Many very low-calorie diets are commercially-made formulas of 800 calories or fewer that replace all the food you usually eat. Others, such as the well-known grapefruit diet (also called the Hollywood Diet), rely on eating a lot of the same low-calorie food or foods.
Very low-calorie diets are not the same as over-the-counter meal replacements, which you substitute for one or two meals a day.
How Effective Are Very Low-Calorie Diets?
Losing that amount of weight may improve weight-related medical conditions, including diabetes, high blood pressure, and high cholesterol. But in the long-run, very low-calorie diets aren't more effective than more modest diets. Once you go off a diet, you need to change your lifestyle, committing to healthy eating and regular physical activity.
Are Very Low-Calorie Diets Safe?
Very low-calorie diets are not OK for everyone. Talk to your doctor to see if this kind of diet is appropriate for you.
If your BMI is greater than 30, then very low-calorie diets are generally safe when used under proper medical supervision. For people who are overweight but not obese (BMI of 27-30), very low-calorie diets should be reserved for those who have weight-related medical problems and are under medical supervision.
Very low-calorie-diets are not recommended for pregnant or breastfeeding women, and are not appropriate for children or teens except in specialized treatment programs. They also may not be OK for people over age 50, either, depending on the potential need for medications for pre-existing conditions, as well as the possibility of side effects.