Interesting. This research suggests that a diet rich in fish could improve leptin sensitivity.
Just my take:
Could it be that fish could have this effect on humans because if grok and his tribe were to live by a lake/river etc. there would be a much more stable supply of food than if we had to go out and hunt which wasn't always successful? A diet rich in fish could signal to the body that there is a reliable source of food and thus increase leptin sensitivity decreasing appetite and ultimately that less body fat needs to be stored.
Any thoughts? Quite interesting this whole leptin thing!