Scientists have known for decades that nicotine has the power to suppress appetite, but a team of researchers from the University of Pittsburgh wanted to take a closer look at the link. Their findings, published in the journal Nicotine & Tobacco Research, demonstrate how nicotine affects a person’s ability to gain and lose weight even while their calorie intake stays the same.

"The findings are important as they indicate that low nicotine levels may still reduce body weight, possibly motivating continued use and maintaining exposure to harmful chemicals in cigarette smoke,” said the study’s lead author Laura Rupprecht, a researcher at the University of Pittsburgh’s Center for Neuroscience, in a statement.

For the study, researchers conducted a series of four experiments to test how nicotine affected rats’ body weight. For the first step, researchers injected  nicotine into the rats and then measured their body weight over a 24-hour period to record any fluctuations. Then, they injected nicotine into another group of rats while they ate to see if it changed their appetite or influenced their weight. In a fourth experiment, they injected rats with various doses of nicotine while also cutting off some of their food supply. And finally, they gave a last group of rats free range to consume as much nicotine as they wanted from a saline serum over the course of 50 days, at the end of which their weight was recorded.

After looking at the results of each experiment, researchers discovered a pattern between nicotine exposure and weight. When the mice were cut off from the nicotine, they gained a substantial amount of weight despite the fact that their calorie intake remained the same.

Although there have been many studies connecting weight gain to quitting smoking, this is the first time researchers have found people can gain weight despite maintaining the same eating habits. Previously, it was thought that quitters replaced their smoking habit by eating more. This may not be the case, however, and the researchers said it could have something to do with the participants’ neurology.

In a 2011 study published in the journal Science, researchers found that nicotine hooks its users and suppresses their appetite. Many researchers have already pinpointed the pathway that it activates in the brain, and are now focusing on it in hopes of developing better diet drugs. But the detriments of smoking far outweigh nicotine’s ability to keep a user’s weight under control.

When a smoker inhales from the end of their cigarette, a plume of smoke enters their lungs and nicotine travels through the bloodstream into the brain. There, it links up with a receptor that has 15 subunits, each with its own job — increasing blood pressure, activating its addictive properties, cueing feelings of relaxation, and lowering appetite, for example.

According to the Centers for Disease Control and Prevention, cigarette smoking accounts for more than 480,000 deaths every year, making it the leading cause of preventable disease and death in the United States. Yet roughly 40 million adults in the country still smoke cigarettes while 16 million are currently living with a smoking-related disease today.

In another study, published in the journal PLOS One, researchers found that within three months after quitting smoking, most gained about 2.5 pounds. The study’s authors wrote: “Body weight gain itself is considered a factor that hinders the desire to quit smoking. From these considerations, for effective smoking-cessation treatment, one must determine the patients [who are] expected to gain weight after ceasing smoking, and perform weight control accordingly.”

Source: Rupprecht LE, Sved AF, Smith TT, and Donny EC. Self-Administered Nicotine Suppresses Body Weight Gain Independent of Food Intake in Male Rats. Nicotine & Tobacco Research . 2016.