The consensus seems to be yes. Fermented milk products contain so-called “probiotic,” or “good” bacteria, including lactobacillus, acidophilus and bifidobacterium that compete with Candida in the vagina. Candida is a common yeast found in our colon and in women's vaginas. It can overgrow if healthy bacteria are killed (when taking antibiotics) and lead to a yeast infection. The probiotics found in yogurt are thought to counter the growth of Candida. That is considered a desirable effect.
In a Finnish study conducted of 320 women, researchers found that those who ate three or more servings per week of yogurt, or in some cases cheeses made from fermented milk, had far fewer UTIs than those who didn’t eat yogurt or ate it only infrequently.
Several studies have found that to cause a significant reduction in the occurrence of yeast infections, people need to consume at least one serving of yogurt per day. In these studies, the yogurt contained acidophilus bacteria, which is generally noted on food labels as containing “live” or “active” cultures.
Half of all women will experience a yeast infection in their lifetime. Women who suffer from repeated infections may want to add yogurt to their regular diets and have at least one serving daily. Because yeast feeds on sugar, most researchers recommend choosing low sugar or unsweetened yogurts.
Once you have a yeast infection or UTI, you must take antibiotics to treat them- yogurt will do nothing for an active infection, but it can help prevent them.
-Matthew E. Karlovsky, M.D
Female Urology & Urogynecology blog