Cardiologist Robert Atkins, a diet expert, was in a critical condition with head injuries after a fall outside his New York office, his spokesman Richard Rothstein said.
Brad and Jennifer are said to be devotees of low-carb diets
Doctor Atkins underwent surgery at the Cornell University Medical Centre after slipping on an icy pavement in Manhattan on Tuesday.
Dr Atkins shot to fame with his Atkins diet, a low-carbohydrate, high-protein eating regime that is supposed to lead to weight loss.
Mr Rothstein said: "Dr Atkins suffered severe head trauma and required surgery. He is currently under medical observation."
He added that doctors described the 72-year-old's condition as "very serious".
Followers of the Atkins diet are allowed to eat unlimited meat, eggs, fish and shellfish.
But they can only eat small amounts of carbohydrates, such as bread, potatoes and pasta.
The diet is said to promote rapid weight loss because it forces the body to burn stored fat instead of carbohydrates.
It has proved controversy because it challenges many long-held
tenets of nutritional theory.
Recently, United States researchers found high-protein diets can accelerate kidney disease in those at risk.
In a survey of women aged between 42 and 68, women who already had a mild kidney problem and ate a high-protein diet, particularly one high in meat protein, showed some kidney deterioration.
Other critics say diets with lots of meat eating and high in
protein are linked to diseases such as osteoporosis and heart
Stars such as Brad Pitt, Jennifer Anniston and Geri Halliwell are all said to be on Atkins-type diets.