Re: Oh, another question, is Kefir a good source of protein versus whey?
As a protein source kefir is probably equal to the protein in the milk that made it. If by WHEY, you mean the powdered CONCENTRATED whey protein (like the health food stores sell) then the WHEY has FAR more protein, sometimes 90% by weight.
Figure kefir for about 8 grams of protein for every 8 ounce glassful, unless it's fortified with extra powdered milk commercially.
Both have identical amino acid compositions and are both "complete" proteins.
Of course only the kefir has the plethora of probiotics (many MANY more kinds than yoghurt...and many that survive into the intestines!)