Smoking Doesn’t Make You Skinny — It Actually Increases Belly Fat

COPENHAGEN, Denmark — There’s no shortage of reasons to quit smoking, but just in case you need one more, researchers from the University of Copenhagen report that smoking actually promotes the development of more abdominal fat. While some believe cigarettes help people stay skinny, study authors say this age-old myth appears to be just that – a myth.

More specifically, a team from the NNF Center for Basic Metabolic Research states that both starting smoking and lifetime smoking may increase abdominal fat, particularly visceral fat. This unhealthy fat is found deep inside the abdomen and is linked to a higher risk of numerous serious health issues, including heart disease, diabetes, stroke, and dementia.

While it is true that smokers tend to have lower body weights than non-smokers, researchers say they also have more abdominal fat (and abdominal visceral fat). Visceral fat is hard to spot; you can have a totally flat stomach and still harbor unhealthy amounts of visceral fat, which means a higher risk of serious illness. This new research highlights supportive evidence that smoking may cause this type of fat to increase.

To conduct this study, researchers utilized a type of statistical analysis called Mendelian randomization (MR) in order to determine if smoking does lead to an increase in abdominal fat. MR works by combining the results from various genetic studies to search for any causal relationships between an exposure (in this case, smoking) and an outcome (increased abdominal fat). Study authors combined multiple genetic results from European ancestry studies focusing on smoking exposure and body fat distribution levels (waist-hip ratio and waist and hip circumferences).

Then, they used previous genetic studies to help ID which specific genes show a link to both smoking habits and body fat distribution. Next, genetic info helped determine if people with genes associated with smoking usually have different body fat distributions. Finally, researchers accounted for additional potential influencers like alcohol consumption or socioeconomic background in an effort to ensure all connections found linking smoking and body fat distribution were really attributable to smoking and not some other factor.

“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,” says lead author Dr. Germán D. Carrasquilla in a media release.

“Previous studies have been prone to confounding, which happens when an independent variable affects the results. Because our study design uses genetic variations, it does a better job of reducing or controlling for those variables. 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.”

“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.”

Study authors uncovered that the excess abdominal fat present in smokers was predominantly visceral fat using an analysis of how DNA variants linked to smoking habits and belly fat relate to fat compartments in different parts of the body. Their main conclusion is that these genetic factors are more robustly linked to increased visceral adipose tissue (the deep fat that wraps around the abdominal organs) in comparison to subcutaneous fat found under the skin.

The two underlying European ancestry studies used for this project were large in scale; the smoking study encompassed 1.2 million people who started smoking as well as over 450,000 lifetime smokers. The body fat distribution study included over 600,000 people.

The study is published in the journal Addiction.