What Is a Very Low-Calorie Diet?

very low calorie diet

Verywell / Debbie Burkhoff 

A very low-calorie diet (VLCD) is a rapid weight-loss program in which calories are severely restricted. VLCDs are often used to help obese patients achieve significant, short-term weight loss as part of a comprehensive weight-loss program. Because food intake is so limited and calories are restricted to about 800 a day, very low-calorie diets should only be followed in certain cases and must be supervised by a doctor.

What Experts Say

"A very low-calorie diet is a medically supervised plan eliciting rapid weight loss in those with a high BMI. Because patients eat 800 calories or less per day, it should only be done under a doctor’s supervision and paired with specialty foods to prevent nutrient deficiencies."
Chrissy Carroll, RD, MPH


The very low-calorie diet was developed in the 1970s for patients whose body mass index (BMI) is 30 or higher—people who need to lose weight quickly because of the health consequences of their obesity. VLC diets are not normally used for patients with a BMI between 27 and 30 unless they have medical conditions related to their weight, such as diabetes or high blood pressure.

Very low-calorie diets are not usually prescribed for children or teens. They are also not usually considered appropriate for older people due to potential side effects, pre-existing medical conditions, and/or medication needs. Your physician will decide whether or not a very low-calorie diet is appropriate for you.

How It Works

Very low-calorie diets are designed to produce rapid weight loss at the beginning of a weight-loss program. An obese patient can expect to lose about 3 to 5 pounds per week while following a very low-calorie diet. The average weight loss for a 12-week VLCD is about 44 pounds. This amount of weight loss can significantly improve obesity-related medical conditions, such as diabetes, high blood pressure, and high cholesterol.

Within three to six months, a patient may be able to lose about 15 percent to 25 percent of their initial weight if they start with a very low-calorie diet and transition to a healthy lifestyle, a calorie-controlled eating plan, and an exercise program.

Research has shown the long-term results of VLC diets vary significantly. Weight regain is common. Combining a VLC diet with behavior therapy, exercise, and follow-up treatment may prevent this. VLC participants typically maintain a 5-percent weight loss after two years if they adopt a healthy eating and exercise plan.

What to Eat

In most cases, liquid protein shakes or meal-replacement bars are taken in place of food for a period of time ranging from several weeks to several months. However, some very low-calorie diet plans include lean proteins, such as fish and chicken or focus on only eat on type of food (such as the mono diet).

Recommended Timing

Your doctor-prescribed very low-calorie diet may come with suggestions for when during the day to consume your meal replacements, and when to consume any food you might be eating outside of the replacement items (if any; often, you do not consume anything other than the prescribed foods).

Resources and Tips

The bars and shakes used in a VLCD are not the same as diet products available at the grocery store. Rather, meal replacements are specially formulated to contain adequate vitamins and nutrients so patients' nutritional requirements are met.

Pros and Cons

  • May succeed (short-term) where other diet plans have failed

  • Nutritionally balanced

  • Side effects

  • Must be medically supervised

  • Not a long-term solution



Doctors often prescribe very low-calorie diets when other eating plans and weight-loss attempts have failed. Studies show that these diets often work well, at least in the short term. But they need to be followed carefully and have a behavior component that teaches patients how to change their eating habits for the long term.

General Nutrition

Because the meal replacements in very low-calorie diets are specially prepared for this purpose, they help patients get the essential nutrients they are not otherwise getting from food. This is why medical supervision is essential to the safety of a VLCD.

These positives do not necessarily mean a very low-calorie diet is right for everyone. It can be a good choice for specific people and situations.


Side Effects

Many patients who follow a very low-calorie diet for four to 16 weeks experience side effects such as fatigue, constipation, nausea, or diarrhea. These symptoms usually improve within a few weeks and rarely prevent patients from completing the program.

The most common, serious side effect of a very low-calorie diet is gallstones. Gallstones often develop in people who are obese, especially in women. They are even more common during rapid weight loss. Your healthcare provider may be able to prescribe medication to prevent gallstone formation during rapid weight loss.

Medical Supervision

To safely follow a very low-calorie diet, you must have a prescription and be monitored by a physician, which will require time and money. Typically, health insurance does not cover the cost of the meal replacements (of course, you will not be buying any groceries or restaurant meals during the VLCD).


