While browsing the online Lancet website I came accross the following article.  A J-shaped mortality curve should come as no surprise.

The Lancet, Early Online Publication, 18 March 2009

doi:10.1016/S0140-6736(09)60318-4Cite or Link Using DOI

Editors’ note: Around the world, increasing body-mass index (BMI) is a major public concern. Rightly so, according to this international collaborative analysis of almost 1 million people, followed from middle age in 57 prospective studies. A J-shaped mortality curve is observed, with optimal survival at a BMI of 22•5–25 kg/m2. Above this range, mortality from several causes—especially vascular diseases—was increased. Moderate obesity (BMI 30–35) was associated with 3 years’ loss of life. People with extreme obesity (BMI 40–50) lost 10 years of life, equivalent to the years lost by lifetime smoking.