Where, Not How Much Body Fat May Influence Health Risk

Where fat is stored in the body may play a bigger role in heart attack, stroke, and diabetes risk than the amount of fat overall, according to two studies presented at RSNA.  

In the first study, researchers from the United States studied 200 women and men to determine if there were sex-differences in body composition and ectopic fat depots and whether these may be associated with a sex-specific cardiometabolic risk profile.

Ninety-one men and 109 women (mean age 37) participated in the trial. All were non-diabetic and overweight or obese (mean BMI: 35.2±5.8 kg/m²) but were otherwise healthy. After an overnight fast, the subjects underwent DXA and CT for body composition, 1H-MRS at 3T of soleus muscle for intramyocellular (IMCL), and right hepatic lobe for intrahepatic lipids (IHL) quantification, serum glucose, insulin and lipids. Men and women were compared by ANOVA. Linear regression analyses between body composition measures and cardiometabolic risk markers were performed.

“We hypothesized that there are gender-based differences in body composition and ectopic fat depots and that these could be associated with gender-specific risk profiles for diseases like diabetes, heart disease and stroke,” lead author Miriam A. Bredella, MD, a radiologist at Massachusetts General Hospital and associate professor of radiology at Harvard Medical School in Boston, said in a release.

The results showed while the women and men were of similar age and BMI, the women had higher %fat mass by DXA and lower lean mass compared with the men. However, the men had more visceral adipose tissue (VAT) and VAT/abdominal subcutaneous adipose tissue (SAT), resulting in the “beer belly.” They also had more muscle mass, IMCL, and IHL, while the women had more femoral SAT. Compared to the women, the men had higher measures of cardiometabolic risk, including serum triglycerides, apolipoprotein B, fasting insulin and HOMA-IR. However, in women, VAT, IMCL, and IHL were strongly associated with these measures of cardiometabolic risk while in men these associations were weaker or non-significant.

In the second study, researchers recruited 188 subjects to determine if relative sarcopenia was associated with cardiometabolic risk markers in young adults with obesity.

One-hundred women and 88 men (mean age 36.8) participated in the study. They had a mean BMI of 35.0±5.7 kg/m². All subjects underwent DXA and CT for body composition, an oral glucose tolerance test (OGTT), fasting serum insulin, lipids, and inflammatory markers. DXA appendicular lean mass (ALM)/BMI was used as a measure of relative sarcopenia and subjects were divided by the ALM/BMI median. Groups were compared by ANOVA.

The results showed that although they were of similar age and weight, women with lower ALM/BMI (relative sarcopenia) had a higher mean 120-minute glucose level and higher glucose area under the curve on OGTT, lower HDL cholesterol, higher apolipoproteinB (ApoB) and ApoB/LDL, higher hsCRP and fibrinogen and lower muscle attenuation, suggestive of fatty infiltration compared to women with higher ALM/BMI. Again, despite being of similar age and weight, men with lower ALM/BMI had higher mean insulin, HOMA-IR, hsCRP, and fibrinogen, and lower muscle attenuation compared to men with higher ALM/BMI.

 “Sarcopenic obesity may be an under-appreciated mechanism linking obesity to cardiometabolic disease,” Bredella explained. “That stresses the importance of building up muscle mass in the setting of obesity.”