 The story of life on earth is a story of starvation ash from massive volcanoes and asteroids block out the sun, killing the plants which then killed most everything else. As Darwin pointed out, though, from this war of nature from famine and death, the most exalted object that we are capable of conceiving arose, namely us. We are particularly well adapted to prolonged fasting, evolving in a context of scarcity, is believed to have shaped our exceptional ability to store large amounts of calories when food is available. Of course, now our ability to easily pack on the pounds is leading to modern diseases like obesity and type 2 diabetes. But without the ability to store so much body fat, we may not have made it to tell the tale. And it's not just asteroids millions of years ago. All of Upper Egypt was dying of hunger. Read an inscription on an Egyptian tomb from about 4,000 years ago to such degree that everyone had come to eating his children. Or just hundreds of years ago, parents killed their children, and children killed their parents and ate them. The bodies of executed criminals were eagerly snatched from the gallows, wiping out as many as two-thirds of the population of Italy, one-third of the population of Paris. So we don't have to go back to ancient history, even the most secure and affluent populations of today need only trace their history back a short distance. For example, nearly 200 famines in Britain over the last 2,000 years. Now, we tend to be suffering from too much food, which carries its own problems. But might there be any negative consequences to not ever starving? This was a question raised 50 years ago. I mean, if our physiology is so well tuned to periodic starvation, maybe by eliminating that we may be doing harm to our overall well-being? We just didn't know. The lack of research in the area of starvation was attributed to the difficulty of securing willing human subjects. So what little we had came from unwilling subjects. Physicians within the Warsaw Ghetto made detailed accounts before they themselves succumbed. Or Irish Republican prisoners starving themselves to death after up to 73 days on hunger strike. But starvation isn't necessarily the same as fasting. An issue raised in medical journals over a century ago. Starvation is normally a forced, mentally stressful, and chronic condition, whereas therapeutic fasting is voluntary. Limited duration and usually practiced by people who start out with adequate nutrition. Therapeutic fasting? Where did we get this idea of fasting therapy? Fasting for medical purposes. Well, it may have originally rose out of the observation that when people get acutely ill, they tend to lose their appetite. So maybe there's something in the body's wisdom to stopping eating. That's presumably where the whole starva fever folklore came from. There was the sense that fasting forwards physiologic rest for the body, not just the digestive tract, but throughout, allowing the body to concentrate on healing. It was evidently an open secret that veterinarians used to hospitalize dogs only to fast them back to health. And so maybe, the theory went, it might work for people too. Beyond just freeing up all the resources that would normally be used for nutrient digestion in stores, there's this concept that during fasting our cells switch over to some sort of protection mode. Why would fasting reduce free radical damage and inflammation and bolster cellular protection? It's the that which doesn't kill us and makes a stronger concept known as hormesis. So that's kind of the opposite of the let the body rest theory. It's more like let the body stress. The stress of fasting may steal the body against other stresses coming your way. This was demonstrated perhaps most starkly in a set of cringe-worthy experiments in which mice were blasted with Hiroshima-level gamma radiation sufficient to kill 50% within two weeks. But of the mice who had first been intermittently fasted for six weeks before, not a single one died. It's this kind of dramatic data that led to, you know, extraordinary claims like therapeutic fasting could drive half of all doctors out of business. But you don't know until you put it to the test, which we'll explore next.