Kefir is a cultured milk beverage traditionally made with cow, sheep, or goat's milk and the introduction of kefir grains.  Originating from parts of Southwest Asia, Russia, and Eastern Europe, Kefir's name comes from the Turkish word keyif, meaning "feeling good".  For centuries people groups have incorporated kefir into their diet in the belief that it protected them from chronic disease.  Starting with good quality milk and the addition of kefir grains as the starter culture, the end result resembles a tart drinkable yogurt.  Kefir grains have a similar appearance to cauliflower, but in fact are a structure of polysaccharides and protein that house a symbiotic matrix of friendly bacteria and yeast.  Consuming kefir is valuable because of the harmonious relationship of friendly bacteria and beneficial yeast that bring restoration to the inner ecology of those who enjoy it. 

Kefir is a probiotic powerhouse, with over 30 different strains of beneficial bacteria and yeasts.  In fact, it has far more strains of probiotic bacteria than those present in yogurt. The exact strains of bacteria and yeasts vary based on where the kefir is cultured and the conditions in which it was cultured.  The most abundant bacteria are numerous strains of lactobacilli. These microorganisms within the kefir grains produce antibiotics and lactic acid, which inhibits the proliferation of pathogenic microorganisms in kefir.  This environment keeps the good microorganisms flourishing and allows for a long shelf life of refrigerated kefir.  

In addition to probiotics, kefir has many enzymes which are crucial for digestion as well as biochemical reactions within the body. Kefir is high in several nutrients such as calcium, magnesium, folate, phosphorus, riboflavin, and Vitamin B12.  Also, kefir made from grassfed, full fat dairy is high in Vitamin K2 which is essential for calcium metabolism and Vitamin D3 utilization.

Kefir has been associated with a myriad of health benefits.  Probiotics present in milk kefir have been shown to colonize in the gut, bringing beneficial bacteria and balance to the gut.  Issues such as diarrhea, constipation, irritable bowel syndrome, inflammatory bowel disease, H. pylori infection, and other digestive problems can be treated and prevented utilizing probiotic strains present in kefir.  Kefir aids in cholesterol metabolism, blood pressure regulation, and supports the body's detoxification processes.  It is known to suppress tumors and has anti-carcinogenic properties.  Kefir also modulates the immune system which can bring relief from allergies and asthma.  Studies show that kefir can increase the speed of burn and wound healing.  Lastly, kefir has been found to aid in bone remineralization, making it wonderful for those with osteoporosis and osteopenia.

Kefir is usually well tolerated by those who are lactose intolerant.  Dairy foods contain lactose, which is a milk sugar and is unable to be broken down by many people.  Kefir has very little lactose left in the final product because during the fermenting process lactose is turned into lactic acid.   Additionally,  the enzyme lactase is present in kefir which is needed to digest any lingering lactose.  

To learn how to prepare kefir in your home, please see this post. 

Sources

https://www.ncbi.nlm.nih.gov/m/pubmed/22529959/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3833126/

http://ntur.lib.ntu.edu.tw/bitstream/246246/177589/1/04.pdf

https://www.ncbi.nlm.nih.gov/pubmed/25278298

https://www.ncbi.nlm.nih.gov/pubmed/22237053