and were withdrawn from the study -- one due to the reemergence of prior body image concerns and one diagnosed with atypical anorexia nervosa associated with excess restriction and rapid weight loss.

All mental health outcomes were self-reported and therefore "should be interpreted with caution," the researchers said. For example, questions related to vomiting were sometimes misunderstood (vomiting due to migraines or gastroesophageal reflux were reported but were not self-induced vomiting).

"Further data on risks and long-term outcomes beyond 12 months of intervention are required to confirm clinical implications," the researchers noted.

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