There is evidence. The CCHS, the Canadian community health survey, had very good evidence because they looked at socio-economic status at the same time. Interestingly enough, men in higher income levels actually have higher rates of obesity, which is quite surprising. Women in the middle-income area tend to have the highest rates of obesity. But if you look overall, folks with less than a high school education have higher rates of obesity than folks with more than high school education.
On September 21st, 2006. See this statement in context.