I'm a little late to this thread, but the 600 cal/day two day a week is what I've been doing for the past month on the 5/2 fast diet and it has been a godsend. The fat is disappearing around my neck and my gut and I've lost 8 pounds in about 6 weeks. I workout, eat healthy, etc. The fasting is the key though, as it gets your liver to function in a different mode as it has evolved to do, and which it never does as we are constantly eating in our society. I do this on trips as well. I actually feel more alert without eating and the video explains increased brain function as well. The first couple of times you do it takes some motivation as it is something new. After that it is easy. It is kind of like getting your second wind while running, you will need to get over the hump during the day then you'll be fine. Watch this video that was first on PBS for why this works.
Eat, Fast and Live Longer - Horizon on Vimeo