An article about two years ago in National Geographic
on the life of Orangutans (I think) had a nifty
graph of the ketone levels in the Orangutan's
blood throughout the year.  They go through
a yearly cycle.  They fatten up when fruit is
plentiful, and thin down when it is not.  Their
reproductive cycle is in sync with this so they
reproduce at the peak of the fat cycle.

I assume a HG goes through the same cycle.

R. Keene