Considering how (relatively) poorly most modern Americans eat these days, and the chemicals, pollutants and medications that enter our bodies, my personal feeling is that pretty much everyone (and their dogs!) should replace or boost their intestinal flora/fauna at least weekly, with a couple of tablespoons of really high- quality yogurt with multiple organisms, or kefir, or a pro-biotic cottage cheese, etc. And there are also liquids, powders and capsule forms of these available, some lactose-free, for those who hate yogurt or can't tolerate milk products.