Trends in the Prevalence of Metabolically Healthy Obesity Among US Adults, 1999-2018

Abstract

Importance: Improved understanding of trends in the proportion of individuals with metabolically healthy obesity (MHO) may facilitate stratification and management of obesity and inform policy efforts.

Objectives: To characterize trends in the prevalence of MHO among US adults with obesity, overall and by sociodemographic subgroups.

Design, setting, and participants: This survey study included 20 430 adult participants from 10 National Health and Nutrition Examination Survey (NHANES) cycles between 1999-2000 and 2017-2018. The NHANES is a series of cross-sectional and nationally representative surveys of the US population conducted continuously in 2-year cycles. Data were analyzed from November 2021 to August 2022.

Exposures: National Health and Nutrition Examination Survey cycles from 1999-2000 to 2017-2018.

Main outcomes and measures: Metabolically healthy obesity was defined as a body mass index of 30.0 (calculated as weight in kilograms divided by height in meters squared) without any metabolic disorders in blood pressure, fasting plasma glucose (FPG), high-density lipoprotein cholesterol (HDL-C), or triglycerides based on established cutoffs. Trends in the age-standardized prevalence of MHO were estimated using logistic regression analysis.

Results: This study included 20 430 participants. Their weighted mean (SE) age was 47.1 (0.2) years; 50.8% were women, and 68.8% self-reported their race and ethnicity as non-Hispanic White. The age-standardized prevalence (95% CI) of MHO increased from 3.2% (2.6%-3.8%) in the 1999-2002 cycles to 6.6% (5.3%-7.9%) in the 2015-2018 cycles (P < .001 for trend). There were 7386 adults with obesity. Their weighted mean (SE) age was 48.0 (0.3) years, and 53.5% were women. The age-standardized proportion (95% CI) of MHO among these 7386 adults increased from 10.6% (8.8%-12.5%) in the 1999-2002 cycles to 15.0% (12.4%-17.6%) in the 2015-2018 cycles (P = .02 for trend). Substantial increases in the proportion of MHO were observed for adults aged 60 years or older, men, non-Hispanic White individuals, and those with higher income, private insurance, or class I obesity. In addition, there were significant decreases in the age-standardized prevalence (95% CI) of elevated triglycerides (from 44.9% [40.9%-48.9%] to 29.0% [25.7%-32.4%]; P < .001 for trend) and reduced HDL-C (from 51.1% [47.6%-54.6%] to 39.6% [36.3%-43.0%]; P = .006 for trend). There was also a significant increase in elevated FPG (from 49.7% [95% CI, 46.3%-53.0%] to 58.0% [54.8%-61.3%]; P < .001 for trend) but no significant change in elevated blood pressure (from 57.3% [53.9%-60.7%] to 54.0% [50.9%-57.1%]; P = .28 for trend).

Conclusions and relevance: The findings of this cross-sectional study suggest that the age-standardized proportion of MHO increased among US adults from 1999 to 2018, but differences in trends existed across sociodemographic subgroups. Effective strategies are needed to improve metabolic health status and prevent obesity-related complications in adults with obesity.

Figure 1.. Trends in the Prevalence of Obesity, Metabolically Unhealthy Obesity (MUO), and Metabolically Healthy Obesity (MHO) Among US Adults, 1999-2018

A, Trends in the prevalence of obesity, MUO, and MHO among US adults. From 1999-2002 to 2015-2018, P < .001 for trend in obesity, MUO, and MHO prevalence. From 2003-2006 to 2015-2018, P < .001 for trend in obesity and MUO prevalence and P = .02 for trend in MHO prevalence. B, Trends in the proportion of MHO among US adults with obesity. From 1999-2002 to 2015-2018, P = .02 for trend. From 2003-2006 to 2015-2018, P = .51 for trend. Obesity was defined as a body mass index of 30.0 or greater (calculated as weight in kilograms divided by height in meters squared). Among participants with obesity, MUO was defined as having any component of the metabolic syndrome (waist circumference excluded) and MHO was defined as meeting none of the metabolic syndrome criteria. In A, prevalence estimates were age standardized to the 2000 US Census population, using 3 age groups (20-39, 40-59, and ≥60 years). In B, proportion estimates were age standardized to the nonpregnant adult population with obesity in the 2015-2018 National Health and Nutrition Examination Survey cycles, using the same 3 age groups. All estimates were weighted, and error bars indicate 95% CIs. Linear trends over time were evaluated using logistic regression. Specific estimates are shown in Table 2 and eTable 4 in Supplement 1.

Figure 2.. Trends in the Percentage of Individual Clinical Metabolic Parameters Among Adults With Obesity, 1999-2018

A, Elevated blood pressure (BP; systolic BP ≥130 mm Hg, diastolic BP ≥85 mm Hg, or hypertension medication use). No significant trend was observed from 1999-2002 to 2015-2018 (P = .28 for trend) or from 2003-2006 to 2015-2018 (P = .92 for trend). B, Elevated fasting plasma glucose (FPG; ≥100 mg/dL or antidiabetic medication use). A significant increasing trend was observed from 1999-2002 to 2015-2018 (P < .001 for trend) and from 2003-2006 to 2015-2018 (P = .02 for trend). C, Reduced high-density lipoprotein cholesterol (HDL-C; <40 mg/dL for men and <50 mg/dL for women). A significant decreasing trend was observed from 1999-2002 to 2015-2018 (P = .006 for trend) but not from 2003-2006 to 2015-2018 (P = .47 for trend). D, Elevated triglycerides (TG; ≥150 mg/dL). A significant decreasing trend was observed from 1999-2002 to 2015-2018 and from 2003-2006 to 2015-2018 (both P < .001 for trend). Percentage estimates were age standardized to the nonpregnant adult population with obesity in the 2015-2018 National Health and Nutrition Examination Survey cycles, using 3 age groups (20-39, 40-59, and ≥60 years). All estimates were weighted and the error bars indicate 95% CIs. Linear trends over time were evaluated using logistic regression.