The high-protein Atkins diet may be damaging the chances of weight-conscious women getting pregnant and having a healthy baby, scientists said yesterday.
They advised those hoping to conceive to switch to more normal eating patterns.
Researchers in Colorado revealed at a European fertility conference that embryos from mice that had been fed a high protein diet showed a failure to implant in the womb. They believe the results should be a warning to women who want children.
"Although our investigations were conducted in mice, our data may have implications for diet and reproduction in humans," said David Gardner, scientific director of the Colorado Centre for Reproductive Medicine in Englewood.
Some 3m people in the UK and 30m in the US are believed to have tried the controversial Atkins diet, which advocates high meat, fish and egg consumption and severely limited intake of carbohydrates such as bread, rice, pasta and starchy vegetables.
Animal research has previously shown that the amount of protein in the diet can affect the levels of ammonium in the female reproductive tract of cows and mice.
Laboratory tests have also demonstrated that ammonium can interfere with the development of mouse embryos. It appears to affect the H19 gene, found on chromosome 7, which is important to growth.
The Colorado team fed mice a diet which contained a relatively high 25% protein. A con trol group were given a diet which was 14% protein.
People trying to lose weight on the Atkins diet tend to consume around 35% protein initially, dropping to 25% later, although Atkins representatives say there is no upper limit to the amount of protein that can be consumed.
"We definitely don't set a limit on how much protein people should eat. It's as much protein as you need to eat until you are full. Protein is quite satisfying so people don't tend to overeat," said a spokeswoman.
In the study, detailed at the European Society of Human Reproduction and Embryology conference in Berlin, only a third of the mice (36%) on the high protein diet developed with a normal H19 gene, as opposed to 70% of the control group.
Of the embryos in the high protein group, only 65% developed into foetuses once they had been transferred to the womb, compared with 81% in the control group.
"Not only did fewer embryos develop into foetuses when transferred from the high protein group, but of all the embryos that implanted, only 84% developed further, whereas in the control group 99% of the embryos that implanted con tinued to develop," said Dr Gardner.
By the 15th day of gestation, foetuses from the high protein group were a third of a day behind the control group in their development.
One foetus had a neural tube defect - damage to that part of the foetus which becomes the spinal cord or brain. In humans the defect most commonly leads to spina bifida.
"These findings, together with similar work carried out in cows, mean that it would be prudent to advise couples who are trying to conceive, either naturally or via ART [assisted reproduction technology], to ensure that the woman's protein intake is less than 20% of their total energy consumption," said Dr Gardner. "The available data certainly indicate that a high protein diet is not advisable while trying to conceive."
A spokesman for Atkins Nutritionals Inc cast doubt on the findings. "It is important to note that there was no mention of carbohydrate control in the research conducted by Dr Gardner," he 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."
Ben Gocial, a reproductive endocrinologist from Thomas Jefferson University Hospital, speaking on behalf of Atkins, said that controlling carbohydrate consumption had been shown to have a positive effect in women who were trying to conceive and who were over-weight and/or not ovulating properly.