A very low-calorie diet is a short-term solution for weight loss. It is meant to be followed for a limited time. After that, patients will need to transition to a maintenance plan that includes healthy eating, exercise, and other lifestyle changes.

How It Compares

Very low-calorie diets are unique in that they are medically supervised and they eliminate all foods except for specially formulated meal replacements. Some other diets take aspects of the VLCD and modify it for more general use.

USDA Recommendations

The USDA recommends a diet of about 2000 calories (this can vary based on age, sex, weight, and activity level) for weight maintenance, and 100 to 500 fewer calories for weight loss. The VLCD reduces this severely, down to 800 calories or less, which is why it must be overseen by a doctor.

Similar Diets

Some dieters who are not obese or who are slightly overweight may try to lose weight by eating 800 or 900 calories a day. While the plan may work in the short term, it is not likely to work over the long term. These diets are neither healthy, nor sustainable.

Very Low-Calorie Diet

  • Types of Food: On this diet, patients consume prescribed meal replacements only.
  • Safety: This diet is safe if used with a doctor's supervision so that nutrition and side effects can be monitored and managed.
  • Effectiveness: VCLDs can work for quick weight loss in obese patients.
  • Sustainability: These diets are designed to be a short-term solution, to reduce body weight enough for patients to reap some health benefits. Maintenance can be difficult.

Low-Calorie Diet

  • Types of Food: A low-calorie diet can mean any eating plan that offers a reduction in calories, usually between 1000 and 1500 per day.
  • Safety: Ideally, you would see a doctor or nutritionists before undertaking this diet as well, so you can get advice on how it will work for your body and how to make sure you are not missing out on important food groups and nutrients.
  • Effectiveness: Some research shows that low-calorie diets may be more effective than VLCDs, especially when comparing short-term and long-term weight loss.
  • Sustainability: It is easier and more realistic to maintain a 1500-calorie-a-day diet than an 800-calorie-a-day one over the long term. However, a low-calorie diet requires a lot more proactive planning and food preparation than a meal-replacement VLCD.

Intermittent Fasting

  • Types of Food: One way to restrict calories is to not eat during certain hours or days. Usually on these plans, you eat a "normal" diet for several days a week, but cut back to one-quarter of your usual calorie intake on the remaining days.
  • Safety: Since the fasting is intermittent, this diet is safe for most people—but not children, teens, women who are pregnant or breastfeeding, or anyone with a history of disordered eating. It may also not be safe for people with diabetes or heart disease.
  • Effectiveness: Some research shows that this eating plan works, although it is not clear how long the benefits last.
  • Sustainability: Because the calorie restriction is limited to two or three days a week, this type of diet might be easier to stick with for a longer term.

Medi-Weightloss Diet

  • Types of Food: The Medi-Weightloss plan can sound similar to a very low-calorie diet because it incorporates medical supervision and significant calorie reduction. Some supplements and packaged foods are available, but the Medi-Weightloss plan mostly relies on foods you prepare yourself, with an emphasis (especially in the early stages) on protein, vegetables, and fruits.
  • Safety: Although this diet offers medical supervision, at least in its first phase ("acute weight loss"), it restricts calories dramatically and eliminates some food groups. It may also lead to a too-rapid loss of weight.
  • Effectiveness: There are no independent scientific studies to demonstrate how well this plan works.
  • Sustainability: The Medi-Weightloss plan has a "wellness" phase that helps clients maintain their weight loss through a recommended eating plan and weekly check-ins.

A Word From Verywell

Many dieters who go on very low-calorie diets rebound and binge eat when they get too hungry. It is possible to regain any weight you lose and even put on extra weight as a result. For these reasons, it's generally not a good idea to follow diets or weight-loss programs that provide only 900 calories a day or less. You'll see many plans advertised in magazines and online, some with healthy claims attached to them. But without proper nutrition, you are likely to get tired and develop or exacerbate health problems.

A doctor-supervised very low-calorie diet can offer that nutrition, at least, although it is likely to be very hard work to stick with. Still, in certain cases, a doctor may recommend a VLCD as the best way to lose weight in the short term. It will need to be followed up with behavioral changes and a healthy lifestyle.

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Article Sources
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