Kefir (pronunciation here), is a wonderful, tart, milk-based beverage loaded with beneficial probiotics. The low-fat and non-fat versions have less calories than the whole milk kind. It is now widely available in natural and organic markets and many supermarkets, as well.
From Wikipedia, a bit more:
"Kefir (alternately kefīrs, keefir, kephir, kewra, talai, mudu kekiya, milkkefir, búlgaros) is a fermented milk drink that originated in the Caucasus region. It is prepared by inoculating cow, goat, or sheep's milk with kefir grains...
...Kefir grains are a combination of bacteria and yeasts in a matrix of proteins, lipids, and sugars. This symbiotic matrix forms grains that resemble cauliflower. Today, kefir is becoming increasingly popular due to new research into its health benefits. Many different bacteria and yeasts are found in the kefir grains, which are a complex and highly variable community of micro-organisms.
Traditional kefir is fermented at ambient temperatures, generally overnight. Fermentation of the lactose yields a sour, carbonated, slightly alcoholic beverage, with a consistency similar to thin yogurt. Kefir fermented by small-scale dairies early in the 20th century achieved alcohol levels between 1 and 2 percent, but kefir made commercially with modern methods of production has less than 1% alcohol, possibly due to reduced fermentation time.
Variations that thrive in various other liquids exist. They may vary markedly from kefir in both appearance and microbial composition. Water kefir (or kefir d'acqua) is grown in water with sugar (sometimes with added dry fruit such as figs, and lemon juice) for a day or more at room temperature...
...While some drink kefir straight, many find it too sour on its own and prefer to add fruits, honey, maple syrup or other flavors or sweeteners. Frozen bananas, strawberries, blueberries or other fruits can be mixed with kefir in a blender to make a smoothie. Vanilla, agave nectar and other flavorings may also be added. In Poland Kefir is sold with different varieties of fruit and flavors already added, both in the organic/ecologic and non-organic varieties. It is a breakfast, lunch and dinner drink popular across all areas of the Russian Federation, Belarus, Ukraine, Poland (second largest producer after Russia, Norway, Sweden, Finland (especially Russian and Estonian minorities), Latvia, Estonia and Lithuania where it is known as an affordable health drink. In Southern Slavic countries kefir is consumed anytime in the day, especially with zelnik, burek and banitsa."