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Monday’s medical myth: smoking helps control your weight

Over time, smokers gain as much weight as the rest of the population. Flickr/Difei Li

One of the few positives put forward by smokers to justify their habit is that it helps keep their weight in check. And while smoking may be harmful to their health, so is obesity.

So how does this claim measure up?

The health harms of smoking are well known – it is one of the world’s leading causes of illness and death. But the rising rates of obesity have overtaken smoking as the leading independent risk factor contributing to poor health.

When you combine smoking and obesity you get a major health hazard which cuts the average life expectancy by 13 years compared with non-smokers of a healthy weight.

Putting aside the undisputed serious health risks of smoking, is there any credence to the claim by smokers that their habit helps keep their weight in check?

A critical review of the medical research on smoking and weight management found that in the short term, nicotine can increase the body’s ability to burn energy and has a small effect on reducing appetite.

But rather than look at conclusions made from cross-sectional studies, which only look at current smoking status and body weight at a single point in time, we need to look at what happens to a smoker’s weight over time.

In these long-term studies, you find that smokers don’t control their weight any better than non-smokers.

When you combine all this research together, the “thin smoker” image may arise because thin people are more likely to take up the habit in the first place.

Once they start smoking, they gain just as much weight, and sometime even more, as the rest of the non-smoking population.

Surprisingly, very heavy smokers gain more weight than light smokers. This may be because low levels of physical activity, poor diet and alcohol are key culprits of obesity, and these lifestyle factors are known to cluster around heavy smokers.

So for someone thinking of quitting, should they expect their weight to balloon as a consequence?

Past research on smoking cessation and weight has shown the risk of weight gain is small but real.

Long-term quitters gain, on average, between three and five kilograms in the ten years after they quit. The risk of gaining weight is highest in the two years immediately after quitting and seems to decline thereafter.

But this is no reason to continue smoking. The health risks of cancer and metabolic disease places smoking at the bottom of the list for ways to control weight. Small changes to diet and physical activity can easily offset the slight amount of weight gained over several years after quitting.

The often-promoted “benefit” of controlling weight by smoking is greatly exaggerated, and more myth than reality.

Even if this myth were true, it’s far better for your health to be an overweight non-smoker than it is to be a thin smoker.

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