Fasting
As far back as childhood I suspected that hunger was a motivational tool, but I figured that the reason was due to a promise of future reward. However, it appears that there's a more literal and studied effect at play. When a living creature has easy access to food and nutrients, the body endorses cellular growth and reproduction. However, under harsh conditions the activity shifts towards cell maintenance and protection (Levitin). There's a passage by Cynthia Kenyon that I like so much I will reproduce it in full below:
Slowing aging might seem like an overwhelming challenge, as the decline is so pervasive. So it is noteworthy that when we extend the lifespans of laboratory animals, we do not have to combat individually all the problems of age, such as the declining muscles, the wrinkled skin, and the mutant mitochondria. Instead, we just tweak a regulatory gene, and the animal does the rest. in other words, animals have the latent potential to live much longer than they normally do.
Caloric deficit, it seems, is the simplest and safest way to induce this shift in biologic priority.
Aside from, perhaps, extending one's lifespan, caloric restriction may unlock other abilities. Evidently both caloric restriction and exercise "stimulate the production of brain-derived neurotrophic growth factors (BDNF's). Fasting stimulates the production of ketones, an energy source for neurons. Fasting can increase the number of mitochondria in neurons, which helps them produce more energy" - Levitin. In short, the brain works better when the body is hungry.
It's not yet certain whether general hunger, intermittent fasting, or full-fasting is most effective at inducing this effect.
It is my intent to run this experiment on myself at some point in the future. I'll document that work here.