The body eats itself to survive. Only as a last resort but still the body has the capacity to breakdown and consume itself for energy. The internal process is called catabolysis and happens once all other resources within the body have been completely depleted. There are times when the body is low on energy and will use muscle or fat throughout the body for short term energy however those are stopgaps until the next meal is reached. The internal solution to take from an energy store that makes something else function well is self contained and immediate. The process is distributed across the body as well based on the areas that can bear it most.
Bodies die of survival when no meal can be found and energy stores within disappear. The other end of survival dynamics in the body is filled by cells going rampant and spreading outside of the balance set within and across the rest of the system they inhabit. A new balance can not be reached in many cases and the whole does not make it through the unrestrained expansion of the few within. Times of low resources might lead us to expect cancers to abound in a body with the strongest parts expropriating resources from the rest. It is during these times of struggle however that the body consolidates function and refines needs. What would results for incidence of different internal disease such as cancers show about the affect of access to food, diet, and substance habits if income, access to health care, and education were controlled within the study.