Except that human civilization has been grain based for millennia. (Indeed, contrary to the "paleo" fad, grain consumption goes back to the days of Neandderthals; our gatherer-hunter ancestors gathered wild grains.) But traditional agricultural societies didn't see the sort of obesity crisis we see in industrial societies. Industrial societies are marked by high sugar consumption -- particularly in the past few decades -- which can led to general overeating, as everything becomes sweeter and more palatable. (Note how the title jumps right over the sugar to noodles.)
Industrial societies are also marked by sedentary lifestyles.
Overeating bad. Sugar bad, Meat bad, though the flesh of free-living wild animals is somewhat less bad than industrially-raised animals bred for generations to be fat. Dairy bad. Highly processed industrial food products bad. Grains ok if not over-processed; weight towards whole grains and heirloom varieties. Vegetables good. Legumes good.
And exercise good.