In the good old days of the Melbourne Fashion Week, the wraith-like models used to flit back and forth from the make-up chair to rear entrance and make of themselves a fire hazard with cigarettes.

Smoking was one of their desperate strategies to keep the weight off.

If a new study is correct in its findings, smoking does in fact lend its devotees a lower body weight.

But, get this, it invariably causes the accrual of more belly fat, particularly the wretched visceral fat that settles like lava throughout the organs. This is the stuff linked to a higher risk of heart disease, diabetes, stroke, and dementia.

But hang on, models are thin

Yes, but visceral fat is hard to see. According to a statement from the Society for the Study of Addiction, which published the new paper:

“You can have a flat stomach and still have unhealthy amounts of (visceral fat), raising your risk of serious illness.”

The new study offers “supportive evidence that smoking may cause that type of fat to increase”.

Scientists from the NNF Center for Basic Metabolic Research, University of Copenhagen, found that both starting smoking and lifetime smoking may increase abdominal fat, especially the deep-seated nasty kind.

How did they make this discovery?

The researchers used a form of statistical analysis called Mendelian randomization (MR) to determine whether smoking causes an increase in abdominal fat.

For this they combined the results of two large-scale underlying European ancestry studies. One of these looked at who had smoke and who had not. The other looked at body fat distribution (measured by waist-hip ratio and waist and hip circumferences).

According to the statement from Addiction:

The researchers used these genetic studies to identify which genes are linked to smoking habits and body fat distribution.

Next, they used this genetic information to determine whether people with genes associated with smoking tend to have different body fat distributions.

Finally, they accounted for other influences, such as alcohol consumption or socioeconomic background, to ensure that any connections they found between smoking and body fat distribution were truly due to smoking itself and not other factors.

What the researchers say

Lead author Dr. Germán D. Carrasquilla, an assistant professor at Copenhagen, explained:

“This study found that starting to smoke and smoking over a lifetime might cause an increase in belly fat, as seen by measurements of waist-to-hip ratio. In a further analysis, we also found that the type of fat that increases is more likely the visceral fat, rather than the fat just under the skin.”

He said that previous studies had been prone to “confounding, which happens when an independent variable affects the results”.

Because the study design used genetic variations, “it does a better job of reducing or controlling for those variables”.

He said the influence of smoking on belly fat seems to happen regardless of other factors such as socioeconomic status, alcohol use, ADHD, or how much of a risk-taker someone is.

The researchers determined that excess abdominal fat in smokers was predominantly visceral fat by studying how DNA variants linked to smoking habits and belly fat relate to fat compartments in different parts of the body.

The key finding is that these genetic factors are more strongly linked to increased visceral adipose tissue – the deep fat that wraps around the abdominal organs – than to subcutaneous fat that is stored under the skin.