Very Low-Calorie Diets: Everything You Need to Know
Traditional low-calorie diets typically allow between 800 and 1,500 calories a day. However, an alternative 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 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. 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?
If you have a BMI over 30 (which your doctor may call “obese”), then a very low-calorie diet may allow you to lose about 3 to 5 pounds per week, for an average total weight loss of 44 pounds over 12 weeks. That amount of weight loss can improve weight-related medical conditions, including diabetes, high blood pressure, and high cholesterol. However, VLCDs are no more effective than more modest dietary restrictions in terms of long-term maintenance of reduced weight.
Once you go off the diet, you need to change your lifestyle, committing to healthy eating and regular physical activity. Behavioral therapy may help you learn how to change your unhealthy patterns and make plans that you can keep. By sticking to a long-term commitment, you can maintain your loss.
Are Very Low-Calorie Diets Safe?
VLCDs are not suitable for everyone. Talk to your doctor to see if this kind of diet is appropriate for you. If you have a body mass index (BMI) greater than 30, then very low-calorie diets are generally safe when used under proper medical supervision. Use of VLCDs in people with a BMI of 27 to 30 should be reserved for those who have weight-related medical complications.
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 4 to 16 weeks report minor side effects such as fatigue, constipation, nausea, and diarrhea. 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 are more common during rapid weight loss. It’s unclear whether VLCDs directly cause gallstones or whether the amount of weight loss is responsible for them.
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. Talk to your doctor or dietitian about making sure you get the nutrients you need while on a VLCD.