Smoking may increase abdominal obesity

Smokers who believe their habit to be a way of controlling weight may have to think again. New British research shows that people who currently smoke had higher waist to hip ratios and bigger waists than former smokers and people who have never smoked (Obesity Research 2005;13:1466-75).

The researchers, who studied data on 21 828 men and women from Norfolk aged 45 to 79, say that smoking habits seem to influence patterns of fat distribution.

The paper says, “Although smoking is associated with lower body mass index (BMI), its relationship with increased abdominal obesity may reflect the metabolic consequences of smoking. The demonstration of these negative effects on body composition may go some way to reversing the belief that smoking is an effective strategy for weight control.

“Given the association with abdominal obesity, which is closely related to adverse metabolic outcomes, it is clear that smoking cessation and avoidance of smoking commencement remain key public health messages.”

The authors, from Cambridge University and the UK Medical Research Council, used self reported questionnaires to study smoking habits and other lifestyle factors. Body measurements were taken during physical examinations.

The results show that after adjustment for age, BMI, alcohol intake, total energy intake, physical activity, and level of education the waist to hip ratio was highest among current smokers and lowest among people who had never smoked. Current smokers had a higher waist circumference and lower hip circumference than former or never smokers.

The results also indicate that people who have smoked heavily or for a long time may need a longer period of smoking cessation than other smokers before they bring their waist to hip ratio down towards that of never smokers.

The authors say that smoking habits seem to have an effect on fat distribution: “Although smokers have lower mean BMI compared with non-smokers, they have a more metabolically adverse fat distribution profile, with higher central adiposity.”

They add, “Central adiposity, which reflects visceral fat deposition, seems to be a better indicator of the adverse metabolic consequences of obesity than overall adiposity. Additionally, weight loss associated with smoking may be caused by a reduction in lean mass rather than fat mass, which BMI may not fully differentiate.”

Just why smoking should have an effect on fat distribution is not clear. One theory is that smoking has some kind of anti-oestrogenic effect. Another suggestion is that cigarette smoking may have an effect on the uptake and storage of triglyceride fatty acids, increasing fat mass.

The authors say that the explanation for the association may help identify the mechanisms underlying the adverse health consequences of cigarette smoking and abdominal obesity.