I once knew a guy who went on a lengthy fast and after the 11th day looked like a totally different person. No idea about one-meal-a-day for a week though except that you WILL lose weight (unless of course that one meal is a FEAST).
that won't help at all what you need is to do basic work outs at least 30 sit ups and 10 push ups but eat 5 times a day but small portions of it .. that will keep your stomach not full but also not hungry.
Do not fast like this, your metabolism slows down and you burn very little fat; and when you start eating again, your body's going to say, "Whew, we almost starved. I'm going to have to be careful about burning too much energy and increase my fat reserves in case my person is threatened with starvation again." Eat small, wisely planned meals, about 5 times a day, then your body won't worry about starving and will be happy to burn the fat when necessary. Increase exercise along with the smart diet and you'll get healthy and look healthy.