I lived in one of those food study centers after college. Most people there were pretty diligent about sticking to the program, but there was a big scandal when one guy was kicked out after discovering extensive cheating and several papers had to be retracted.

We were allowed out - I had a full time job, but couldn't eat or drink any food not provided by the center (we took a radio-isotope tracer with food, and had to collect our poop). It was quite interesting :_)