Is 700 calories a day enough?

Short answer: No.

Long answer: While in fact each individual person requires a different amount of calories per day, the average is about 2000. 900 calories does not supply you with enough energy to undergo many basic bodily functions, and can end up with you having malnutrition and no energy throughout your day. Talk to you doctor to find out how many calories you should be eating, based on age, gender, and weight.