What is a Very Low Calorie Diet?

Can You Lose Weight on 900 Calories a Day?

Protein cocktail in a glass and a scoop on a white wooden table
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A very low-calorie diet (VLCD) is a rapid weight loss program where calories are severely restricted. Because food intake is so limited, VLCDs should only be followed under a doctor's supervision. The diets are often used to help obese patients achieve significant, short-term weight loss as part of a comprehensive weight loss program.

How They Work

VLCDs are designed to produce rapid weight loss at the beginning of a weight loss program. In most cases, liquid shakes or meal replacement bars replace food for a period of time ranging from several weeks to several months.

Patients on a very low-calorie diet usually consume about 800 calories a day. Some dieters try to lose weight on 900 calories a day. The meal replacements are specially formulated to contain adequate vitamins and nutrients so patients' nutritional requirements are met. The bars and shakes used in VLCDs are not the same as diet bars and shakes that you can purchase in the grocery store. Some VLC diets include lean proteins, such as fish and chicken.

Who Should Follow a VLCD?

Very low-calorie diets are intended for patients whose body mass index (BMI) is greater than 30 with significant complications such as diabetes or high blood pressure. VLC diets are not normally used for patients with a BMI between 27 and 30 unless they have medical conditions related to their weight.

VLC 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.

A physician should decide on a case-by-case basis whether or not a VLC diet is appropriate for a patient.

Quick Weight Loss on 900 Calories a Day or Less

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 not healthy and not sustainable. 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 fad diets or trendy weight loss programs that provide only 900 calories a day or less. You'll see many plans advertised in magazine and online, some with healthy claims attached to them. But without proper nutrition, you are likely to get tired and may have other health problems as well.

If you are obese and trying to manage medical conditions that are aggravated by your weight, your doctor can help you decide if a very low-calorie diet is right for you.

An obese patient can lose about three to five pounds per week while following a VLC 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 to 25 percent of their initial weight if they start with very low-calorie diet and transition to a healthy lifestyle, a calorie-controlled eating plan, and exercise program.

Side Effects

Many patients who follow a VLC 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.

Long-Term Results

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 weight regain. VLC participants typically maintain a five percent weight loss after four years if they adopt a healthy eating and exercise plan.

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Article Sources
  • National Institutes of Health/National Institute of Diabetes and Digestive and Kidney Diseases. Weight-control Information Network. WIN - Publication - Very-Low-Calorie-Diets. 29 Nov 2007.