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