I don’t know about too fast…I’m guessing everyone is different. But rapid weight loss can be just losing water weight – make sure you’re hydrated.
I don’t know about your details (BMR, TDEE etc) but 1100-1200 calories seems like a VERY tiny amount for a person like you. My weight is similar to yours (currently 178, but I’m 5’4″)and even at a sedentary rate, my TDEE is about 1800 calories.
In the long term, starving yourself will work against keeping the weight off. I keep reminding myself that the goal is to lose weight slowly and keep it off FOREVER.
goood luck! 🙂

I think what’s important is if you will be able to keep the weight off in the long run. You seem to be only eating 900/1000 kcal a day. That seems very little since a regular caloric restriction diet doesn’t normally go under 1200/day. I’m just wondering if you’ll be able to keep this up. I know that for me, I’d be a lot more likely to give up after a while and start eating way too much again.

Some people say you would end up in starvation mode, others believe this only happens if you undereat severely for an extensive amount of time (think hunger strikes and war prisoners). I don’t know enough about the subject to actually give an opinion on this (it’d be a wild stab in the dark) but I will say that the idea of Intermittent Fasting for most of us is finding a way of restricting our calorie intake in a way that is maintainable for the rest of our lives. I’m not sure that’s attainabe if you’re only eating 900 kcal/day.

So I don’t know if it’s too little per se, but I’m think it might resemble a crash diet rather than a way of life, which is what this ‘diet’ is designed to be.

Good luck with everything!

Ok use the TDEE calculator on this site. Read the faqs. For non-fast days, reduce your TDEE by no more than 500 but this much only if have a great deal to lose. My reduction from TDEE on non fast days is only 50. I have only about 7 more pounds/3kg to lose.

While you are doing this, and any diet, maximise your nutrition along these lines.

20g of protein each of 3 meals
5 vegetables per day at 75 grams per serve
2 fruit per day at 150g per serve
between 30-50grams of fibre per day. Preferably 50 if you can get it up there. look up foods highest in fibre – these are beans lentils chickpeas.
1 cup milk per day
1 cup unsweetened yoghurt per day
healthy fats- cold pressed extra virgin olive oil or other nut oils, nuts/seeds 30grams per day maximum, yellow cheese maximum 40g per day or white cheese i think its about half a cup. Don’t over restrict your healthy fats i.e. the oil. you can also use butter and cream but in moderation to match your calories.
minimise processed and refined foods
no more than 6tsp of sugar per day

choose vegetables over bread, limit bread. choose whole grains most of the time when you do eat. don’t fill up on pasta and rice. fill up on vegetables.

Cook your food.

Fast days: try to go without food until you start to experience hunger which may be around lunchtime. Have a good healthy meal. A good healthy meal will keep you going for the rest of the day if necessary. I have found vegetables very sustaining on a fast day but i am now also eating more protein instead of vegetables to prevent muscle wasting but i can’t eat the recommended 50g per day.

At breakfast time try to make do with a salt broth like vegemite broth, or miso, or stock cube. this will prevent headaches. Drink also plenty of water through the day. Headaches are caused by dehydration but you do need to have an adequate salt intake and when you fast you lose a lot of salt.

I also have nescafe with milk but its better if i can leave this until later in the day and skip it at breakfast time.