Based purely on anecdotal evidence, I would say "Want to Be Happy? Have regular bowel movements." Of course anyone with long term health issues will know that it's easy to let them run your life. Based on conversations I've had (especially with older people), having the toilet run your life is pretty common and debilitating, though. For me, it was complications from surgery (which have mostly sorted themselves out, it seems). Quick piece of anecdotal advice: 25 grams of dark (>= 72% cacao) chocolate a day works absolute wonders.