The gaffe came during a visit to a fire station in Brooklyn yesterday.

Mr Bloomberg was dining with fire fighters and was overheard making off-the-cuff remarks suggesting that the Dr Robert Atkins may have died from weight-related health problems.

When Dr Atkins died last April it was reported that he had succumbed to injuries suffered during a fall on an icy Manhattan street.

The Mayor's remarks were overheard by a reporter from the New York Post. The newspaper reported today that the comments came as Mr Bloomberg was dining on chicken and pasta, a combination that Dr Atkins would have disapproved of.

The Mayor was heard to say to the fire fighters: "Atkins is dead. I don't believe that bulls*** that [Atkins] dropped dead slipping on the sidewalk. Yeah, right!"

Mr Bloomberg went on to describe meeting the diet guru during a fundraising event at the doctor's home: "The guy was fat ... and the food was inedible.

"I took one appetiser and I had to spit it into my napkin. It was just terrible," he added.

The mayor's comments were recorded by a television crew from the local television station New York 1, which played the footage throughout the day, sparking an angry response from the Atkins organisation.

Richard Rothstein, an Atkins spokesman, told the Post that Dr Atkins's widow Veronica was "extremely upset and hurt" by the remarks especially considering Mr Bloomberg sent her a touching condolence letter after her husband's death in which he said the doctor was "an inspiration to us all".

A Bloomberg spokesman said that the event was supposed to be off the record and accused the TV station of "dispensing with journalistic ethics". New York 1 insisted that the mayor had known the cameras and sound recorders were rolling.

The incident came after a warning on Monday from Atkins Nutritionals that followers of the diet should limit their intake of saturated fat and red meat. The low-carbohydrate diet has come in for criticism for promoting high meat and fat intake over fruit, vegetables and whole grains.

The British Nutrition Foundation and the British Dietetic Association both advise against the diet, and the Food Standards Agency recently issued a health warning about low-carbohydrate diets.

Following pressure, promoters of the plan are now advising that only 20 per cent of a dieter's calories should come from saturated fat.

Colette Heimowitz, director of research and education for Atkins Nutritionals, said that the revision had been made because the company wanted health experts and dieters to "feel comfortable with this diet".

Ms Heimowitz has been making the clarification - which flies in the face of conventional perceptions of the diet - at recent health seminars.

The diet purports to work on the principle that cutting out carbohydrates will reduce concentrations of insulin, which converts sugars to energy and stores any excess as fat.

But recent scientific studies have indicated potential dangers ranging from painful kidney disorders to heart disease, as well as bad breath.

Although Atkins devised the diet more than 30 years ago, it has recently become a worldwide phenomenon.

The BBC Television science programme Horizon tonight examines the claims made by Atkins supporters and critics. It concludes that the diet does work – by making people feel more full and therefore eat less – and that it does not lead to excess dangerous cholesterol.