Smoking keeps weight off: Study finds out how

By Dr. Ananya Mandal, MDJun 9 2011

A new study has finally shown exactly how smoking helps people keep off those extra pounds.

The researchers have found that nicotine activates a pathway in the brain that suppresses appetite. The study was published in the journal Science. The authors believe this discovery should lead to better diet drugs.

This comes after decades of research showing that smokers tend to be a bit thinner than non-smokers, and that smokers who quit tend to put on weight. Marina Picciotto, a professor of psychiatry at Yale and one of the study's authors said they stumbled upon this finding recently. The clue turned up during experiments looking for chemicals to treat depression, Picciotto says.

A scientist at Yale named Yann Mineur was giving mice a chemical that's a lot like nicotine, she said. “He was watching these mice and he said, ‘You know what, they don't eat as much as the mice that didn't get this medication.’ And so he decided to follow that up. It was a window into how nicotine might be decreasing appetite.”

There is previous evidence that nicotine must be triggering a response in certain brain cells. So they started looking at cells in the hypothalamus, a part of the brain known to regulate appetite. And they focused on a type of nerve cell, called POMC cells, known to be involved in eating behavior. They noted that nicotine made these POMC cells more active. But the researchers still needed to figure out how nicotine was communicating with these cells.

“On average smokers are 2.5 kilograms lighter than non-smokers,” said Picciotto. She said nicotine seems to lower their 'set weight', and once they give up the weight returns to normal. In their study the researchers gave nicotine to mice daily for 30 days and found that the mice reduced their food intake by nearly 50 per cent and lost 15 to 20 per cent of their body fat.

For this they looked at the receptors on the surface of the cells, Picciotto said. “And we actually thought that maybe the same nicotine receptors that make you want to smoke, that make you rewarded when you smoke, would be the ones that also control appetite. But we were wrong,” she said. So the team looked at another type of receptor – ones that are involved in fight-or-flight response. It turned out these fight-or-flight receptors responded to nicotine in a way that reduced hunger. That would make sense from an evolutionary perspective, Picciotto said.

“The fight-or-flight response is one where you actually want to preserve your energy to do something very important…So maybe you don't want to be out there eating while you're supposed to be running away from a tiger,” she explained.

The nicotine research does not mean people should take up smoking to lose weight, Picciotto warned. But for people who already smoke and want to quit, but don't want to put on weight, she says, nicotine gum or a patch might help. The damage done to the heart, lungs, fertility and even to the face far outweigh any benefits of losing a few pounds, she emphasized.

Michael Cowley, who directs the Obesity and Diabetes Institute at Monash University in Melbourne, Australia said if people used a nicotine patch, “you might find that patients do lose weight but then become dependent on a patch all the time.”

Fortunately, Cowley said, Picciotto's new research hints at a much better solution: drugs that suppress appetite without triggering the brain circuits involved in addiction. “What this shows is that there's a whole new class of drugs that can potentially be used as weight-loss agents.” Cowley said. Picciotto's lab has already shown that a nicotine-like chemical called cytisine causes mice to eat less. Cytisine comes from a natural source: the laburnum plant, a flowering shrub found in Eastern Europe, Picciotto explained. She says it's sold there as an herbal smoking cessation product.

Professor Andrew Lawrence of the Florey Neuroscience Institutes in Melbourne says Picciotto's team “have carried out a very elegant series of experiments”. He thinks the appetite suppressant effects may also help schizophrenia patients on antipsychotic drugs, which have a side-effect of putting on weight. “There is poor compliance, as these drugs cause marked weight gain…Something like this may help,” he said.