The good news: smoking is down dramatically, and people are much less likely to contract certain cancers.
The bad news: obesity is up, and researchers have been wondering why.
This may only be a correlation and not causation; but, the drop in smoking happened at about the same time as the rise in obesity. It isn’t clear whether that means smoking suppressed an earlier obesity trend that is only now becoming prevalent (because not all obese people smoked), or that means the rise in obesity is from the addition of many previous smokers. The correlation, however, does encourage additional study.
A more general lesson is that we live in a complex world and ideas that sound great on their own may be great, but they will also have unintended consequences. There’s always more work to do, sometimes just adjusting to the new circumstance.
(Click on the graph for the link.)