In my late teens/early twenties, I did my own version of a very low-fat diet. IIRC, I didn't eat breakfast. For lunch, I would have a grilled cheese with dill pickles inside, but no butter on the bread. For dinner, I would have pasta with broccoli, onion and fat-free Italian dressing. Cold, usually. I lost some weight but amazingly couldn't keep it up for long. That's actually the only time I've really tried to lose weight, other than now.

My MIL told me that when she was in high school, for weeks she ate nothing but Cheerios, though she did take a multivitamin every day. It worked, but her mom was not happy with her.