Think about our ancestors. They typically started to gain weight late summer/fall (when fruits, nuts, etc are plentiful) so they would have an energy store for the lean winter months. They would be back to their "normal" weight by spring and could eat regularly as spring and summer moved on. But a weight gain during early summer would have no benefit. I bet that it is "built in" for us to have decreased appetite late spring/early summer when eating extra food would not be critical (maybe even have a negative effect in the efficiency of the hunter-gatherer lifestyle). The warming of spring/summer could be the trigger to lose appetite and maybe the chilling of fall could trigger an increase in appetite.


Just a thought. (Too many genetics and ecology courses on my transcript....)