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.

What Is a Very Low-Calorie Diet?

A very low-calorie diet (VLCD) is a rapid weight-loss program in which calories are severely restricted, often to 800 calories or fewer. A calorie level this low may be considered semistarvation or a crash diet. This diet is dangerous unless you are under medical supervision for reasons that necessitate weight loss, such as surgery. 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 obesity.

Body Mass Index (BMI) is a dated, biased measure that doesn’t account for several factors, such as body composition, ethnicity, race, gender, and age. 


Despite being a flawed measure, BMI is widely used today in the medical community because it is an inexpensive and quick method for analyzing potential health status and outcomes.

These diets 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.

For example, 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. These 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 a very low-calorie diet is appropriate for you. The VLCD is not a long-term solution as it is too low in energy and nutrition.

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 You Can Eat

In most cases, people following a VLCD consume liquid protein shakes or meal-replacement bars in place of food for a designated 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 limit intake to one type of food (a type of mono-diet).

What You Cannot Eat

The VLCD is mostly based on limiting calories and for this reason, it is unlikely that you will eat any foods that are calorie-dense. For very-low-calorie diets that rely on meal replacements only, you will not eat anything other than those products.

How to Prepare a Very Low-Calorie Diet & Tips

Your doctor-prescribed VLCD 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).

You may be required to purchase meal replacement products if that is part of your prescribed diet. The bars and shakes used in a VLCD are not the same as diet products at the grocery store. Instead, meal replacements are specially formulated to contain adequate vitamins and nutrients, so patients' nutritional requirements are met.

Pros of a Very Low-Calorie Diet

A VLCD can be a good choice for specific people and situations. It is almost always prescribed for medical reasons, to help manage obesity and conditions related to it.

  • 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.
  • Improved body composition: A greater rate of weight loss in a shorter period can result in 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: Following a VLCD can improve symptoms in patients with diabetes, psoriasis, osteoarthritis, and obstructive sleep apnea. Obesity may cause symptoms and side effects with these conditions, so weight loss helps alleviate them.
  • Preparation for surgery: In some cases, preliminary weight loss is important prior to bariatric surgery. A VLCD can help people with obesity lose weight to prepare for surgery.

Cons of a Very Low-Calorie Diet

Because of the severe calorie restriction in a VLCD, there are some health risks. Health care practitioners will weigh these against the potential benefits of the diet.

  • Side effects: Many patients who follow a very low-calorie diet for four to 16 weeks experience side effects such as headaches, weakness, fatigue, nausea and vomiting, constipation, dehydration, low blood sugar, bad breath, diarrhea, and dizziness. These symptoms usually improve within a few weeks. Hair loss is a potential long-term side effect of VLCD.
  • 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.
  • Lack of nutrients: 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.
  • 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.

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 intake severely, down to 800 calories or less, which is why it must be overseen by a doctor.

A very low-calorie diet should only be followed if prescribed to you by your doctor. Your doctor will let you know if the benefits of a very low-calorie diet outweigh the potential risks in your specific case. Do not attempt a very low-calorie diet without discussing it with your doctor and committing to expert supervision.

A Word From Verywell

Many people 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 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 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.

Remember, this or any diet may not be necessary for you and many diets out there simply don’t work, especially long-term. While we do not endorse fad diet trends or unsustainable weight loss methods, we present the facts so you can make an informed decision that works best for your nutritional needs, genetic blueprint, budget, and goals.

If your goal is weight loss, remember that losing weight isn’t necessarily the same as being your healthiest self, and there are many other ways to pursue health. Exercise, sleep, and other lifestyle factors also play a major role in your overall health. The best diet is always the one that is balanced and fits your lifestyle.

8 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  6. Muscogiuri G, Barrea L, Laudisio D, et al. The management of very low-calorie ketogenic diet in obesity outpatient clinic: a practical guide. J Transl Med. 2019;17(1). doi:10.1186/s12967-019-2104-z.

  7. Johansson K, Sundström J, Marcus C, Hemmingsson E, Neovius M. Risk of symptomatic gallstones and cholecystectomy after a very-low-calorie diet or low-calorie diet in a commercial weight loss program: 1-year matched cohort study. Int J Obes (Lond). 2014;38(2):279-84. doi:10.1038/ijo.2013.83

  8. U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2020 – 2025 Dietary Guidelines for Americans. 9th Edition. December 2020.

By Rachel MacPherson, BA, CPT
Rachel MacPherson is a health writer, certified personal trainer, and exercise nutrition coach based in Montreal.