Check out this interactive chart. It plots changes in average BMI across the globe. A few things to note about changes in the average BMIs. They have been increasing almost universally, though the variance in the rates of increase are large. They have been increasing disproportionately among women*.
* After playing through the data, hover over one of the bubbles to see the "trails" of the countries. Notice that most of the trails have a slope which is steeper than the 45 degree line, ie steeper than 1.