> The problem is, most scientists say "We have evidence today to suggest ..." and most average-joe's hear "This is the absolute truth and everything else is wrong".

Well, the problem is perhaps more precisely that scientists say "We have evidence to suggest...", and then marketers and propagandists say "It is proven that...", and that "Average Joes" mostly never hear what scientists say, only what the marketers and propagandists say.

That's true.

It's also true that diet et al. are actually hard problems. We're dealing here with complex systems. It's not easy to find optimal answers, assuming such answers even exist.