High-protein diets can accelerate kidney disease in those at risk, researchers have found.
Brad and Jen are said to be devotees of the Atkins diet
Diets which are high in meat proteins, such as the increasingly popular high-protein, low carbohydrate Atkins diet, could overload the kidneys, they say.
People on diets such as the Atkins, said to be followed by stars such as Brad Pitt and Jennifer Anniston and Geri Halliwell, 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.
Nutritionists have already expressed concern that such diets, which can also be high in fats, can cause long-term health problems including raised cholesterol levels.
People who are thinking of trying one of these diets should go to their GP
Elizabeth Ward, British Kidney Patient Association
US researchers followed 1,624 women aged between 42 and 68 were monitored over 11 years.
It was found 489 had a mild kidney problem.
Women were asked to fill out questionaires about their eating habits to see how much protein they ate.
They were also asked about other factors which could influence their kidney health such as age, weight, height, diabetes, high blood pressure, cholesterol levels and smoking and alcohol habits.
The researchers also took blood samples to evaluate kidney function.
The researchers found that in women who had normal kidney function, there was no link between high-protein diets and a decline in renal function.
But those who already had a mild kidney problem who ate a high-protein diet, particularly one high in meat protein, showed some deterioration.
Dairy or vegetable protein was not linked with worsening kidney function.
Public health implications
Proteins need to be broken down by the body into amino acids, and waste products filtered out of the bloodstream and excreted.
Eating too much protein is believed to put too much strain on the body's ability to deal with waste products, particularly in people who already have a kidney problem.
Severe kidney disease can require treatment with dialysis and even a transplant.
Eric Knight led the research at the Brigham and Women's Hospital and Harvard School of Public Health in Boston, Massachusetts.
He told a national newspaper: "The potential effects of dietary protein consumption on renal function on persons with mild renal insufficiency have important public health implications given the prevalence of high-protein diets."
'Tired and lethargic'
Sarah Stanner of the British Nutrition Foundation told BBC News Online: "There have been some concerns about these kind of diets for some time.
"The Atkins diet is the most popular, but there are quite a few which have the same principles.
"They go against what we have been saying for quite a long time. We are trying people to eat more carbohydrates, fruit and roughage.
"People on these diets do tend to lose weight because they are restricting what they eat.
"But they make people feel quite tired and lethargic, so the advantage is that people tend not to stick to them for a long time."
Elizabeth Ward, founder and president of the British Kidney Patient Association said: "If you have healthy kidneys, you can't eat enough protein to damage your kidneys.
"But there are a number of kidney diseases, which do not produce symptoms until much later on in the illness.
"People who are thinking of trying one of these diets should go to their GP for a urine test which would pick up 90% of problems."
The research is published in the Annals of Internal Medicine.