The data came from a total of 5,627 females and 5,836 males, all aged over 20 years.
Based on the data, the researchers split the study participants into four groups:
low muscle mass and low body fat
low muscle mass and high body fat
high muscle mass and low body fat
high muscle mass and high body fat
In both sexes, the raw data showed that higher levels of fat were associated with higher CVD mortality, regardless of muscle mass.
However, after accounting for other factors that are known to affect CVD mortality, the relationship between body fat and the risk of dying from CVD changed completely in females.
After making these adjustments, the researchers found that females with high body fat and high muscle mass had a 42% lower risk of dying from CVD compared with females who had a low muscle mass and low body fat.
By contrast, males with high muscle mass and high body fat had a 26% reduced risk of dying from CVD compared with males with low measurements, while those with high muscle mass and low body fat had a 60% decreased risk.
The researchers believe that their study supports the need for a shift in the focus of the advice that healthcare professionals give to females. This shift is toward increasing muscle mass through physical exercise and away from weight loss.
“[I]t demonstrates the potential importance of advice to maximize muscle mass in women. This diverges from the current emphasis on weight loss in CVD prevention, and thus methods to practically achieve such body composition alteration need to be further evaluated.”
It is worth emphasizing that the apparent protective effect of fat in females only emerged after adjusting for other CVD risk factors.
Among these CVD risk factors were:
high blood pressure (hypertension)
diabetes and prediabetes
hormone replacement therapy (HRT)
There is a highly complex interplay between body fat and these other risk factors. For example, excess body weight increases the risk of diabetes and hypertension, which, in turn, raise the risk of CVD.
Nonetheless, the authors note several plausible ways in which fat might provide some protection to females.
For instance, they highlight research suggesting that fat in the thighs and buttocks has a protective effect on metabolism that offsets the harm from abdominal fat.
They also note that in premenopausal females, the body stores about 50% of its fat just beneath the skin in the thighs and buttocks, whereas in males, the body stores 98% of the total fat more deeply in the upper body.
During and after menopause in females, however, fat tissue begins to accumulate in the abdomen, where it is associated with increased CVD risk.
The authors also note that in individuals of the same age and weight, the female body tends to accumulate fat by multiplying the number of fat cells, whereas the male body typically grows larger fat cells.
Large (“hypertrophied”) fat cells are associated with negative metabolic consequences, they write.
The researchers acknowledge some limitations of their study.
Firstly, the study design did not allow them to prove cause-and-effect relationships between muscle mass or fat mass and CVD mortality, only associations.
In addition, they say that the technique that they used to measure the body composition of volunteers — called “dual energy X‐ray absorptiometry” or DXA — can overestimate muscle mass in older people and individuals who lead sedentary lives.