Seriously, that should be my answer to everything
Here's my opinion tho: If you wanna get the best outta working out, you gotta eat healthy. You should eat even though you don't have the appetite. Eating is super super super important foo. If you don't eat for long periods of time, your stomach will begin to shrink. And that means you won't be able to eat much anymore. And that's scary. You have to gradually eat more food over time. Eat small snacks. You also want to consume a variety of food to get your body back into shape. I know this sounds weird, but eat with bigger cups. Sometimes it makes you wanna eat the whole thing. But if not, eat in small portions. Also, drink caloric juices if you don't feel like eating as much. Once you begin to fatten up, change the fat to muscle by working out. It's not as easy as I put it tho.
But good luck