Eh, dudes in prison don't drink "brewers yeast". morons... goddamn pretty boy morons. puff-daddy's of youtube bbing.
guys in prison get big because
1-many have never lifted weights before coming to prison and had no idea they had the genetics to carry muscle
2-we don't burn many kcals. we get up, go to breakfast, come back to the bunk and laydown before count, get up and get ready for work (which is sitting down, usually, unless you work in the kitchen or construction)... come back to the bunk, count... go to chow... come back to the bunk.. count... go back to work... come back to the bunk.. chow... ect ect ect....... 50% of your day is laying down in your bunk watching tv and eating whatever snacks you can afford.
3-we get egg's and milk for breakfast, and 3 meals a day with decent kcals (starch mostly). we'll trade whatever we can for protein foods, whether in the chow hall or stolen kitchen goods. we'll buy tons peanut butter and if we can, powdered egg's stolen from the kitchen.
4-many prisons have only freeweights and the ego's make them/us lift as heavy as possible. lots of squats, mil press, weighted chins, bench press, db rows, ect...