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The Facts on Very Low Calorie Diets

What are Very Low Calorie Diets?                        

Very low calorie diets or VLCDs (also known as very low energy diets or VLEDs) are artifical formulas, usually in liquid form, that completely replace all the food you usually eat. They provide 800 calories or less per day and contain protein, carbohydrate, essential fatty acids and the recommended daily allowance for vitamins, minerals and electrolytes. VLCDs are not the same as 'meal replacements' which are portion-controlled products (often liquid shakes or bars), designed to replace one to two meals per day with a low calorie meal and snack(s).

How do VLCDs work?

VLCDs provide a limited amount of energy (calories) for the body to use each day. This isn't enough to meet the energy needs of the body, so the body starts to break down its own fat stores and muscle tissue to produce energy, resulting in weight loss. On a VLCD, about three quarters of the weight you lose is body fat and one quarter is muscle, once a minimum of 50g of protein is consumed each day.

How do VLCDs help people to manage their weight?

  • VLCDs are not the first treatment plan for weight loss. Diet and lifestyle changes such as reducing portion sizes, eating fewer high calorie foods, and increasing activity levels should always be tried first. See our factsheets for more information.
  • If other weight loss methods have been unsuccessful, VLCDs may be considered when the body mass index (BMI) is greater than 30kg/m2. If your BMI is between 27-30kg/m2 (that is you are overweight but not obese), VLCDs may be sometimes considered if you have medical conditions linked to your weight which, under medical supervision, would benefit from rapid weight loss (e.g. severe obstructive sleep apnoea or prior to planned surgery).  VLCDs should only be used under careful medical supervision, so you must be medically assessed before starting a VLCD. You will need to be monitored closely and may require medication prescriptions regimens to be changed.
  • VLCDs are recommended for a maximum of 12-16 weeks only, there is very little published research on their use as a sole source of nutrition for longer than this. 
  • The National Institute for Clinical Excellence (NICE) also recommends that VLCDs may be used in the short term alongside a low calorie diet (for example 2-4 days per week) in obese people who have reached a weight loss plateau.  If VLCDs are to be used for extended periods, you will need to be linked with a specialist care centre.
  • A re-feeding period, when food is re-introduced slowly, is recommended when you have completed the VLCD. This information is provided by a registered dietitian. This time period helps to prevent changes in fluid and electrolyte balance in your body and prevents stomach pain and cramping. It also helps in adjusting eating behaviour to your new lower body weight. It may also help reduce the rate of weight regain. This time period usually lasts above 3 to 8 weeks.  Continuing to work with a dietitian or other health care professional may help you to slowly change your healthy eating habits and healthy lifestyle choice that you can keep.

How much weight can be lost on a VLCD?

On average, strict use of a VLCD results in 1.0-2.5kg weight loss (2 – 5.5lb per week), which can be very motivating. VLCDs give rapid weight loss at the start but are no better in the long-term (after 1 year) than less restrictive, low calorie diets. That is why it is so important to follow-up a VLCD with a longer term healthy eating and physical activity plan.

What's the best way to maintain weight loss following use of a VLCD?

Studies show a lot of variation in the amount of weight loss that is regained once you have completed the VLCD but, as with all weight loss plans, weight can be regained if lifestyle changes are not kept.

An active follow-up weight maintenance programme, that includes behavioural therapy, nutritional education, exercise and weight loss medications (delivered in a group setting by a team of healthcare professionals) has been shown to improve weight maintenance after a VLCD. 

Are VLCDs safe?

VLCDs are safe and effective when used in the right individuals under careful medical supervision, along side behaviour changes, nutrition education and an exercise programme. 

Who should not use VLCDs?

VLCDs should only be used under medical supervision and your doctor can advise you as to whether a VLCD is suitable for you or not.

VLCDs are not advised in certain population groups and medical conditions. These include:

  • Infants, children and adolescents
  • Adults over the age of 65 years. Caution is also advised in adults over 50 years as VLCDs are not well studied in this age group where loss of muscle mass may already be present
  • Pregnant or breastfeeding women
  • In severe diseases (e.g. systemic infections, malignancy, unstable cardiac or cerebrovascular disease, severe renal or hepatic failure, porphyria)
  • Acute psychiatric disorders
  • Type 1 diabetes mellitus

What kinds of side effects are possible with VLCDs?

  • A healthy diet includes a balanced intake of foods from different food groups. It can be difficult to achieve this and feel full on a VLCD when you are consuming a maximum of 800 calories per day. This means you may not have the energy you need for daily living and physical activity.
  • Some people on VLCDs report minor side effects such as: tiredness, dry mouth, bad breath, dry skin, headaches, dizziness, or intolerance to cold weather,
  • Some people may experience hair loss/thinning, constipation or diarrhoea (due to the low fibre content of many VLCDs), irregular periods in women, brittle nails and oedema.
  • More severe side effects include gout and gallstones. Gallstones can occur during rapid weight loss.
  • Your dietitian can help you include the nutrients you need while on this restrictive diet.

Conclusion

There is no magic answer for sustained weight loss. VLCDs may be useful to 'kick start' weight loss when used correctly that is in carefully selected clients under medical supervision. The use of VLCDs should be supported by trained health care professionals who encourage clients through the re-feeding period and beyond, and who teach them about the life-long behaviour and dietary changes needed to keep off the weight lost. Obesity is a long-term condition that needs a lifetime of attention even after a formal weight loss programme ends. The only way to manage weight in the longer term is to commit to permanent changes of healthier eating, regular physical activity and develop a positive and respectful relationship with food.

Created by members of the weight management interest group, August 2013, updated May 2016

Review date: May 2019.

© 2016 Irish Nutrition and Dietetics Institute, INDI. All rights reserved. May be reproduced in its entirety provided the source is acknowledged. This information is not meant to replace advice from your medical doctor or individual counselling with a dietitian. It is intended for educational and informational purposes only.

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