By Caroline Ryan
BBC News Online health staff in Berlin
Eating a high protein diet - such as Atkins - could reduce a woman's chances of conceiving, researchers suggest.
Meat is a good source of protein
The Colorado Center for Reproductive Medicine carried out tests which showed that if mice ate a diet containing 25% protein, it would affect embryo and foetal development.
They told a Berlin fertility conference this could mean women eating over 30% protein may have trouble conceiving.
But an Atkins spokeswoman said they had seen cases where the diet improved women's chances of becoming pregnant.
She said the diet did not set limits on how much protein people should eat.
The researchers fed female mice diets with either a high proportion of protein (25%) or a normal proportion (around 14%).
It was found those on the high protein diet had four times the amount of ammonium in their reproductive tracts than those on a normal diet.
Previous research had shown that high levels of ammonium can damage mouse embryos and impair foetal development by affecting a key gene - H19 - involved in controlling growth.
The gene is only supposed to be activated if it is inherited from the mother. But in two-thirds of embryos from mice on high protein diets, it was the father's HI9 gene that was switched on.
These embryos were later unable to develop properly in the womb.
In this study, 174 embryos at an early stage of their development were transferred from both groups of mice to surrogate mothers fed a normal diet.
This study found that just over a third of embryos developed in mothers on the high-protein diet, compared with 70% in the normal diet group.
Sixty-five per cent of the high-protein embryos developed into foetuses, compared with 81% from the normal diet group.
And while virtually all the embryos from that group continued to develop, just 84% of those from the high-protein group continued the same progress.
The research team said these findings, along with similar research in cows, meant it would be "prudent" for women who were trying to conceive to limit their protein intake to around 20% of their diet.
Dr David Gardner, who led the study, told BBC News Online: "The rate of foetal development was severely reduced as a result of the high protein diet of the mother."
He said caution was needed in interpreting the data, because the study looked at mice which are herbivores.
But he added: "You can extrapolate these findings.
"It's conceivable that people who have protein intakes greater than 30% may have problems conceiving."
But a spokeswoman for Atkins Nutritionals said: "The study subjects were mice, which are herbivores. Whether or not these findings or effects would apply to humans, who are omnivores, is unknown."
She said other research had shown that reducing carbohydrate levels, as advised by the Atkins diet, could help overweight women with polycystic ovary syndrome to conceive.
The research was presented at a meeting of the European Society of Human Reproduction and Embryology.