What Is Metabolically Healthy Obesity?
Obesity is a chronic metabolic illness defined as a body mass index (BMI) greater than 30 kg/m2.1 It is one of the leading causes of illnesses and deaths worldwide,2 associated with diabetes, cardiovascular disease (CVD; disease of the heart and blood vessels), liver disease, and certain types of cancers.3 However, recent studies show an interesting finding where a subgroup of those with obesity do not carry an increased risk of cardiometabolic diseases referred to as those with metabolically healthy obesity.4
How Is Metabolically Healthy Obesity Defined?
There is not yet a consensus on the definition of metabolically healthy obesity.5 However, all definitions agree that it describes an individual who is obese (BMI >30 kg/m2) but otherwise is metabolically healthy.6
Metabolically unhealthy obesity is often defined as those who are obese that meet one to four of the metabolic syndrome criteria: elevated triglycerides, reduced high-density lipoprotein cholesterol, elevated blood pressure, and elevated fasting glucose.6 Metabolically healthy obesity, on the other hand, can be defined as obesity without meeting any of the metabolic syndrome criteria. It is also commonly described as the absence of any cardiometabolic disorders, including type 2 diabetes mellitus, hypertension (ie, high blood pressure), dyslipidemia, and atherosclerotic cardiovascular disease (ASCVD; disease of the heart and blood vessels caused by the build-up of plaques) in obesity.5
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Metabolically Healthy Obesity5,6 |
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BMI |
>30 kg/m2 |
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Triglycerides |
<150 mg/dL |
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HDL Cholesterol |
>40 mg/dL in men >50 mg/dL in women |
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Systolic/Diastolic Blood Pressure |
<130/<85 mm Hg without antihypertensive treatment |
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Fasting Blood Glucose |
<100 mg/dL without glucose lowering treatment |
How Prevalent Is Metabolically Healthy Obesity?
Due to the varied definitions of metabolically healthy obesity, data on its prevalence is not entirely reliable.5 With large regional and sex-related variations, some studies estimate that the prevalence of metabolically healthy obesity is approximately 12%. Other studies show that the prevalence ranges from 2-28.5%. Following a strict definition of metabolically healthy obesity (obese without meeting any of the metabolic syndrome criteria), its prevalence is estimated to be around 12-17% in all adults with obesity.6
What Causes Metabolically Healthy Obesity?
Although research is still being conducted to understand what causes metabolically healthy obesity, there are unique characteristics to it that may help explain the underlying differences between metabolically healthy vs. unhealthy obesity. Studies have shown that individuals with metabolically healthy obesity have better cardiorespiratory fitness, greater insulin sensitivity, better insulin secretion, lower visceral fat mass, and lower inflammatory markers.5,7
A key characteristic in metabolically healthy obesity is the greater distribution of fat to peripheral adipose tissues, specifically in the lower body (ie, legs).5,7 One emerging hypothesis from this observation is that inadequate expansion of healthy adipose tissues lead to the storage of excess calories and fat in the upper body and organs that are not meant for fat storage. It is thought that this accumulation of visceral fat can lead to disruptions in organ function and eventually cause cardiometabolic dysfunctions. By allowing excess fat storage in peripheral tissues in the lower body, metabolically healthy obesity may avoid disruption of organ function and allow normal metabolic functions to continue. Additionally, individuals with metabolically healthy obesity are marked by the absence of insulin resistance as well as less inflammatory markers. Studies find greater insulin sensitivity, less infiltration of visceral fats by immune cells, favorable adipokine (ie, immune-related proteins released by adipose tissues) secretion pattern, and less inflammatory markers in individuals with metabolically healthy obesity.
How Does Metabolically Healthy Obesity Impact Health?
Metabolically healthy obese individuals do not (currently) carry cardiometabolic illnesses and have a more favorable long-term cardiovascular prognosis when compared to metabolically unhealthy obese individual.6 However, studies indicate that metabolically healthy obese individuals are at an increased risk of developing metabolic abnormalities in the future when compared to metabolically healthy nonobese individuals.5 For instance, some studies show that around half of individuals with metabolically healthy obesity develop at least one metabolic abnormalities in a 3-12 year follow-up period. Meta-analyses and large epidemiological studies also begin to show that metabolically healthy obesity is associated with increased risk of developing type 2 diabetes mellitus, ASCVD, cerebrovascular disease (eg, stroke), and heart failure when compared to metabolically healthy nonobese individuals.
Given that individuals with metabolically healthy obesity do not yet have cardiometabolic illnesses but are at increased risk, studies support the idea of prioritizing weight loss intervention and prevention of metabolic abnormalities in this population.5 Achieving and maintaining weight loss through healthy eating patterns, physical activity, and pharmaceutical or surgical intervention if necessary are important to prevent future cardiometabolic conditions in metabolically healthy obesity.
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References: |
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