More than 100,000 people across the UK have signed up for the liquid-based LighterLife programme, which involves obese dieters consuming just 530 calories a day for three months at a time.

Professor Mike Lean, head of human nutrition at Glasgow UnADVERTISEMENT iversity, claims the scheme takes advantage of vulnerable people and can lead to health difficulties.

But the company behind the scheme, which has annual turnover of £18m, insists it helps people to lose weight quickly and safely. LighterLife, which has franchises across Scotland, has devised a programme in which people who are three or more stone overweight consume nothing but its own range of powdered soups and shakes.

A 12-week supply of "foodpacks" costs around £720.

Lean, who is also a consultant physician at Glasgow Royal Infirmary, advised people to think twice before considering commercial, very low calorie diets.

He said: "If people go on what amounts to a starvation diet – and just over 500 calories a day is close to a starvation diet – they may be liable to run out of nutrients in a relatively short period of time.

There is nothing magical about what LighterLife offer and nutritionally their programme is very boring."

He added: "You don't have to buy expensive products to lose weight and you certainly don't have to believe the hype. If people are tempted to try these schemes they should go and see their GP and find out what they can offer. Our results, in the NHS, match up to anything that the commercial organisations can offer and nobody is getting rich from it."

Lean said two meals a day of porridge, fruit and skimmed milk could be as effective as the liquid regime offered by private firms, and claimed "quick-fix" diet regimes often backfired. "It is fairly simple for people to get quite rapid weight loss in a few weeks, but the problem is that they don't know how to keep their weight down afterwards. They tend to quickly revert back to what they were doing before and it is terribly demoralising to put it all back on again.

He warned: "There will be some people for whom 12 weeks on a dramatic very low calorie diet could lead them to metabolic trouble."

He said guidelines surrounding "extreme" diets need to be tightened. "I am sure that LighterLife's counsellors are very well-meaning, but they are not professionally qualified. Why are we allowing them to do this?"

"In a responsible society it shouldn't be permitted for companies to be marketing and profiteering in this way."

The National Institute for Clinical Excellence guidelines state that very low calorie diets should only be used for a maximum of 12 weeks.

LighterLife complies with this by ordering dieters to up their calorie intake for a week after three months, and then returning to their previous regime.

The LighterLife diet has been associated with constipation, hair loss, nausea and disrupted periods. One former diet user said: "After I completed the 12-week programme my hair started falling out in clumps. I couldn't stop crying, but my counsellor told not to worry and to concentrate on the fact that I had lost lots of weight."

But LighterLife's scientific adviser Professor Iain Broom said Lean's remarks were little more than scaremongering.

The Robert Gordon University academic, who is also employed by the firm said: "A very low calorie diet of the sort used by LighterLife used under medical supervision is a safe and effective way for obese people to lose weight.

"This programme is only run with the permission of the GP.

"Patients have to fill in a personal questionnaire and if there is anything in their medical history that can lead to problems then they are excluded from the programme..

Broom said that people completing the course were given a weight management programme as well as sessions of cognitive behavioural therapy run by the firm's counsellors.

"Although a lot of the counsellors aren't medically qualified many of them are nurses and they undergo a prolonged period of training."

The firm warns about potential side effects in its literature.

Scotsman