Maybe their improved functioning was a result of them being removed from environmental toxins. I imagine in the Biosphere there level of physical activity was a bit like light gardening, rather than even an aerobics class..

There is a ton of evidence to support humans survivability, nay even thrivance on almost no food (it's called history). I'm just coming from a standpoint of optimization. Living longer is a kind of optimization, as is exercise adaption, as is learning

I'm all for self-experimentation of almost any kind, but the weak link in their arguments is nutrition, so it's just something to keep an eye out for. Tho, it's not likely you'll be contracting Pellagra any time soon.