While I agree that longevity may not be a good indicator of overall health, I always have to laugh when I see this argument. It simply fails the most basic test of logic. If you go back 500 years you'll find that life expectancy was something like 40 years, which, for one thing, means that most people did not live long enough to experience many of the health problems that plague us today. Sure, even today, there are some cases of heart disease or stroke or cancer that show up relatively early in life. But the incidence of those problems is much greater at ages that were rarely reached prior to the last few hundred years. If most people don't live long enough to suffer from heart disease, you're not going to see much heart disease, whatever the cause.

The diet of medieval or renaissance man may have been healthier than today's Western diet (all things considered, I rather doubt it), but the absence of heart disease, et al doesn't prove it.

To see the fallacy of this argument in a clear light, consider an equally ridiculous hypothesis: Relatively few people died in traffic accidents 500 years ago, therefore we can conclude that traffic laws were better, vehicles were safer and people were better drivers way back then. Logical? Not hardly.