When does weight loss start to become noticeable on a 500 calorie/day diet?

Danger! cals too low: A 500 calorie/day diet can be very dangerous and should only be done under close supervision with a doctor, nutritionist and weight-loss team. Risks include: (1) not losing weight, because your body goes into "starvation mode" and slows metabolism, (2) severe malnutrition if you're not getting the right combination of vitamins, minerals, nutrients, (3) severe worsening of other medical problems.