Smoking has long been associated with weight management due to its appetite-suppressing effects. However, the detrimental health consequences of smoking far outweigh any perceived benefits, a recent research has suggested, highlighting that smoking, while potentially suppressing appetite, can lead to the accumulation of unhealthy abdominal fat, particularly visceral fat, which is linked to serious health risks such as heart disease, diabetes, stroke, and dementia.

Visceral fat is hard to see; you can have a flat stomach and still have unhealthy amounts of it, raising your risk of serious illness, said the researchers at the NNF Center for Basic Metabolic Research, University of Copenhagen as they used a form of statistical analysis called Mendelian randomization (MR) to determine whether smoking causes an increase in abdominal fat.

MR combines the results from different genetic studies to look for causal relationships between an exposure (in this case, smoking) and outcome (increased abdominal fat). This new study combined multiple genetic results from European ancestry studies of smoking exposures and measures of body fat distribution (e.g., waist-hip ratio and waist and hip circumferences).

The two underlying European ancestry studies were large in scale:  the smoking study looked at 1.2 million people who started smoking and over 450,000 lifetime smokers, and the body fat distribution study included over 600,000 people.

First, the researchers used previous genetic studies to identify which genes are linked to smoking habits and body fat distribution. Second, 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.

Lead author Dr. Germán D. Carrasquilla 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.”