For the short term,nicotine increases energy expenditure and could reduce appetite, which may explain why smokers tend to have lower body weight than nonsmokers.Nicotine lowers the set-point which can also be reason for the low body weight in smokers.But take care of this thing that smoking is not an efficient way to control body weight, and it does not help to prevent obesity, and could favor visceral fat accumulation and increase the risk of metabolic syndrome and diabetes.