The Atkins diet calls for restricting carbohydrates to achieve weight loss, then gradually adding them back in. However, many people who say they're following the diet actually eat large amounts of protein and fat.
Doctors from New York University wrote in The Lancet journal of a 40-year-old woman who developed a dangerous condition called ketoacidosis, a buildup of acids called ketones in the blood which can lead to patients falling into a coma.
However, some outside experts said the case is rare and does not reflect a major health threat associated with low-carb diets.
"I think this is an isolated case. The idea that serious ketoacidosis could be triggered by a low-carb diet does not happen very often," said Dr. Paul Clayton, president of the forum on food and nutrition at the Royal Society of Medicine in London.
Dr. Abby Bloch, vice-president of programs and research at the Dr. Robert C. Atkins Foundation - a medical research charity run by Atkins' widow, Veronica - said ketoacidosis was not triggered by diet and could only occur if the patient had an "abnormal clinical metabolic condition."
"It is not brought on by diet unless she had an underlying cause which she and her doctors weren't aware of," Bloch said.
"Ketoacidosis is an abnormal state that occurs when there is a clinical abnormality. It doesn't occur when there's a normal state like a low-carb diet."
The patient, who was not identified, was admitted to an intensive care unit for four days after becoming short of breath. Before being hospitalized, she had lost her appetite, felt nauseous and was vomiting four to six times a day, the doctors wrote in the paper.
Tests confirmed ketoacidosis.
Ketones are produced in the liver when insulin levels fall due to starvation or diabetes.
"Our patient had an underlying ketosis caused by the Atkins diet ... This problem may become more recognized because this diet is becoming increasingly popular worldwide," said Professor Klaus-Dieter Lessnau, who led the team from the New York University School of Medicine.
Clayton said that the main problem of high protein diets is in the strain they put on kidneys and the risk of renal failure.