New research reveals that extreme obesity in US youth, although still rare, has more than tripled since 2008, placing older teens and minority children at higher risk for serious metabolic complications.
Study: Prevalence of Extremely Severe Obesity and Metabolic Dysfunction Among US Children and Adolescents. Image credit: FotoDuets/Shutterstock.com
A recent study in JAMA Network Open investigated trends in pediatric obesity in the US and examined the association between the degree of obesity and comorbidities. Researchers highlighted the urgent need to address the surge in severe pediatric obesity in the US and develop effective public health interventions and policies to prevent this population from increased risk of metabolic and cardiovascular complications.
Pediatric obesity and metabolic disorders
According to the World Health Organization, a significant increase in pediatric obesity rates has occurred since 1990. A 2022 survey has documented a prevalence of 160 million children with obesity. It has also recorded 37 million children younger than 5 years and over 390 million aged between 5 and 19 years who were overweight.
Childhood obesity has been associated with various metabolic disorders, such as type 2 diabetes, dyslipidemia, metabolic dysfunction–associated steatotic liver disease (MASLD), and metabolic syndrome. A previous study has also revealed that obese children have hypertension.
In the US, childhood obesity is defined as body mass index (BMI) at or above the 95th percentile. Severe pediatric obesity has been defined as classes 2 (BMI ≥120% to <140% of the 95th percentile) and 3 (BMI ≥140% to <160% of the 95th percentile). Although many studies have indicated the adverse effect of childhood obesity, not many studies have investigated whether the degree of obesity severity is associated with specific comorbidities in childhood.
About the study
The current study added two more obesity classes, specifically class 4 (BMI ≥160% to <180% of the 95th percentile) and class 5 (BMI ≥180% of the 95th percentile), which are classified as extreme severe obesity. Although these classes still represent a small proportion of children, their prevalence rose by 253% between 2008 and 2023, from 0.32% to 1.13%. The prevalence and associated comorbidities of extreme severe obesity were assessed.
A total of 25,847 participants of the National Health and Nutrition Examination Survey (NHANES) from 2008 to 2023 were assessed. NHANES is a nationally representative survey conducted every two years to determine the health and nutritional status of the US population. As part of the survey, participants underwent a physical examination, provided blood samples, completed questionnaires about their health behaviors, and provided demographic information.
To assess metabolic dysfunction, liver imaging was performed. MASLD was defined by the presence of hepatic steatosis and at least one cardiometabolic criterion linked with diabetes or prediabetes, waist circumference, overweight or obesity, arterial hypertension, and hypertriglyceridemia. The Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) was calculated using the standard method. A HOMA-IR of 3.16 or greater defined pediatric insulin resistance, while severe insulin resistance was determined based on fasting insulin level of 50 μIU/mL or greater.
Study findings
The study cohort consisted of 49% female and 51% male participants, with a median age of 10.0 years and a median BMI of 18.4. Approximately 30.0% of the participants were non-Hispanic White, followed by non-Hispanic Black (23.9%), Mexican American (20.3%), and other racial backgrounds (14.6%).
The prevalence of any obesity increased from 19.46% in 2008 to 22.52% in 2023. More specifically, frequency of obesity classes 4 and 5 increased from 0.32% in 2008 to 1.13% in 2023. While the relative increase is striking, the study emphasized that these classes still comprise just over 1% of US youth. The prevalence of obesity increased consistently throughout the study period.
A positive linear correlation existed between the prevalence of classes 4 to 5 obesity for males and females. It must be noted that the incidence of extremely severe obesity increased steadily, particularly among adolescents aged between 16 and 18, by 1.99%, which was found to be significantly higher than 0.30% among children between 2 and 5 years of age and 0.39% among those aged between 6 and 8 years. Male sex, older age, and non-Hispanic Black and Mexican American ethnicity were each independently associated with higher odds of obesity in classes 4 and 5 (eg., odds ratio (OR) = 2.89 for non-Hispanic Black vs. all others).
Although no significant overall population-wide correlations between severe obesity and ethnicity were found, non-Hispanic Black children had the highest prevalence of classes 4 to 5 obesity in 2020-2023 compared to non-Hispanic White individuals and other racial categories. However, the multivariate analysis confirmed significant associations, showing that both non-Hispanic Black and Mexican American youth were disproportionately represented among extreme obesity cases, with differing metabolic profiles.
The study also noted that while non-Hispanic Black youth had a higher extreme obesity prevalence, they showed a lower prevalence of MASLD and metabolic syndrome compared with Mexican American peers, who exhibited higher rates of these metabolic conditions despite lower class 4 and 5 obesity prevalence.
The prevalence of MASLD was found to be highest among individuals with obesity classes 4 to 5 compared to those with obesity classes 1 to 3 and no obesity. MASLD affected 84.6% of children with obesity in classes 4 and 5 (OR = 6.74 for classes 4 and 5 vs. 1 to 3). Similarly, prevalence of severe steatosis, fibrosis, and prediabetes or type 2 diabetes increased with higher obesity class. The prevalence of liver stiffness was found to be significantly higher in individuals with obesity classes 4 to 5 than those with classes 1 to 3 and no obesity.
Notably, participants with extremely severe obesity also have higher alanine aminotransferase and γ-glutamyltransferase levels, compared to those with milder forms of obesity and no obesity. Similarly, the HOMA-IR was more elevated in participants with classes 4 to 5 obesity than in those with classes 1 to 3 or no obesity. Every child in the class 4 and 5 classes met the HOMA-IR threshold for insulin resistance, and 40.6% had severe insulin resistance (OR = 8.05 vs. classes 1 to 3).
The prevalence of pediatric metabolic syndrome was estimated to be 4.44%, 36.91% and 53.75% for participants without, classes 1 to 3, and classes 4 to 5 obesity, respectively. Triglyceride levels were not significantly different among participants with extremely severe obesity and those with milder forms of obesity. However, systemic inflammation was more prevalent in those with higher obesity classes than those with milder obesity.
The authors noted limitations, including the reliance on non-invasive liver imaging rather than biopsies, less-established pediatric cutoffs for FibroScan, and the relatively small absolute number of class 4 and 5 participants, which warrants cautious interpretation and replication.
Conclusions
The current study observed an increase in the prevalence of extremely severe obesity among US children and adolescents over time, particularly among older adolescents and non-Hispanic Black participants. An association between extremely severe obesity and incidence of severe metabolic and cardiovascular complications was observed.
Considering the increasing prevalence of pediatric obesity, an immediate public health intervention is required to alleviate the long-term burden of obesity-related diseases. The authors suggested prioritizing high-risk youth for scarce treatments such as GLP-1 agonists, alongside preventive strategies and policies to address racial and socioeconomic disparities and equitable access to emerging anti-obesity medications.
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