Why smoking keeps you skinny

Cosmos Online by Jasmine Malone

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LONDON: Nicotine suppresses the appetite by switching off the receptors associated with appetite and food intake, American researchers have found.

Their findings, published in the current issue ofScience show how smoking creates an anorexic effect in particular parts of the brain in mice. This could eventually help scientists develop nicotine-based therapies to aid both the ongoing battle against obesity and smoking addiction in humans.

"We have to be very cautious," said Yann Mineur from Yale School of Medicine, one of the study's authors, "but the basic biology, as far as we can tell, is fairly similar to what's happening in humans."

A way to lose weight

Smoking is one of the leading preventable causes of death in Western countries. It has been increasingly cited as a way to lose weight, a theory confirmed by the fact that smokers are on average thinner than non-smokers.

Conversely, a high proportion of people cite weight gain as a negative result of quitting smoking.

Although previous studies have attributed the effects of smoking on the appetite to nicotine, exactly how nicotine influences the brain in terms of food intake and consequential body weight has not been shown until now.

Smokers less hungry

Mineur and colleagues reported that they have determined the pathways affected by nicotine receptors on the central nervous system that result in loss of appetite and subsequent weight loss.

The researchers performed a combination of molecular, pharmacological, electrophysiological, behavioural and genetic knockdown experiments on mice to discover that nicotine influences a collection of central nervous system circuits, known as the body’s hypothalamic melanocortin system, by activating certain receptors.

These receptors, in turn, increase the activity of POMC neurons, known for their effects on obesity in humans and animals, along with a specific set of melanocortin 4 receptors.

It was found that the mice subjected to nicotine and nicotine-effect stimulants lost approximately 15-20% of their body mass over time and consumed almost half the portion of food, with water intake remaining unaffected.

Lose weight AND quit smoking?

The results shed light on the molecular and synaptic mechanisms that underlie the weight loss and decreased appetite that come with nicotine and could contribute to the development of both smoking cessation therapies and helping with obesity and metabolic disease, the researchers said.

But does this mean that the appetite-suppressant properties of nicotine could one day be exploited to combat obesity and help with smoking cessation, ultimately addressing two of the biggest health problems in one cure?

John McNeil, Head of Preventative Medicine at the Monash University School of Public Health and Preventive Medicine, who was not involved in the study, is hopeful, "Fear of weight gain after ceasing smoking is a common reason why people continue to use cigarettes," he said.

"The understanding of a mechanism for this may lead to ways to stop weight gain after smoking cessation and may also lead to new insights into weight control per se."