We already do eat vat-grown stuff. And I'm mostly talking about staples, which make up the vast majority of farmland. For anything mashed or made into flour or oil or powder, there's basically no fundamental difference between it being made in a vat versus a field. Whole, unprocessed vegetables like lettuce, etc? Well, that corresponds to a small fraction of farmland, and it also grows great hydroponically. Don't need to grow that in vats.