I have no idea other than the pittance you get from swallowing or buying and the very rare food cache. I even have the perk for foraging but I have no idea how to forage, I've never seen a prompt. On the android version.
Ways to get food: 1. Food caches. There will be more of them if you have high Perception (scout 3) all the time. But luck also plays its part.
2. Sleeping in an inn. Costs 10 gold, gives you 42 food. Knowing where to get money, you can just sleep multiple times, and you certainly will have enough for your journey.
3. Various encounters. If you win against a Centaur, next time she lets you eat with them, and gives you even more food if you defeat her. Arachne has some food if your Perception is 6. If you meet Flocking Harpy and have Agility 8 you can steal 40 food each time. After passing the second map, Sleeping Ettin can provide you with 40 food if you're Agile enough.
4. Foraging also is a way, but it's emergency. It happens only when you reach 0 food in the overworld. You find a way to get more food, but this isn't worth counting on.