Eat and drink even more. I was drinking at a pond about 35 times and eating about 5 (or even more) cans of beans until i finally got the 'healing' tag and soon the 'healthy' tag. So just eat and drink until you get the messge my stomach is full. I think you also must not be injured or be sick. Well kinda hard to find out all this stuff with no HUD. But, I like.