Kefir is an ancient drink that originated in Russia. Similar in taste to yogurt, kefir is made from fermented milk and is slightly sour. Its popularity has soared in recent years because of growing interest in probiotics, which are known to boost the immune system and support good digestive health. Find it in the refrigerated aisle at your local supermarket or health-food store.
Available at supermarkets, health-food stores, and online; try lifeway.net.