During the Paleolithic period of man's evolution there were little or no auto immune diseases, obesity, depression, heart disease, diabetes or healthcare problems other than death caused by natural enemies such as viruses, large predatory animals, and sickness because we didn't have antibiotics or medicine. We moved constantly (except after catching a large animal to eat, we would lay around for a few days gorging) ate fruits that were in season, roots, bugs, nuts, seeds and some vegetables. We were often in a state of Ketosis where we subsisted on nothing but animal protein and fats because during the winter months there weren't any fruits or veggies. We climbed, sprinted, lifted, and we were very lean. This is the approach I take in designing workouts, nutrition and lifestyle. Our immune systems were much stronger and adapted to more stressful conditions. Today, if we're cold we turn up the heat, if we're hot we turn on the air conditioning, if we're hungry we eat (mindlessly and bad foods). But if we're in need of sleep we often don't and when we should be moving we're often sitting watching tv, our cell phone, computer or driving. This combination of being sedentary and eating refined grains is the real cause of heart disease, depression, auto immune diseases and a lot of cancers. And STRESS!