I wrote the following somewhere else about the things I've been told about VLCD, hope it's helpful.
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"VLCD are not safe"
VLCD have been around since the 1920s, but in the 70's a number of deaths occurred in people using 'Liquid Protein Diets' which bear no resemblance to the VLCD of today. They were withdrawn from the market and since then there have been no cardiac problems attributed to VLCD. Millions of people have used VLCD and they have been studied extensively - there simply is no evidence at all that they are unsafe. There have been two high profile deaths in the UK where the media blamed VLCD. Tragic as it is when young people die, it happens. Young people can die whilst on Weight Watchers or any other diet and given the number of people on a diet at any time, it is bound to happen that people die whilst also being on a diet. Being markedly obese is risk factor for cardiac problems and in one of the cases, the woman in question had weighed 33 stone and at the time of her death was 23 stone. The inquests found no link between the deaths and the diet, but that doesn't sell newspapers. The most serious known side effect of VLCD is the possibility of developing gallstones.
It should be noted that ketogenic diets are safely used to treat epilepsy in children (and some adults) for indefinite periods of time, although they are burning fat that they take in from their diet rather than stored fat. There have also been groups of people throughout history, such as the Inuit, who have lived on a ketogenic diet their entire life. VLCD are clinically supervised and are endorsed, with specific criteria, by the NHS (NICE Guidelines), the US government and lots of other notable health organisations.
"VLCD cause long term health problems and mess up your metabolism"
On the contrary, VLCD cause marked improvements in blood-pressure, bad fats circulating in the blood and insulin sensitivity very early on in the diet. There is no evidence at all the VLCD cause long term health problems and most of the things that have been suggested to me that it might cause seem to be based on the kind of pseudo-science that abounds in diet literature.
"Losing weight slowly is healthier for you"
Someone told me that I should take up jogging and 'just accept that it'll take 2 years to lose the weight' as that would be 'healthier'. It makes no rational sense whatsoever to suggest that being overweight for longer is healthier for you than not to be.
"If you lose weight slowly, you'll keep it off"
It doesn't matter how you achieve weight loss, the chances of long-term success are not very good. That is a fact. The only way to keep lost weight off is to make permanent and substantial to your life afterwards. The idea that if you lose weight slowly, you'll keep it off is based on the idea that by doing that you're more likely to make those long-term changes, but that's simply not true. My mother has been on Weight Watchers for most of the last 30 years that I can remember. There is no evidence whatsoever that slower weight loss has better long outcomes than quick weight loss and in some research VLCD had the best outcomes if they were combined with CBT and taking up a proper exercise routine.
"No, what you should do is [this diet]"
Different diets work for different people for different reasons. I've chosen to do a VLCD because of the CBT aspect, because removing food completely from the equation will force me to deal with things that come up without turning to food/wine in a way that more conventional diets never do and that the relatively quick weight loss will mean that exercise is easier, more enjoyable and more efficient.