One in four GPs say they would advise patients to stay fat rather than try the Atkins diet, suggests a poll.
Millions follow the Atkins diet
Some dieticians say that the low carbohydrate diet plan is not healthy in the long term.
However, there is no firm evidence that the Atkins plan damages health - while being obese is certainly harmful.
The survey, by doctor's website Onmedica, revealed that one in ten GPs had actually tried the controversial diet themselves.
A third of those questioned said that they would recommend Atkins in certain circumstances.
One in three adults in the UK is now overweight or obese, and obesity is a major risk factor for the development of diabetes, and can lead to heart disease.
The Atkins diet has become popular because many who have tried it have reported significant weight loss within weeks of starting the plan.
GPs are a source of information for people considering the Atkins diet - four out of five of the 189 polled said that patients had consulted them about it.
However, 29% of those surveyed said that they would rather their patient was obese than they tried the Atkins diet.
They suggested that long-term effects on cholesterol levels, coupled with the possibility of mineral deficiences and the impact on the liver and kidneys should rule out the diet.
One said: "It is totally in opposition to all the healthy eating principles that I promote to my patients - reduce fat, plenty of fruit and vegetables, with the emphasis on complex carbohydrates."
Dr Luke Koupparis, from Onmedica, said: "Family doctors are constantly being asked about the diet by patients, but there is little information about its safety.
"So the majority are advising caution. The message from GPs seems to be that a proper balanced diet is much better for promoting weight loss and long-term health."
A spokeswoman for Atkins Nutritionals, which markets the diet in the UK, said that advising an obese patient to avoid the Atkins diet was "irresponsible".
She said: "We know obesity to be life-threatening while no studies have shown Atkins to be such, so to denounce a working solution to this criris contradicts their duty to society."