What Is a Very Low-Calorie Diet?

very low calorie diet

Verywell / Debbie Burkhoff 

At Verywell, we believe there is no one-size-fits-all approach to a healthy lifestyle. Successful eating plans need to be individualized and take the whole person into consideration. Prior to starting a new diet plan, consult with your healthcare provider or a registered dietitian, especially if you have an underlying health condition.

A very low-calorie diet (VLCD) is a rapid weight-loss program in which calories are severely restricted. It 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. 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.

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.

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

What Can You 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 only eat one type of food (such as the mono-diet).

What You Need to Know

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
  • Doctor prescribed meal replacements (bars, shakes, specific foods)

What Not to Eat
  • Foods other than those doctor prescribed

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).

The bars and shakes used in a VLCD are not the same as diet products 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

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

  • Nutritionally balanced

Cons
  • Side effects

  • Must be medically supervised

  • Not a long-term solution

Pros

Efficacy

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.

Cons

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.

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).

Sustainability

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.

Is a Very Low-Calorie Diet Right For You?

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.

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

Health Benefits

Body Composition

A greater rate of weight loss in a shorter period can result in better physical improvements, including fat loss, waist circumference, the relative amount of lean mass compared to body fat, nutritional status, and walking stride.

Reduced Side Effects of Some Conditions

VLCD can also improve symptoms in patients with diabetes, psoriasis, osteoarthritis, and obstructive sleep apnea.

Prepare for Surgery

VLCD can help people with obesity lose enough weight to prepare them for bariatric surgery.

Health Risks

Low Calcium

The nature of VLCD means that it can be more difficult to obtain enough nutrients. One negative result of VLCD is the potential for bone density loss due to low calcium levels.

Adverse Side Effects

VLCD can cause side effects such as headaches, weakness, fatigue, nausea and vomiting, constipation, dehydration, low blood sugar, bad breath, diarrhea, and dizziness.

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.

Hair Loss

Hair loss is a potential long-term side effect of VLCD.

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 tough 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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