Why do the microwave and frozen dinner inexorably lead to obesity? According to the economists, the cheapness of calories (both in terms of price and time) has led us to dramatically boost consumption. Food stops being something we make and create—it doesn’t require very many lever presses, so to speak—and becomes something we simply ingest. Eating just gets easier. And then we get fatter. ... Maybe this is why Americans need ever larger portion sizes: Because we didn’t make the milkshake ourselves, because that dinner only required a few minutes of work, we need to consume more calories to get the same baseline of satisfaction.