"Drastically limiting your intake of glucose, the usual energy source for your cells, reduces insulin secretions in your body. Since low levels of glucose are coming in, the body uses what is stored in the liver and then the muscles," says Rania Batayneh, MPH, the author of The One One One Diet: The Simple 1:1:1 Formula for Fast and Sustained Weight Loss. After about three or four days, all of the stored glucose is used up.