wait a sec - Doshas aren't fads! they ARE the thousands of years of empirical knowledge. :) People just tend to apply them too strictly is all. As general guidelines they're very effective. I still eat broccoli, I just know it will give me gas so I'd better eat it as soup, never raw. ;)
But yes, looking back over time is how I like to do it too - if any fad says this is bad or that is good, I look at what's been done for centuries and see if it's there. Like that "olive oil is bad" post. Olive oil has been around for centuries. It's okay in my book! :)