Indeed; even if they can make lettuce grow, it's very low in nutritional value so they'd need to sacrifice a lot of space and energy into creating something edible. Potatoes would work better. Space pigs, too, but they'd require a lot of nutrients to keep alive and grow. iirc they need ten times as much food than what their meat is worth in nutritional value.

The future is probably artificially produced food, like the porridge / sludge shown in the Matrix. Something out of a chemical process instead of a biological one.