Yogurt is a fermented dairy product. Most of you probably buy it made from cow's milk, but its tangier cousin, goat's milk yogurt, is also available. I bought this cow's milk yogurt from the farmer's market on Wednesday. It tastes so much fresher than the store bought kind, since it comes from cows down the road.
Yogurt is made by adding bacterial cultures to milk. These cultures–like Lactobacillus and Bifidobacterium— convert milk's lactose to lactic acid. This gives yogurt its tangy, sour flavor. Those that are lactose-intolerant can tolerate yogurt more than milk, because the cultures produce the enzyme, lactase, that digests lactose.
Yogurt is rich in protein, calcium, riboflavin, phosphorous, B12. The live cultures in yogurt help with digestion. They also maintain healthy intestinal flora and suppress the harmful bacteria. Some studies even link yogurt consumption with lower rates of colon cancer.
Plain yogurt is the best choice. It's lower in sugar than the fruit flavored versions. Most of the fruit versions contain a lot of sugar. Buy organic, so you don't have icky artificial additives, hormones and colors in your food. If you can't stand the taste of plain, add a bit of honey and cinnamon.
Source: Murray, 2005, p. 589-91.