Metabolic Characterization of Overweight and Obese Adults

Research Team Members: Katie R. Hirsch, Abbie E. Smith-Ryan, Malia N.M. Blue, Meredith G. Mock, Eric T. Trexler, Kristin S. Ondrak

Why did you do this study?

Metabolic syndrome is a chronic disease characterized by the presence of multiple risk factors, including insulin resistance and poor cholesterol, which are associated with an increased risk for the development of cardiovascular disease, type-2 diabetes, and other metabolic diseases. The presence of excess body fat is highly associated with the development of metabolic syndrome, however, previous studies have identified a significant portion of overweight and obese individuals who have no risk factors and are considered metabolically healthy despite having a high percentage of body fat.

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Body composition scan using dual-energy x-ray absorptiometry

Despite an apparently normal metabolic status, excess body fat and difficulty achieving a healthy body composition may indicate the presence of underlying metabolic dysfunction overlooked by standard clinical tools. Currently, body mass index (BMI), cholesterol, and blood lipid levels serve as the primary screening tools for health risk.  However, the diagnostic value of these measures is limited by the inability to evaluate body composition (the differentiation between fat mass and lean mass) and fat distribution.  Regional distribution of body fat describes where an individual tends to store body fat.  Greater fat in the abdominal region and around the organs, known as visceral fat, is highly associated with insulin resistance in both overweight and normal weight individuals.  Visceral fat is also more highly associated with metabolic dysfunction than total body fat.  Lean mass (which includes muscle and organs) also has important associations with metabolic health.  Low relative lean mass is associated with insulin resistance, decreased metabolic rate, impaired fat metabolism, and poor functionality in activities of daily living, all of which are associated with weight gain and metabolic dysfunction.  Finally, hormonal imbalances, specifically related to insulin, leptin, estradiol, and cortisol, can lead to an unfavorable distribution of fat in the abdominal region, impair fat and glucose metabolism, and may also negatively impact energy expenditure.

 

Although traditional metabolic risk factors are highly associated with health risk, a more comprehensive evaluation of metabolic health may be a more appropriate and sensitive approach to evaluating metabolic status, regardless of body weight.   Evaluation of non-traditional metabolic factors, such as visceral fat, lean mass, resting metabolic rate, substrate utilization, and hormonal status, could provide valuable insight into aspects of metabolic health that may otherwise be overlooked. This in turn could improve the detection, prevention, and treatment of metabolic health issues. Therefore, the purpose of this study was to characterize metabolic health in overweight and obese adults using traditional and non-traditional metabolic variables.

What did you do and what did you find in this study?

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Resting metabolic rate test using a ventilated canopy and indirect calorimetry.

Body composition, visceral fat, resting metabolic rate, resting substrate utilization (use of carbs or fat for energy at rest), fasting cholesterol, blood lipids, glucose, and the hormones insulin, leptin, estradiol, and cortisol were measured in forty-nine overweight and obese men and women.  When evaluating traditional metabolic risk factors (blood glucose, triglycerides, and HDL cholesterol) 86.7% of the individuals had no more than one risk factor and 92% had no more than two risk factors, meaning this group could be considered metabolically healthy by traditional standards.  When evaluating visceral fat, in addition to traditional risk factors, the proportion of individuals considered to have metabolic dysfunction increased to 28.9%.  The occurrence rate increased to 80% when all metabolic risk factors were considered, classifying a majority of the group as metabolically dysfunctional. For men, the most common risk factors were high LDL cholesterol (82.6%), low metabolic rate (60.9%), low HDL cholesterol (47.8%), and high total cholesterol (43.5%).  For women, low HDL cholesterol (50.0%) and high LDL cholesterol (50.0%) were the most common risk factors, followed by low metabolic rate (30.8%), high visceral fat (19.2%), and greater reliance on carbohydrates for energy at rest (19.2%).

How do these findings impact the public?

 

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Ultrasound image of visceral fat thickness. Measurement was taken from the abdominal muscles to the aorta.

Results of this study show the importance of evaluating metabolic health beyond traditional diagnostic criteria. Evaluating components of body composition and metabolic function, such as visceral fat, lean mass, resting metabolic rate, and substrate utilization, in addition to hormonal and metabolic profiles, can give significant insights into metabolic status regardless of body weight and BMI status.  Knowledge of these factors could significantly improve lifestyle treatment approaches. Further, men and women exhibited different frequencies of risk factors, likely attributable to differences in fat distribution and hormonal status, reinforcing the importance of sex-specific evaluations. A unique aspect of this study was the use of ultrasound to measure visceral fat. Portable equipment, such as ultrasound, can improve the accuracy and evaluation of abdominal obesity-related risk, which is currently not evaluated in a clinical setting.  Additionally, connecting individuals with metabolic specialists who have access to more extensive assessment tools could lead to more effective intervention approaches.

 

 

 

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