Actually, I think the reality is more nuanced than that.
It's not about fads or conflicting findings; it's that many things are beneficial in some ways and harmful in others. Biological systems are massively complex, after all.
So it's not surprising that we get studies that say, for instance, that coffee lowers blood pressure but also causes bone demineralization, or that caffeine protects against Parkinson's disease but also has toxic effects on the liver. Few things are entirely good or entirely bad; many things benefit one system but hurt another. There isn't a contradiction there.
