Medics from New York, writing in the Lancet, describe a 40-year-old woman on the Atkins diet who developed dangerously high acids in her blood.
Public health doctors writing in the journal said low carb diets were "far from healthy".
But a spokeswoman for the Atkins Foundation said the diet would not cause such health problems.
The patient treated by the New York team was obese.
She had been following the Atkins diet rigorously in order to lose weight and had taken recommended precautions, including using vitamins and other supplements.
Technorati Tags
News Health Low Carb Atkins Diet supplements Vitamins Obese