Review: Very Low Calorie Diets For Weight Loss
The term “very low calorie diet” (VLCD) refers to diets that provide <800 kcal a day with high levels of protein and minimal carbohydrate to encourage weight loss with minimal loss of lean tissue and supplemented with vitamins, minerals, electrolytes and fatty acids to ensure adequate nutrition.
Such diets are almost impossible to concoct using regular foods, which is why they are generally offered as a liquid “formula” diet.
Although such diets have been used for almost 100 years, they are are not usually recommended for routine weight management because of potential medical complications. When used they should always be medically supervised by health professionals familiar with their use.
While medically supervised VLCDs are often the safest way to rapidly induce a substantial weight loss where needed (e.g. in a patient with severe obesity needing to lose large amounts of weight for an urgent surgical or diagnostic procedure), these diets continue to be used as a more general approach to weight management.
Now, Parretti and colleagues, in a paper published in Obesity Reviews, provide a systematic review and meta-analysis of the clinical effectiveness of VLEDs in randomised controlled trials.
Their analysis included 8 papers, which describe 12 randomized controlled trials comprising 14 VLCD intervention arms and 12 control arms of at least 12 month duration.
The 12 trials randomized 522 adult participants to VLCD and 452 adult participants to a comparator programme. The majority of participants were women (median 71%) and median baseline BMI 38.2 kgm2.
The median duration of the VLCD intervention was 10 weeks after which patients received varying amounts of further support.
Overall, the difference in weight loss between the VLCD and control arms at 12 months was about 4 Kg, a difference that shrank to less than 1.5 Kg at 24 and 38-60 months.
Discontinuation rates overall approached 20% in both VLCD and control arms. The only major complication reported was one case of cholecystitis leading to a cholecystectomy in the VLCD arm.
There was also a significantly higher incidence of transient hair loss in the VLCD group (49 vs. 8%).
The majority of the events reported were transient effects such as tiredness, dizziness and cold intolerance.
From their analysis the authors conclude that,
“…this review provides strong evidence that current prohibitions on use [of VLCDs] are unnecessary and provide reassurance that routine use in specialist obesity clinics should be considered when behavioural treatments alone have not produced sufficient weight loss.”
“However, the trials reviewed provide no evidence to suggest that providing a VLCD without behavioural support is effective compared with behavioural support but suggest that adding a VLED to a behavioural programme is effective.”
Be that as it may, one must also consider the cost-effectiveness of the intervention (not mentioned in the paper).
After all (as mentioned in the paper), the use of VLCDs is best left to specialists and their use does require significant additional monitoring (including routine lab work, ECG, etc.) to ensure safety (as was provided in most of these studies).
Thus, whether or not an additional couple of kilos truly warrant the extra cost of specialist care and monitoring remains to be shown.
My conclusion from this study is that while VLCDs are certainly safe when supervised by obesity specialists, their routine use for weight management in the long-term may not be all that superior to a behavioural intervention alone.
Nevertheless, VLCDs can provide benefits for selected patients especially when rapid weight loss is indicated.