top of page

Very Low Calorie Diets: When and Why?

Very low calorie diets (VLCDs) offer less than about 800 calories per day and are designed to be a brute-force method for rapid weight loss. In this article we will examine the relatively rare circumstances when a VLCD makes sense.

Very Low Calorie Diets: When and Why?

A very low-calorie diet (VLCD) is a diet that typically includes fewer than 800 calories per day, which is considerably lower than the standard caloric intake of an adult, generally ranging from 1800 to 2500 calories. These diets often involve the use of meal replacement products, such as shakes or bars, to ensure an individual receives essential nutrients while significantly reducing their caloric intake.

One of the key downsides of VLCDs, and calorie restriction diets in general, is their unlivability. For most individuals, drastically cutting calories can lead to feelings of deprivation and hunger, making the diet difficult to stick to. Moreover, the restrictive nature of such diets fails to leverage differences in food quality, with the focus instead being placed predominantly on caloric content. This can lead to inadequate intake of essential nutrients, negatively affecting overall health.

However, despite these downsides, there are several circumstances in which a VLCD may be indicated:

Pre-Surgical in Morbidly Obese:

In preparation for surgery, morbidly obese patients may need to lose weight quickly to reduce the risks associated with anesthesia and surgery.

Psychological Boost:

For individuals who are demoralized about their weight, the rapid weight loss achieved with a VLCD can provide a much-needed psychological boost.

Urgent Rapid Weight Loss:

In certain situations where rapid weight loss is necessary, such as an upcoming critical job interview or a role for an actor that requires them to lose weight quickly, a VLCD might be beneficial. In addition, athletes preparing for a weight category event or individuals preparing for a special occasion like a wedding might also consider a VLCD.

Most VLCDs often involve liquid meal replacements like Optifast, which typically demand total abstinence from other foods. This drastic shift in eating habits can lead to feelings of deprivation, fatigue, irritability, and constant hunger.

Results of a VLCD vary significantly based on individual compliance. For highly compliant patients, a weight loss of up to 3-5 pounds per week can be expected initially, slowing down to 1-2 pounds per week after the first month.

However, VLCDs do come with risks, including the development of gallstones due to rapid weight loss. Furthermore, transitioning back to regular eating after a VLCD can be challenging, with the potential risk of weight regain if not properly managed.

In the long term, it's important to understand that VLCDs are not meant to be a permanent solution. The patient should not consider the diet "over" after merely losing the weight. Instead, there is a significant transition phase back to 'normal' eating, requiring a gradual reintroduction of a variety of foods and portion sizes. The ultimate goal is to transition into a sustainable, balanced diet and a healthier lifestyle.

Moreover, it's crucial to note that any VLCD should be undertaken under medical supervision due to the potential health risks associated with such extreme calorie restriction. Regular monitoring is necessary to ensure that the individual is not developing any medical complications and is receiving the necessary nutrients.

Finally, the success of a VLCD largely hinges on the individual's commitment to maintaining a healthier lifestyle post-diet. Regular exercise, ongoing dietary changes, and in some cases, behavioral therapy, can all contribute to maintaining weight loss achieved through a VLCD.


  1. Tsai AG, Wadden TA. The evolution of very-low-calorie diets: an update and meta-analysis. Obesity (Silver Spring). 2006 Aug;14(8):1283-93. doi: 10.1038/oby.2006.146. PMID: 16988070.

  2. Johansson K, Neovius M, Hemmingsson E. Effects of anti-obesity drugs, diet, and exercise on weight loss, metabolic disease and quality of life. Drug Discov Today Dis Models. 2010 Winter;7(4):e85-e93. doi: 10.1016/j.ddmod.2010.11.002. PMID: 21383909; PMCID: PMC3047996.

  3. Strychar I. Diet in the management of weight loss. CMAJ. 2006 Jan 3;174(1):56-63. doi: 10.1503/cmaj.045037. PMID: 16389237; PMCID: PMC1319349.

Implementing a VLCD requires careful medical supervision, as it can pose health risks if not managed properly. Apart from cholelithiasis (gallstones), which is a significant risk with rapid weight loss, other potential side effects include fatigue, constipation, nausea, diarrhea, and nutrient deficiencies.

The restrictive nature of a VLCD often results in a monotone 'feel', as it requires total abstinence from other foods and replaces them with liquid meal replacements. This shift in eating habits can lead to feelings of deprivation, fatigue, irritability, and constant hunger. For some individuals, the diet can feel repetitive and unsatisfying, causing distress and potentially leading to non-compliance.

When transitioning from a VLCD back to 'normal' eating, it's crucial to reintroduce food groups gradually to allow the body time to adjust and to prevent rapid weight regain. It can be a challenging process, often requiring the support of a dietitian or nutritionist. It's crucial to establish a balanced and sustainable eating pattern during this transition phase.

In the long term, a VLCD is not a sustainable weight management strategy. Weight maintenance post-VLCD requires a balanced, nutritious diet coupled with regular physical activity. The transition from the VLCD should be seen as the beginning of a new phase in the individual's weight loss journey, rather than the end of the diet. Learning new eating behaviors, portion control, and coping mechanisms for stress and emotional eating can all contribute to successful long-term weight management post-VLCD.

Lastly, it's important to remember that weight loss and maintenance are deeply personal and vary significantly between individuals. While a VLCD can provide a rapid weight loss 'jump start' in certain circumstances, its success largely depends on the individual's motivation, readiness for change, and long-term commitment to a healthier lifestyle.

  1. Wing RR, Phelan S. Long-term weight loss maintenance. Am J Clin Nutr. 2005 Jul;82(1 Suppl):222S-225S. doi: 10.1093/ajcn/82.1.222S. PMID: 16002825.

  2. Wadden TA, Butryn ML, Wilson C. Lifestyle modification for the management of obesity. Gastroenterology. 2007 May;132(6):2226-38. doi: 10.1053/j.gastro.2007.03.051. PMID: 17498514.


bottom of page