It's a technique used in bodybuilding to force your body to use fat stores for energy rather than your daily carbohydrate intake.
Here's a link to a plan like what I am using...
http://www.muscleandfitness.com/6_weeks_lean/nutrition/54
This is an old article, but the technique is the same.
Rather than dropping carbs by 1/2, I cut them by about 90%. Don't go over the 4 day period without reintroducing some carbs. Your body will change the way it stores unused calories and fat use will be minimized. By dropping carbs dramatically, I don't have to watch calories as much. They dropped due to the selection of foods with little or no carbs.
Lose the sugar. Do not eat or drink sweets. Include soft drinks in your carb calculations.
Lose the starches. No taters, rice, bread or noodles. (for the 4 low carb days)
Switch to fat free milk.
Include a water based protein drink (from powder) several times a day to keep your body from using muscle for energy. (not pre bottled slimfast or muscle milk)
After 4 days reintroduce some carbs, but not simple sugars. Add a potato and breads. You can do this for a couple days, then start your 4 day low carb cycle again.
Repeat.