Henry is a man of flesh and blood and so he must eat and sleep to survive and stay fit.
The opposite to hunger is overeating. Stuffing yourself like a pig has the advantage that you won’t need to eat for longer, but a full belly will slow you down and, like with hunger, your Stamina will regenerate more slowly.
You can see whether you need to eat in the Player tab under the picture of Henry in the Nourishment stat. You can see whether you’re hungry or overstuffed not only in the Buffs tab, but also from the icon next to your health indicator:
You also need to watch what you eat – if you eat or drink something that’s spoiled, you can get food poisoning, which you can only cure by taking Antidote potion. You can tell you’ve been poisoned by the icon next to your health indicator.