Yea you would lose weight. But its not healthy. Your body will feel like its starving itself and you eventually will feel hungry enough and go splurge somewhere and gain the weight back. However. A 700 calorie diet isnt so bad I think. Sometimes I do it on accident. I log whatever I eat in a food journal. And I am a nurse. I work three days a week twelve hour shifts. Sometimes on those days I dont eat any more then 600-700 calories. Its not on purpose. And then I go to the gym and work out. Thing is I am sincerely not hungry. I drink so much water that my body has learned to distiguish what true hunger is. And the things I eat tend to be low calorie anyways. But its not like I do that low amount of calories everyday. My normal intake is 1200 or less. But i honestly hardly ever make it past a thousand. Its not purposeful, I just dont eat that much. So it can be unhealthy, but I have been in the gym 6 days a week and do cardio and weight lifting. I prolly lost water weight in the beginning, but I have lost body fat and have slimmed down. I really dont recommend you do that low amount of calories.