People who go on extreme diets could be seriously damaging their health, experts have warned.
Doctors advise people to eat a balanced diet
They are particularly concerned with diets that encourage people to cut out whole food groups.
Many popular diets involve reducing the intake of or cutting out completely food groups like carbohydrates.
But experts believe people who go on these diets could be storing up problems for the future.
They have called for more research into the long-term effects of some of today's most popular diets.
They also urged the government to do more to encourage people to eat healthily.
Speaking to journalists in London, Dr Susan Jebb, from the Medical Research Council's Human Nutrition Research Centre in Cambridge, singled out the Atkins diet for criticism.
She said it would be "negligent" to recommend the diet to anyone overweight and said many of its claims were based on "pseudo science".
She added: "We simply do not know the long-term health implications, and it's such a profound change from what we're doing at the moment.
"I certainly think we should be adopting a precautionary principle in terms of public health."
Dr Jebb's warning comes two months after two teams of American scientists declared that the Atkins diet was effective and safe.
The two studies, published in the New England Journal of Medicine, found that the diet resulted in more weight loss than conventional low-fat diets.
But Dr Jebb said these studies and others focusing on the Atkins diet were too small, short and limited to provide any meaningful evidence.
Lyndel Costain, a dietician, said people should not do the Atkin's diet or similar diets over the long term.
"The problems with that sort of diet is that it may be low in fibre.
"You might also restrict very important vitamins and minerals that you get in fruit and vegetables and wholegrains.
"In the short-term it is probably not to much of a problem. It will make you eat less and you will lose weight.
"But in the long-term we just don't know how healthy it is and it actually might not reduce our risk of heart disease and cancers."
Wendy Greenroyd, who has been dieting since she was a teenager, has tried numerous different diets.
She is against diets which involve cutting out whole food groups and now simply watches her calorie intake.
"If you restrict yourself something you always want it which is why counting calories is so good because you are not restricted.
"You just decide what you are having one day at a time."