Pretty fast actually. Just so you know it depends a little on your weight. Your body needs about 2000 calories a day (depending on weight and hight), a pound of fat = 3500 calories, so in order to lose a pound a week you must eat less then 1250, or more with exercise. You will be losing about a pound in a half a week, which is actually amazing, because the slower you lose weight, the slower you put it back on. Remember to drink lots of water and take a multivitmen, as you are probably not getting all of the daily reccommended nutrients! good luck! (just so you know, i am not a doctor, i do not know this for a fact, i know what i have researched personally when i lost 40 pounds.) BEST OF LUCK!