Increased bodyweight after stopping smoking may be due to changes in insulin secretion

Dr. Marietta Stadler, from the Hietzing Hospital in Vienna, Austria, enrolled healthy smokers on a smoking cessation programme into a study in which they underwent three-hour oral glucose tolerance tests (OGTT) while still smoking and after a minimum of three and six months after giving up. Their body composition was also measured at the same time. The researchers measured beta cell [1] secretion of insulin both while fasting and after exposure to glucose, and also looked at appetite levels in the participants by offering them a free choice buffet meal. In addition to insulin, fasting levels of a number of hormones involved in regulating energy intake and appetite were measured.

"We found that body weight and fat mass increased after three months of no smoking, by 4% and 22% respectively," said Dr. Stadler, "and after six months the increase was 5% and 35% respectively. The most striking metabolic findings were an increased first phase insulin secretion in response to glucose challenge, as well as increased carbohydrate intake in the free choice buffet after three months of non-smoking. Participants showed significant fasting insulin resistance, where the normal response to a given amount of insulin is reduced, at three months, but not at six months, while dynamic insulin sensitivity (the sensitivity to insulin in the postprandial state) assessed during the OGTT remained unchanged throughout. Neuropeptide-Y (NPY) [2] levels at fasting were increased at three months, but not at six months.

"We believe that the alterations in insulin secretion could possibly be related to the increased carbohydrate cravings and weight gain experienced by many smokers who give up. However, the increase in insulin secretion and carbohydrate intake seems to be a transient effect of stopping smoking, as these changes were not seen any more after six months, even though the participants had gained more weight."

Increased insulin secretion at three months was less pronounced in those who finally succeeded in quitting smoking for at least six months, as opposed to those who relapsed after three months. "All these factors are pointers to understanding the metabolic processes involved in weight gain after smoking cessation," said Dr. Stadler. "The more we can understand the biological basis for the phenomenon, the higher our chances of being able to control it."

The researchers now intend to match a group of non-smokers of the same age and body mass with the participants of this study in order to see whether, in comparison to non-smokers, beta cell function is altered in those who are still smoking and not just during the period when they are quitting.

"We also intend to discuss our results with experts in the field of addiction and behavioural medicine in order to gather ideas and hypotheses as to why smoking might exert these metabolic effects, in order that we can plan studies that bring together the many disciplines involved in this important field of research," Dr. Stadler concluded.