There are so many different types of probiotics out there that I won't even begin to list them (like HSO's and acidophilus). As a basic defintion, probiotics are used to bring a balance between the good and bad bacteria in the intestines.

You can take probiotic supplements or eat probiotic foods (foods that naturally have active good bacteria in them like unsweetened yogurt and lactic fermented products). There is much controversy over which ones work and which ones won't. I find that if my stomach is doing ok, yogurt won't hurt me. Does it HELP me? Couldn't say for sure, but it's a good food that satisfies my snack cravings and replaced cereal in my breakfast ritual.

Which reminds me: trying to up your good bacteria and fight the bad bacteria in your gut by eating yogurt? Great, but if you're eating sweetened yogurt, you're eating sugar which feeds the yeasties.

One problem with probiotic supplements is that the armies of good bacterias in the pill or powder have to be alive and STAY alive during the trip to the small intestine. Most of them are dead before you even take the pill.

In Restoring Your Digestive Health by Rubin and Brasco (1993), a sort of test is suggested that will give you an idea whether or not your probiotic has enough living bacteria to make a difference. They say to "drop a few caplets into 2 or 4 ounces of milk and let the milk sit at room temperature for 24 - 48 hours...If the probiotic supplement is viable, the milk will curdle to a thick yogurt-like consistency."