This isn't just about food, but look at the number of people one farmer could feed 200 years ago (6 or so) vs today (150 or so). We spend a lot of our productive time today doing stuff we didn't have time for just a couple hundred years ago. We've got a long way to fall before we are unable as a species to meet our needs. Proponents of tech advances expect our productivity to increase even if the workforce shrinks. If our standard of living delines on average, either these prognosticators are incorrect or we have a huge allocation issue.