Both smoking and obesity increase the risk of mortality. However, smoking is inversely related to body weight. This suggests that something about the act of smoking, or its associated behaviour may prevent weight gain. While smoking is bad for the health and increases the risk of disease, it is interesting from a physiological perspective to consider the metabolic and behavioural changes caused by smoking cigarettes. Epidemiological studies investigating the association between smoking and body weight have generally concluded that smokers from all socioeconomic groups, both sexes, and of all ages, weigh less than their non-smoking counterparts. Upon cessation of smoking, around 10 lbs of weight is gained, and this might suggest that smokers are at least 10 lbs lighter than non-smokers, and that it is the act of cigarette smoking that is responsible for this effect. Smoking therefore may allow individuals to maintain a weight significantly lower than would be achievable without smoking.
Gaining body weight is far more complex than the oversimplified energy balance theory of weight gain. Multiple compartments within the body can be used to waste energy including the resting metabolic rate, the thermic effect of food, the thermic effect of exercise, exercise efficiency and adaptive thermogenesis. Smoking could affect any of these compartments from a metabolic perspective and therefore have a significant effect on body weight. The most obvious choice for a possible candidate as to how cigarettes affect body weight is nicotine. Nicotine is known to be able to cause a significant increase in the energy expenditure of animals through its stimulatory effect on the central nervous system. In addition, nicotine may alter gut physiology and this may decrease the absorption of nutrients, thus decreasing energy intake. Only 5 % of the smoked nicotine makes it to the gut in saliva, but nicotine absorbed to the blood from the lungs may act indirectly to decrease gastric motility and decrease gastric acid secretion.
In addition, nicotine can stimulate the cholinergic system of the brain and this can in turn modulate consummatory behaviour for drinking. This may explain the association between cigarette smoking and alcohol consumption. As drinking is inversely associated with body weight this may go some way to explain the inverse association between body weight and cigarette smoking. Drinkers have been shown to ingest more total calories, but less calories from sugar. This reduction in the amount of sugar consumed in the diet may therefore explain the inverse association between smoking and body weight. In addition, the consummatory behaviour associated with stimulation of the cholinergic systems by nicotine may cause smokers to ingest more tea and coffee. The caffeine in tea and coffee can stimulate the central nervous system and this may increase energy expenditure significantly. In addition, the catechins and L-theanine in tea may act synergistically with the caffeine in tea to produce significant weight loss effects.
Another possible metabolic role for nicotine in weight loss is the stimulation of uncoupling proteins in both brown and white adipose tissue. Uncoupling proteins are responsible for uncoupling the energy pathways from the production of ATP, by instead wasting the energy as heat. Some evidence also suggest that nicotine could reduce long term body weight though increasing plasma levels of leptin, which in turn signals the hypothalamus to increase energy expenditure and decrease energy intake. In addition, smoking has certain behavioural aspects associated with it that could lead to weight loss. For example, smoking can alter the sensation of taste and smell and this may have a significant impact on feeding behaviour, perhaps lowering the palatability of certain obesogenic foods. Smoking may also initiate the termination of feeding behaviour. Smoking a cigarette for example after a meal may curtail further food intake, while non-smokers are more likely to continue eating.
Dr Robert Barrington’s Nutritional Recommendation: Smoking is bad for the health and is not recommended. However, it is clear that cessation of smoking is associated with weight gain. Those wishing to prevent this weight gain should eat a high quality diet and ensure that obesogenic dietary factors are eliminated during the adjustment period following cessation of smoking. A gain of around 10 lbs should be expected unless an effective strategy is in place to prevent this adjustment in body weight. Drinking tea and coffee may prevent reductions in energy expenditure on withdrawal of nicotine.
RdB
