I admit to not having read the study, but I am always suspicious of any testing on Norway Rats. Their metabolism is different, they cannot vomit and they have no spleen.
They are very social creatures, will raise and feed each others litters, and in the wild will also bring food to sick or elderly members of the group who cannot feed themselves.
Unlike humans, rats are opportunistic scavengers, happily consuming carrion, old bones (their back teeth grind everything into a powder before swallowing) and will happily and regularly eat their own dead as naturally as they would eat dandelions or hunt insects.
Edited to add that pregnant rats under stress will reabsorb their litters. Low resources means no more babies and/or younger low ranking animals are evicted from the community. If you see a sleek rat in the daytime, it's been excommunicated and undertaking very risky behaviour to eat.
I really don't believe that fasting is in any way a natural state for rats. The study can only show what happened to severely stressed animals (one can only surmise they were kept in solitary confinement to stop fighting, injuring and eating one another) in an unnatural environment testing something their metabolisms were never meant to cope with in the first place.
Better idea: let's study this in humans. It would never be as clinically excellent as any study on captive animals, and would certainly prove far more difficult to fund but it would at least be relevant to our own species.
