When you think of someone who smokes, perhaps an Audrey Hepburn figure comes to mind: a slender, chic Parisian type. Well, a new study suggests that even slim smokers could be hiding an unhealthy type of fat deep within their abdomens.
There is a common belief that smoking suppresses your appetite – and many smokers worry about gaining weight if they quit. However, while a new study has found that they are likelier to have lower body weights, smokers also tend to have more harmful deep abdomen fat.
This is called ‘visceral fat’, and it’s the unhealthy fat deep in your abdomen that’s linked to higher risks of heart attacks, diabetes, and dementia. In fact, visceral fat is so hard to spot that you could have a flat stomach and still be full of it.
To establish the link between lifelong smoking and belly fat, researchers from the University of Copenhagen used a statistical analysis tool called Mendelian randomisation (MR). This looks for causal relationships between exposures and outcomes (in this case, smoking and belly fat) by grouping people according to their genetic code. (That’s the set of rules that determines how your DNA is constructed.)
They applied this tool to the results from different genetic studies on smoking exposure and body fat distribution. These were large European ancestry studies: a study on smoking involving 1.2 million people who had just started smoking and over 450,000 lifetime smokers, as well as a body fat distribution study that included over 600,000 people.
First, the scientists identified which genes were associated with different smoking habits and body fat distributions (such as waist-to-hip ratios). They then used this genetic information to work out whether people with these genes had different body fat distributions from other people.
They adjusted the results to account for other influences on body fat, such as alcohol consumption and socioeconomic background, to make sure the link between smoking and belly fat was as clear as possible. What they found, though, was that the impact of smoking on belly fat was the same regardless of all these other factors.
Lead author Dr Germán D. Carrasquilla, who published the findings in the journal Addiction, said: “From a public health point of view, these findings reinforce the importance of large-scale efforts to prevent and reduce smoking in the general population, as this may also help to reduce abdominal visceral fat and all the chronic diseases that are related to it.
“Reducing one major health risk in the population will, indirectly, reduce another major health risk.”
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