I'm sorry maybe it's a bug and I'm gonna google it out, the idea is that when you press the eat button, you'll randomly get any of three foods, hotdog, gives +50 food +10 happy, the banana which is neutral is +30 food and the eggplant that gives +10 food but it makes you dirty -10.
I test it out and the eating feature works (just animation bugs) and the hungry bar fills it up, maybe you are confusing it with the happy bar which is the first one which it fills up with the TV and the Swimming pool buttons, the order might be confusing since they don't match at all.
Thank you for you comment!