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Belly Fat Risk for CVD Worse than We Thought

One type of belly fat may be more risky, according to results from an imaging-based study.

We know that subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) are associated with adverse cardiometabolic risk profiles.  For this study they explored the degree to which changes in abdominal fat quantity and quality are associated with changes in cardiovascular disease (CVD) risk factors.

Caroline Fox, MD, MPH, of the National Heart, Lung and Blood Institute in Framingham, Mass., and colleagues added that a review of abdominal computed tomography (CT) scans from participants in the Framingham Heart Study showed that fat accumulation deep in the abdominal cavity was more strongly associated with cardiovascular disease (CVD) risk than abdominal fat located under the skin.

The researchers wrote in the Journal of the American College of Cardiology that fat attenuation, or density, changes were also found to be associated with heart disease risk, with a shift toward lower density abdominal fat associated with an increased incidence of CVD.

They drew 1,106 study participants (44.1% women; mean baseline age 45.1 years) from the Framingham Heart Study Third Generation cohort who participated in the computed tomography (CT) substudy Exams 1 and 2.  Abdominal adipose tissue volume in cm3 and attenuation in Hounsfield units (HU) were determined by CT-acquired abdominal scans.

Researchers examined the impact of changes in subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) on CVD risk over a 6-year period. During the 6.1 years of follow-up, weight, body mass index (BMI), and waist circumference increased by an average of 2.4 kg, 1.1 kg/m2, and 3.7 cm, respectively. The results also showed that the mean fat volume was increased, and the mean fat attenuation change was decreased. An increase in fat volume and decrease in fat attenuation were associated with adverse changes in CVD risk factors. An additional increase in fat volume was associated with incident hypertension, hypertriglyceridemia, and metabolic syndrome. Similar trends were observed for each additional 5 HU decrease in abdominal adipose tissue attenuation. Most associations remained significant even after further accounting for body mass index change, waist circumference change, or respective abdominal adipose tissue volumes.

From the results it was concluded that increasing accumulation of fat quantity and decreasing fat attenuation are associated with worsening of CVD risk factors beyond the associations with generalized adiposity, central adiposity, or respective adipose tissue volumes.

The majority of these associations remained significant after controlling for BMI change, waist circumference change, or respective abdominal adipose tissue volumes, the authors reported.

Secondary analysis of participants with incident CVD risk factors across tertiles of fat volume and attenuation suggested that increase in change in fat volume, and decrease in the change in fat attenuation, were associated with relatively higher CVD risk factors.

The researchers wrote “Taken together, these findings suggest that adverse changes in fat quantity and attenuation are associated with changes in CVD risk factors above and beyond the contribution of generalized adiposity, central adiposity, or absolute levels of respective fat volume.”

They concluded that the findings, “highlight the importance of quantitative and qualitative aspects of adipose tissue for a better understanding of CVD risk.”

Ian J. Neeland, MD, and James de Lemos, MD, of UT Southwestern Medical Center in Dallas, wrote in an accompanying editorial that the study findings support a growing body of data showing that adipose tissue imaging can provide important information about cardiometabolic risk that BMI alone cannot.  But they added that questions remain, including how to assess fat function or dysfunction, while circumventing the invasive nature of tissue biopsy or cell culture assay. They continued to say that, “the ultimate question is whether it is possible to translate evaluation of ‘form’ (the anatomical measurement of adipose deposits) to assessment of ‘function,’ to unravel the pathophysiology of adipose tissue expansion, and circumvent the inherent limitations of BMI and isolated imaging-based fat quantification.”

The study’s observational nature was a limitation, as was the majority white patient population, so the results may not apply to other ethnic or racial groups.

Practice Pearls:

  • Carrying extra weight in the form of belly fat is a risk factor for cardiovascular disease, but one type of belly fat may be more risky than another.
  • Note that the study findings support a growing body of data showing that adipose tissue imaging can provide important information about cardiometabolic risk that BMI alone cannot.
  • Increasing accumulation of fat quantity and decreasing fat attenuation are associated with worsening of CVD risk factors.

Source:

Lee JJ, et al “Association of changes in abdominal fat quantity with incident cardiovascular disease risk factors” J Am Coll Cardio 2016; DOI: 10.1016/j.jacc.2016.06.067.