While smoking is associated with some health problems, it is often overlooked that it also possesses some health benefits. In particular smoking is associated with a lower body weight, although the exact reasons for this are not clear. Originally it was believed that smoking was associated with weight loss because smokers consumed less energy than non-smokers, but studies indicate that this is not the case. In fact some evidence suggests that smokers eat more than non-smokers. Some studies have concluded that the weight loss effects of smoking are due to increased central nervous system activation brought about by nicotine (here). However, this is controversial because it is not clear how much nicotine is required for an effective weight loss effect. Whatever the mechanisms, evidence shows that weight gain is a likely result of smoking cessation. In fact, some of this weight gain effect from smoking cessation might result from the replacement of nicotine with sugary foods that are required by the reward pathways of the brain as replacements for nicotine.
The weight gain associated with cessation of smoking has been investigated in the nutritional literature. For example, in one study1, researchers recorded the metabolic and physiological changes in 13 sedentary female smokers following smoking cessation. Subjects who managed to maintain the cessation for over a year gained an average of 8.2 kg, supporting evidence that smoking cessation causes weight gain. This weight may have resulted from an increase in energy intake from 1765 to 1992 kcal per day. While it is tempting to claim that the calories caused the weight gain, subjects reported an increased consumption of sweets following cessation, suggesting that a shift in diet quality may have been the driver of weight gain. Despite this increase, macronutrient ratios remained similar between baseline and the cessation period, suggesting that sugar had replaced more complex carbohydrate. Interestingly, alcohol consumption also went down following cessation, which may account for some of the weight gain (here).
Assessment of the weight gain revealed that during an initial 48 day period, 96 % of the weight gain was from fat, whereas 4 % resulted from lean tissue and water. Of the subjects 10 did not maintain cessation and the 4.6 kg they gained initially was lost when they returned to smoking, such that after one year they had no net gain in weight. Assessment of the metabolic rates of the subjects via respiratory exchange ratios suggested that there were no changes to the resting metabolic rates (RMR) of the subjects through acute smoke inhalation or chronic cessation of smoking. These results contradict other studies in that the smoking did not alter the RMR of the subjects. During the initial 48 day cessation phase, the high density lipoprotein (HDL) of the subjects increased around 15% (7 mg/dL). However, the total cholesterol also showed a trend to increasing which prevented improvements in the HDL to total cholesterol ratio. Those subjects who did not maintain cessation had HDL levels return to their baseline measurements after 1 year.
So what can someone expect following cessation of smoking? Well it is likely, but not inevitable that, weight gain in the form of body fat will result. This may relate to increased intakes of sugary food that act as a surrogate for the removal of the addictive nicotine. Activity records showed that the subjects did not alter their physical activity patterns following cessation, so the effects of exercise cannot be determined from this study. The decrease in the consumption of alcohol may have contributed to weight gain because higher alcohol intakes are associated with lower body weights, but this relationship is not clear. Because nicotine is known to stimulate the central nervous system and raise RMR, the lack of an effect in this study are interesting. If nicotine is a causative factor in the inverse association between smoking and body weight then substituting coffee or tea for cigarettes may be beneficial. Methylxanthines can also raise RMR and so increased consumption may be able to offset reductions in RMR caused by nicotine withdrawal.
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