Multiple sources point to happiness and a general lack of bad stress being good for your health. One of the most glaring commonalities of the longest lived cultures in "The Blue Zones" was their tight community that valued older members. Not sleeping enough or being overly stressed raises cortisol levels, as well as increases other undesirable hormones.
Is it possible that the meat from animals that lived particularly stressful lives (think factory farmed chickens living in cages covered in albatross shit) could retain those hormones? If artificial hormones given to animals can lower the meat's nutrition, couldn't it be the same case for natural hormones?
Not that there isn't enough problems with factory farming to avoid it all together as it is, but it'd be nice if one could argue that treating animals well isn't a selfless treehugger-esque act, but routed in science and as practical as it is moral.
Alex, Co-Founder of PaleoPax.com