Yogurt is made by adding two probiotic bacteria to milk. The bacteria break down the milk's sugar (lactose) into lactic acid, which makes the yogurt more digestible for people with lactose intolerance. Many believe that the bugs also replenish your gut with healthy bacteria after you take antibiotics, but the evidence is scant. To establish a good crop of probiotics in the gut, the bacteria have to first survive the strong acids of the stomach and the bile salts of the small intestine. Pre-biotics are non-digestible food ingredients (found in insoluble fiber) that act as "food" for the probiotics.
The effects of probiotics are "strain specific;" there are dozens of strains and they can differ in what they do even within the same species. Only a small number have any proven benefits. Unfortunately, companies do not have to disclose which strains they put into their products.
As of yet, there is no evidence that yogurt, teas, or any "clinically proven" probiotic product will relieve irregularity or irritable bowel syndrome, cure autism, prevent a yeast infection or a cold, stop gas or bloating, prevent a UTI, or help you feel slimmer and more energetic.
Yogurt IS an excellent source of calcium and a great low fat snack, however. Just don't expect it to change your life.
~ CSPI, 2010