Traditional low-calorie diets typically allow between 800-1,500 calories a day. If you have a BMI over 30 (considered “obese”), then a very low-calorie diet may allow you to lose about 3 to 5 pounds a week. In the long term, very low-calorie diets aren’t any more effective than modest diets – the key to maintaining weight loss is changing your lifestyle and committing to healthy eating and regular physical activity.
For people who are overweight but not obese (those with BMIs between 27-30), very low-calorie diets should be reserved for those with weight-related medical problems. Pregnant or breastfeeding women, children, teens, and people over 50 are generally not recommended to eat very low-calorie diets except in specialized treatment programs.
"Very Low-Calorie Diets: Are They Safe for Weight Loss?" WebMD. WebMD, n.d. Web. 30 June 2014.