I haven't really seen any studies addressing whether or not humans in a "lean" culture get fatter and leaner in a yearly cycle. I have seen something--I think it was in Gambian women? There was a sort of cycle of famine and relative plenty, I think caused by an agricultural cycle, and these woman had regular cycles of fattening and weight-loss. There can be yearly cycles of food availability even outside of agriculture--it's possible that this is the key in humans. It doesn't have to be strictly seasonal, as with hibernating animals. There was a study posted by Turtle a few years ago, I believe, where some mice were either fed ad-lib or fed 95 percent of what the ad-lib mice chose to eat. The 95 percent fed mice got fatter--but the difference in food intake might not be why. They were given the opportunity to eat much less food--this is what I think caused the weight-gain, if you can get what you need, but just barely, it might be time to set aside a little bit of fat for the future. Lack of "more than enough" can be a problem.
Eating nothing might not be worse (sometimes) than eating less. Eating nothing signals that you'd better cut into fat stores to survive, where eating slightly less suggests that even leaner times might be coming, better store fat.