Surviving the test of time is the ultimate empirical evidence. In fact I'd go so far to say it's the ONLY way we can test the truth of anything at all. This goes for anything, from biological systems (evolution), technical design - the wheel, to research papers. Look in your fridge: most of the food there has been consumed for thousands of years using basically the same cooking method and is for the most part considered healthy. The recent synthetic foods like margarine and recent cooking methods like deep frying are detrimental to health.

Keep in mind, practiced over 'x' amount of time where x > 2000 years.