I keep thinking of something I read about how if you want to boost self-esteem, you should take esteem-able actions. What makes you feel good? When you're feeling bad, you might be ready to wallow and make yourself feel even worse, but what if, without over analyzing it, you did one thing to make yourself feel better? A hot shower or a morning walk can change the course of my day.
When I started backing away from obsessive thoughts about diet and exercise, "Who am I without it?" was too big to ponder. I had nothing. If you've neglected other interests for years, it's not obvious. You can't tick off a list of other things you're excited about or invested in. A place to start is, "What am I curious about?" So, things you might like to learn more about or pursue. If that is still crickets, "What was I excited about as a child?" Reading a book about a new interest, taking a class, or volunteering can help to expand your horizons and give you something else to focus on and feel good about. Then you start to get a greater sense of who you are and what is important to you. Eating as little as possible was a lame hobby, it turns out. Plenty of other pursuits are more fun and make us feel excited and connected instead of isolated and anxious.