Self-Eating (Autophagy) an ancient process involved in repair & aging, switches on while fasting and is exquisitely sensitive to dietary glucose abundance.
The tools of the “blind watchmaker” (Richard Dawkins on evolution) are serendipity and improvisation. The first lesson in order to uncover the secrets of biology is to recognize the untidiness of it all, where mechanisms for doing one thing are borrowed to do another and the process repeated ad infinitum; if it works after a fashion, at least to get to the point of sexual maturity then all the better but after that he could care less, however after maturity the human condition involves 70 years or so of decline and unraveling the idiosyncrasies of the blind watchmaker may turn up some benefits to our fragile existence.
This is how I view the evolution of autophagy over a billion years: A process that worked to preserve the life of single celled organisms when dormant and starved of nutrients has evolved to become a complex and lethally indispensable process for the existence of any form of multicellular animals. Funny that autophagy is unknown to most doctors, its discovery is so new, but its untidiness and improvisation is evident from the numerous overlapping functions it fulfills. While fasting it provides glucose and fatty acids for energy and amino-acids for assembly of vital new proteins but simultaneously fasting likely improves autophagy’s other improvised roles; it detoxifies cells and stops them gumming up, regulates recycling, healing, repair, cell turnover, immunity and inflammation. The exciting thing for us is that this vital process is eminently amenable to regulation through lifestyle choices such as exercise and nutrition. Differentiating between fasting and feasting is critical to survival and a barometer of this switch is the level of glucose in blood and extra-cellular fluid, just 10 grams: a tiny amount compared to energy demands which, if supplied by glucose alone could vary between 0.5 grams per minute at rest to 5 grams per minute while running (clearly 5g per minute form a pool of 10g would be rapidly unsustainable). This delicate sensitivity of blood glucose to feeding argues that glucose is a barometer of energy status and not our primary energy source, this role is reserved for fatty acids of which we carry hundreds of thousands of Calories in our 10-20% plus body fat. The molecular signaling pathway of this pivotal role of blood glucose is becoming clearer; simply restricting blood glucose reverses the ratio of insulin to glucagon that controls the activation of mTOR that in turn regulates autophagy and numerous other things that influence aging and age related diseases that are now the commonest causes of death and disability,