However, it is not quite that simple.
A retrospective cohort study of 10,692 adult smokers with type 2 diabetes that used the Health Improvement Network, a large UK primary care database, found that smoking cessation is associated with a deterioration in glycaemic control that lasts for three years and is unrelated to weight gain.
The tiny additional risk of microvascular events that this might cause does not of course cancel the enormous cardiovascular benefit of smoking cessation.
Lycett, D., Nichols, L., Ryan, R., Farley, A., Roalfe, A., Mohammed, M.A., Szatkowski, L., Coleman, T., Morris, R., Farmer, A. & Aveyard, P. (2015) The Association between Smoking Cessation and Glycaemic Control in Patients with Type 2 Diabetes: A THIN Database Cohort Study. The Lancet: Diabetes & Endocrinology. 3(6), pp.423-430. doi:10.1016/S2213-8587(15)00082-0.