I really doubt that the yeast has anything to do with it. They GROWW in prison because they train, eat, and rest. ALOT of rest. Think about it, every inmate has a minimum of one hour of a rec a day, certain work details like cadre and kitchen workers get more, but an hour is enough to get in some good lifting. Then there's the food - in New York you can receive up to 35lbs of food(not including drinks/drink mixes) a month in the mail and packages whenever someone comes to visit, then you have commisary every week where you can spend $75+ on food that is very very cheap, thats the food deal not counting the 3 meals you get a day(and if you are working in the kitchen you basically have unlimited food). Now once you're done with work(which is minimal or non-existant if you aren't cadre or in the kitchen), rec(1 hour), and programs(GED classes, anger management, rehab, etc. 1-3 hours) you now have the rest of the day to just lay up in your cell or the tiers common room and this is the big secret...REST, REST, REST. I think that just about sums it up.