High-protein diets of the kind popularised by Robert Atkins may reduce a woman’s chance of conceiving, according to a study presented at a fertility conference.

The research - conducted on mice - found that a diet containing 25 percent protein disrupted the normal genetic imprinting pattern in early embryos. It also had an impact on embryos that were transferred to other uteruses.

Although mice are herbivores and humans are omnivores, the findings “may have implications” for women who want to have a baby, said researcher David Gardner, scientific director of the Colorado Center for Reproductive Medicine, which carried out the study.

“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 percent of total energy consumption.

“The available data certainly indicate that a high protein diet is not advisable while trying to conceive,” he said in a press release issued Monday.

ART is the usual term for in-vitro fertilisation (IVF) - a “test-tube” baby.

Previous research, conducted on cows and mice, showed that protein levels in diet affect levels of ammonium in the female reproductive tract of those animals.

This is important, because ammonium is known to adversely affect mouse embryos developed in culture.

Exposure to high levels of ammonium alters the imprinting of a key gene, H19, inherited from the mother, that helps to directs foetal growth and development.

Gardner’s research explored this path by giving a batch of mice a diet with a “moderately high” proportion (25 percent) of protein. Another batch was the “control” group and fed a diet comprising 14 percent protein.

The mice were mated. Forty-two fertilised eggs, called blastocysts, were examined to examine to see if their H19 gene was being properly imprinted.

Embryos receive copies of most genes from both parents, and imprinting causes a gene from just one parent - and not the other - to be switched on.

If both gene sets are switched on, development can go haywire. Imprinting flaws are widely blamed for foetal malformations and the extremely high rate of spontaneous abortions among cloned farm animals.

Another 174 blastocysts from the two batches of mice were transferred to mice who were fed a normal diet.

Only 36 percent of blastocysts that had developed among mothers on the 25-percent protein diet had a normal imprinting pattern, Gardner said.

That compared with 70 percent in the control group.

Sixty-five percent of the embryos in the high-protein group developed into foetuses once they had been transferred, whereas the tally into control group was 81 percent.

There was also some evidence of flawed foetal development. Foetuses from the high-protein group were a third of a day behind the control group in their development, and one foetus had a neural tube defect.

The research was presented at the annual coonference of the European Society of Human Reproduction and Embryology (ESHRE).

The 14 percent figure for the “control” diet is equivalent to the level in the average American diet.

The most popular diet in the world today and the latest in a historical series to encourage high-protein foods, the Atkins requires followers to ditch carbohydrate-rich foods such as pasta, potatoes, wheat and rice and instead tuck into beef, chicken and eggs and other protein-laden foods.

It does not set limits on how much protein people should eat but emphasises reducing carbohydrate intakes.

Atkins Nutritionals, which markets the diet plan, says about 25 million Americans are on the diet and nearly 100 million are adhering to some sort of “controlled carbohydrate” regimen.

Asked by AFP to react to the research, Atkins Nutrionals’ medical director Stuart Trager said the research was conducted on herbivores, “and it’s troubling to jump to conclusions that the same can apply to humans.”

In addition, Trager said, there was evidence that by reducing their carbohydrates, some overweight women with polycystic ovary syndrome, a leading source of infertility, had been able to conceive.