Obesity, Weight Loss, and Very Low-Calorie Diets (VLCDs)
Traditional weight loss methods include low-calorie diets that allow between 800 to 1,500 calories a day and encourage regular exercise. However, an alternative method that moderately to severely obese people may consider for significant, short-term weight loss is the very low-calorie diet (VLCD).
Many VLCDs are commercially prepared formulas of 800 calories or less that replace all usual food eaten. 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. VLCDs are not the same as over-the-counter meal replacements, which are substituted for one or two meals a day.
How Effective Are Very Low-Calorie Diets?
A very low-calorie diet may allow a severely to moderately obese person to lose about 3 to 5 pounds per week, for an average total weight loss of 44 pounds over 12 weeks. Such a weight loss can improve obesity-related medical conditions, including diabetes, high blood pressure, and high cholesterol. However, VLCDs are no more effective than more modest dietary restrictions in the long-term maintenance of reduced weight. Combining a VLCD with behavioral therapy and exercise may increase weight loss and help keep it off for the long term. Behavioral therapy helps you to recognize what causes you to overeat so that you can consciously change those behaviors.
Are Very Low-Calorie Diets Safe?
Very low-calorie diets are generally safe when used under proper medical supervision in people with a body mass index (BMI) greater than 30. Use of VLCDs in people with a BMI of 27 to 30 should be reserved for those who have medical complications resulting from their obesity.
VLCDs are not suitable for everyone. Doctors generally recommend them on a case-by-case basis and your doctor will decide whether or not such a diet is appropriate for you. VLCDs are not recommended for pregnant or breastfeeding women, and are not appropriate for children or adolescents except in specialized treatment programs. Due to the potential need for other medications for pre-existing conditions, as well as the possibility of side effects, these types of diets may not be suitable for people over 50, either.
What Are the Side Effects of Very Low-Calorie Diets?
People on a very low-calorie diet for four to 16 weeks report minor side effects such as fatigue, constipation, nausea, and diarrhea, but these conditions usually improve within a few weeks and rarely prevent people from completing the program.
The most common serious side effect seen with VLCDs is gallstone formation. Gallstones, which frequently develop in obese people (especially women), are even more common during rapid weight loss. The reason for this may be that rapid weight loss appears to decrease the gallbladder's ability to contract bile. But, it is unclear whether VLCDs directly cause gallstones or whether the amount of weight loss is responsible for the formation of gallstones.
What Are the Other Drawbacks of Very Low-Calorie Diets?
To be healthy, we need a balance of foods from different food groups. It's quite difficult to get good nutrition in as few as 800 calories (even a dietitian would have trouble doing this), especially if one eats the same foods every day.
Also, once you go off the diet, you will likely regain your weight unless you change your lifestyle and commit to healthy eating, regular physical activity, and a new outlook on food. By sticking to a long-term commitment, you can prevent your weight from increasing.