For today’s edition of Dear Mark, we’ve got a three-parter that’s really closer to a five-parter. First are a couple of questions from Joe, who first wonders about the hormetic benefits of acute sleep deprivation (are there any?) and then asks how he can beat a sweet tooth he suspects is brought on by lack of exercise. The second pair of questions concern CrossFit (is it an example of Chronic Cardio and should I be recommending it?) and breadfruit (does it have a place on the Primal eating plan?). And finally, Andy asks for the origin of the popular “gut is 80% of our immune system” statement.