You can lose weight this way, but it will be much slower than if you use a steady diet for all 7 days of the week. By fasting for 2 days, you are confusing your body. For those 2 days, your body thinks that it will be without food, and it has no idea for how long. Thus, it resets its metabolism to be slower, and will process foods a lot slower the next time you eat. It takes a few days at least to re-ramp up to levels that are appropriate for what you are eating, and during that time you are likely going to gain weight. The easiest way around this is to spread out your caloric intake as much as possible (ie. eating the same calories every day, and with 4 or 5 smaller meals instead of 3 big ones). Then, by exercising you are forcing your body to use calories regardless of caloric intake. This increases your metabolism more and makes fasting unnecessary. But, don't do exercises that don't include much movement (like lifting weights, crunches, sit ups) because they only help bui...