What is your BMI? When someone wants to lose weight, I usually recommend between 1200 and 1500 cal a day and not be hungry. If you can manage 900 cal a day and not be hungry and eat a relatively diverse amount or type of food, it’s probably fine.
Keep in mind it’s never what we eat, but how many calories we eat, that determines weight gain or weight loss. You don’t want your body to go into starvation mode. You don’t want to have cravings either. So, if you can manage 300 cal a meal, or not really have meals and just eat 900 cal worth of stuff all day and not be hungry, more power to you.