Rapid weight loss isn't good for you and you are more likely to lose muscle tissue than fat! Going from eating regular meals to perhaps one small snack a day, alongside exercising is not good for your body as you aren't fueling it properly with what it needs. Burning more muscle than fat is not going to help you lose weight, it will actually slow your metabolism and result in you STORING fat. Don't crash diet, don't perform drastic measures to lose weight, the process is long but achievable when done correctly!
Reference - Daily Mail - http://www.dailymail.co.uk/health/article-2642236/The-reason-crash-diets-Rapid-weight-loss-leads-muscle-loss-slow-steady-slimming.html