900 calories diet - can i go on for it for months ?

it's not enough.

i did around 900 a day for months back in '05. i lost a lot of weight, but i also lost a lot of muscle. i ended up having to go back and do a portion of it again after the diet was over because my metabolism was a bit messed up. the second leg of my diet was slower, but it was actually healthy, and the weight has stayed off this time.

honestly, i understand the reason for picking this kind of ultra-low cal thing, because you want the the weight gone right now. there's probably nothing anyone could have said to talk me out of it at the time. however, my recommendation is to lose the weight the right way (with a proper calorie deficit and exercise), and keep it off by doing maintenance for life.

anyway, best of luck in whatever you choose.

.....You must be new here. Keep us posted on what you decide to do!

I am 250 lbs. and had 900 calories for breakfast..... If you wanna go that route by all means be my guest but if you want long term sustainable results I would suggest you eat more especially if you are going to add in exercise.... I am still in a calorie deficit to lose 1/2 lb. a week and consume 3400 calories a day.. Food is fuel it is not the enemy... Best of Luck...

How about 700? Maybe 600? Truth is, if you deprive your body of calories, it will react negatively. It is like tellin a 4 year old that he cant read a book because he colors in them. I say, increase your intake, as well as your workout. If you have nothing else going on besides work, then you can EASILY fit in about 1-2 hours of working out. It is all just a choice. If you have other obligations, then you are going to have to work that out. 30 min a day of "light" workout is not going to cut it. I work out about 10-12 hours a week, and eat over 10,000 calories easy. I am 5'8", 215. By the end of this week, I am aiming for 212. Put simply, If you work out more, and burn more calories, you can eat more. Just reduce the fat, and increase the proteins and fibers. If you eat the same amount of cake as opposed to carrots, or a salad, you will not do anything.

Too Much Sugar destroys any kind of diet. No Ifs ands or buts.

Vegetables give your body potassium, which allows your body to regulate its sodium level. Eliminate Chips, sweets, fast food, top ramen, and un-lean ground beef, along with other things. Eat lean, and stay consistent. You will do fine.

Not all sugar is equal. There is a world of difference between natural fructose and refined processed sugar. Your body is built to process fructose. Don't confuse her even more dude.

I like to direct people here to figure out how many calories they should be eating. This guy spent a lot of time laying it all out for us.

http://www.myfitnesspal.com/topics/show/654536-in-place-of-a-road-map-2-0-revised-7-2-12

my personal trainer actually had me on a 900 calorie diet, i think i lost 1.5 kg in three weeks and that was it! he also had me doing 4 workouts a week were i would have to burn 900 calories. he was shocked that i didnt lose anything more. but it was way too low and in my opinioin really unproffesional to put me on a diet with so few calories. i was really cranky, tired and really stressed! trying to only eat that much. It did teach me how to cook low calorie and nutritional meals though. Like everyone here I believe that aiming between 1100- 1200 cals a day is for the best, its an amount that you can manage to consume and sustain for a life time. 900 calories is not something you can keep up.

If you have nothing else going on besides work, then you can EASILY fit in about 1-2 hours of working out. It is all just a choice. If you have other obligations, then you are going to have to work that out. 30 min a day of "light" workout is not going to cut it.

For someone making a change from a sedentary lifestyle, 30 min x 3 would be a huge Improvement and a great start. I thnk suggesting that someone just starting out try to do 1-2 hours a day is just setting someone up for failure.

^This. Any additional movement is good. As you get smaller and more fit, you'll be able to do more -- may even want to do more. I know it's frustrating to feel like you're at your breaking point, but really, dropping to 900 is not sustainable. The risk, beyond the long term risks to your body, are that you may get so tired of the deprivation (especially if the pounds don't start melting off) that you'll say ***-it and give up completely.
Because I stated in my goals that I wanted to lose 2 lbs. a week (my start weight was 256 and I'm 5'3", so I'm pretty close to your stats), my daily goal is set for 1,200 calories. That said, I frequently end up eating 1,500 to 1,600 (and sometimes even eat at my maintenance level of 2,060, like yesterday and Monday.) Still, I have been losing 2-3 pounds most weeks. (Sometimes I exercise a bit and eat back a fair amount of the calories, and those are the higher loss weeks, but even on the lower exercise weeks, I do OK.) Twice now, I've gained a little bit (1-2 lbs.) because I ate way over and had wine and didn't get much exercise, but that corrected itself the following week or within two weeks.
It can be done. Eat healthy. Take your time and you'll see results that will last and you'll develop an eating plan you can live with long-term. You didn't gain all the weight overnight and it's not going to come off overnight either. But if you lose steadily and slowly it will stay off. I'm finally getting it this time around.

People who have had weight loss surgeries eat like this all the time.

but they are typically under the care of a doctor who specializes in the field.

Lots of people are going to tell you NO, DON'T...BUT
IF you do this WITH A DOCTOR. You're fine. When you start exercising, eat those calories back! Only a dr can tell you to go ahead with that low of a calorie limit.