Fermented products such as kefir are considered functional foods because they offer enzymes, pre-digested nutrients, amino acids, vitamins, minerals, calories/energy and billions of probiotics. Probiotic pill supplements contain just one or a select variety of bacteria, and usually that's it. It's always better to eat something in its whole form when possible, because each part makes the other more digestible. This is why companies are now adding fiber back into cereals and fruit juices, and citric acid into calcium - you often need all the parts to assimilate nutrients correctly.

 

source:  http://www.yemoos.com/faqwahealth.html