Hi KronicSonic! With a BMI of 40.04, I am still technically morbidly obese. I have lost 3.94KG on this diet since Jan 8 and I fully expect to no longer be MO with my next weigh in.
Now I'm going to say things that others might disagree with, but here goes. I think with your weight, perhaps 600 calories is unreasonably low. Have you actually calculated your Total Daily Energy Expenditure? Perhaps your fasting calorie allowance should be a bit higher until you lose some of your weight? And you know what? it's not the end of the world if you go over what you're supposed to eat. If you are really only supposed to eat 600 calories, but you eat 800 on a fast day, it's still a huge improvement over what you would have otherwise eaten? Right?
Give it another go, and try not to put so much pressure on yourself. I personally find that it's much easier to simply not eat until 6pm. I have black coffee, water and herbal tea, then in the late afternoon I usually have a cup of bouillon. If I'm feeling weak, I might have two or three, although lately I haven't been needing so much. The first few weeks I did drink more. Then I have my dinner at 6pm. Usually, this is enough for me. But if I get really hungry after dinner, I will have a healthy snack, like an apple, even though I might have already used up my calories. I try to make sure it's really healthy, and not a huge amount of calories. I might get a bowl full of baby spinach leaves and add a couple of teaspoons of dressing, or have an orange. As long as it's a health snack of fruit or veg, I do not beat myself up for it. Then, my trick for going to bed hungry is to figure out what I'm eating in the morning. Sometimes I take croissants out of the freezer to proof overnight as my morning reward for being good. It really helps!
Do you cook? Perhaps next time you could make a big pot of a low calorie soup, and simply gorge yourself on it your next fast night. You can make a cabbage soup that is satisfying and filling, and eat 10 bowls of it for 500 calories.
Thing is, even if you blow it, try not to be too hard on yourself. Yes, there are days I have gone over my 500 calories. I get it. It's hard!! But pick yourself up, dust yourself off and recognize that it's still better than what I would have done if I weren't attempting the diet