In a presentation Monday to a European fertility group, researcher David Gardner, PhD, reported impaired implantation of a fertilized egg and disrupted embryo development in a group of female mice fed a diet containing 25% protein, when compared with mice who ate a diet that containing 14% protein -- an amount that is recommended by the American Heart Association and the National Cholesterol Education Program.
Eating a high-protein diet also seemed to disrupt a process known as imprinting, which controls which inherited genes become active.
"I certainly would not say that based on this research women should abandon high-protein diets to improve their chances of conceiving, but it is clear that human studies are needed," Gardner tells WebMD.
Ammonium and H19
Millions of women of childbearing age have turned to high-protein, low-carbohydrate eating plans like the Atkins diet to shed some pounds. These diets generally recommend dieters receive 30% to 50% of their total calories from protein.
But Gardner says the popularity of these diets was not the catalyst for his research. Instead, it was his own studies in mice, begun a decade ago, and other studies in cows showing that protein in the diet affects levels of the chemical ammonium in the female reproductive tract. Gardner showed that ammonium can inhibit imprinting of the gene H19, which has been shown to be important for growth, in mouse embryos.
In his latest study, Gardner and colleagues at the Colorado Center for Reproductive Medicine fed female mice diets containing either 25% or 14% protein for four weeks prior to mating. Following mating, embryos from mothers on both diets were examined for imprinting. They were later transferred to the wombs of mice eating normal diets to see the effects of the diet on embryo development prior to implantation.
The researchers found that 36% of the embryos from the mice on the high-protein diets developed normal imprinting, compared with 70% of the embryos from mice fed less protein.
The researchers also showed that just 65% of the embryos from the high-protein group developed into fetuses, compared with 81% of the embryos from the low-protein mice. Of those embryos that did develop into fetuses, the researchers found a significant delay in development in the high-protein group.
Mice Don't Eat Steak
Mice, being herbivores, normally eat very little protein, and Gardner cautions against making too many assumptions about the impact of a high-protein diet on human fertility.
Atkins Nutritionals spokesman Stuart Trager, MD, is more emphatic in making the point.
"I think the one thing that can be said from this research is that mice who want to get pregnant should not be following this diet," he tells WebMD. "But extrapolating this to humans, who are not herbivores by nature, crosses a line that I think is rather inappropriate."
Trager, who serves as medical director for Atkins, says women who are pregnant or nursing should not be on a low-carbohydrate diet or any other weight loss plan without medical supervision. As for women who are trying to become pregnant, he points to studies showing that a low-carbohydrate diet may actually help those with a particular type of infertility to conceive. Women with the condition known as polycystic ovary syndrome tend to be overweight and have insulin resistance.
"The benefits of controlling carbohydrates in the treatment of this condition are becoming more recognized," he says.
But infertility expert Amos Grunebaum, MD, says, as a rule, women who want to become pregnant should eat like they already are. In other words, they should eat a nutritionally balanced diet, take a multivitamin that includes folic acid, and avoid alcohol. Those who want to lose weight should also exercise daily, he says.
"Any weight loss diet that restricts whole food groups should be avoided," he tells WebMD. "Eating a well-balanced diet is very important during pregnancy and when a woman is trying to conceive. There are plenty of diets out there that allow you to do this and still lose weight."