After spending the last few pages explaining that there is no such thing as a metabolic super-weapon, I now come to the topic of smoking. It’s a widely ac- cepted fact that quitting the habit leads to weight gain, and there are plenty of smokers who are afraid of quitting because it might make them fat.
The central question many people ask in this context is whether the weight gain is due to a metabolic effect, or to the fact that people who stop smoking are more likely to eat in order to compensate for the lack of oral stimulation they used to get from cigarettes.
The answer seems to be both. Just like caffeine or cocaine, for example, nicotine is a stimulant, and energy expenditure rises sharply by about 3 per cent after smoking.
Several studies have shown that smoking’s effect on the metabolism is equivalent to around 0 to 220 kcal per day on average, depending, of course, on how much a person smokes and how much they weigh — the increase in energy expenditure ap- pears to be less for obese smokers (Hofstetter et al., 1986; Moffat & Owens, 1991). Interestingly, there seems to be a placebo component to this energy- expenditure-increasing effect. In a study (Perkins et al., 1989), increased energy expenditure in subjects who were given a placebo nose spray was still around half that of subjects who received the real nicotine nose spray. Researchers also believe that behavioural factors play a part in this.
This means that smokers who kick the habit should expect their energy expenditure to sink to a normal rate and fall by up to 200 kcal a day — the amount for which nicotine consumption has previously been responsible. Since nicotine also has an acute appetite-suppressing effect, new non-smokers are likely to feel more hungry. Stamford et al. (1986) found an increased daily caloric intake of 227 kcal among women who gave up smoking, leading to an average weight gain of around 8 kg within a year. Of course, this isn’t a valid argument in favour of smoking.
Firstly, the habit can be just as deadly as the increase in metabolic rate described in the previous chapter. And secondly, no non-smoker would dream of thinking, Ah, yes, I’m willing to pay quite a lot of money and accept a life expectancy thirteen years short- er, for the sake of up to 220 kcal a day. But even if someone were to find that tempting, there are also weight-related disadvantages to smoking. For example, smoking appears to increase the levels of cortisone and other hormones in the blood, and leads to a tendency for fat to be stored in the abdominal region.
This increases smokers’ risk of developing a particularly harmful type of fat deposit, and although their BMI may be lower, their weight-related risk of developing certain health conditions, e.g., diabetes, is higher (Chiolero et al., 2008). At the end of this book, I deal in more detail with the issue of people with a high body-fat ratio despite being of normal weight, but smoking seems to be a major factor in this phenomenon. Inter- estingly, despite the energy-increasing and stimulating effect of nicotine, smok- ers tend to be less active on average than non-smokers, and they tend to take less exercise. It remains unclear to what extent this is thanks to their general lack of interest in health issues or to their impaired physical capabilities as a re- sult of reduced lung function.
There are many advice books and medical guidelines that claim that it’s diffi- cult, and therefore unreasonable, to try to lose weight and give up smoking at the same time. In fact, there’s no scientific evidence for this.
Spring et al. (2009) analysed studies on this topic and came to the conclusion that com- bining quitting cigarettes with a simultaneous diet does not produce worse re- sults, and there may even be some evidence of the opposite. It seems some people find it easier to make dramatic changes to their lives all in one go and establish entirely new routines.
Another possible hypothesis is that skin regenerates better when it is not ad- versely affected by smoking. Post-operation wounds are known to heal better in non-smokers, and there is ample scientific proof that smoking accelerates the ageing process of the skin.
So I can imagine that quitting smoking might very well have a positive effect on skin regeneration, which is another advantage when dealing with the temporary sagging skin during significant weight loss.
With regard to the fat logic in the title of this chapter, it only remains to point out again that giving up smoking does not automatically make you fat, just as pregnancy, illness, or ageing don’t, as long as the right balance is struck be- tween energy intake and expenditure.
It might seem trivial to point it out again, but quitting cigarettes does not make the metabolism slower, but rather returns