Kefir

[Clodfobble]

You don't have to do it yourself, you can buy commercially-made kefir that's as safe as, for example, commercially-made yogurt. (The drawback being that it has about the same probiotic content of commercially-made yogurt, which is a tiny fraction of what the 24-hour fermented product you could make at home will have.) Nowadays you don't even have to go to Whole Foods, you can probably find it at your regular grocery store.