It's one of the first questions asked by many women hoping to get pregnant: "What should I eat in order to boost my fertility?"
A new study offers up one possible answer, claiming that women who ate a diet rich in protein and low in carbohydrates while undergoing in vitro fertilization had higher pregnancy rates than those whose ratio of protein to carbs was the inverse.
But the findings, while provocative, are highly preliminary.
"Protein is essential for good quality embryos and better egg quality, it turns out," study researcher Dr. Jeffrey Russell, director of the Delaware Institute for Reproductive Medicine, said in a statement. His research was released at the American College of Obstetricians and Gynecologists' annual clinical meeting in New Orleans on Monday.
Patients whose protein intake represented 25 percent or more of their daily diet, and whose carbohydrate intake was 40 percent or less, had pregnancy rates four times higher than those who ate less protein and more carbs while undergoing in vitro fertilization (the joining of a woman's egg and a man's sperm in a laboratory before transferring the resulting embryo to her womb).
Researchers asked 120 women undergoing IVF to keep a three-day nutritional journal before they had an embryo transfer. Forty eight women had an average daily protein intake greater than 25 percent, while 72 had an average intake under 25 percent. (The Centers for Disease Control and Prevention says it is generally recommended that people get between 10 and 35 percent of their daily calories from protein.)
There were no differences in body mass index (a measure of weight relative to height) between the two groups, and because of that, the researchers concluded that improving fertility may be linked to specific nutritional components in a woman's diet, more than to her overall BMI.
But Dr. Kathy Hoeger, Director of the Strong Fertility Center at the University of Rochester, N.Y., said that other factors might have affected the outcomes among the high-protein, low-carb group. Hoeger did not work on the new study.
"We don't have enough information about other factors," she told The Huffington Post.
"The question about high protein, low carb is still very uncertain with regard to fertility," Hoeger added, explaining that good scientific research on the links between diet and fertility is scant. Much of what is known has been extrapolated from preliminary animal studies, and the mechanisms that link nutrition and egg quality are not well understood.
But the desire for more information is there, evident in the numerous books, blog posts and articles on the topic.
"As a practicing fertility doctor, probably the first question every one asks me is, 'What should I be eating?'" Hoeger said. "Clearly this is something on people's minds."
Perhaps the most scientifically rigorous information available comes from a 2007 study, led by researchers at Harvard University, that used data from more than 18,000 women who participated in the Nurses' Health Study, one of the longest-running investigations into women's health in the U.S. Those findings were detailed in the much-hyped book "The Fertility Diet," which offered dietary guidelines for preventing and reversing ovulatory infertility (but not infertility resulting from issues like blocked fallopian tubes).
According to the Harvard researchers, women should avoid trans fats and focus on the quality of the carbohydrates they eat, opting for fiber-rich foods and avoiding simple sugars rather than restricting the quantity of carbs. Researchers also found that women who had more full-fat dairy products in their diets were less likely to have problems getting pregnant than those who opted for skim or low-fat options.
And that study, like the new ACOG research, has its limitations. Because it was an observational study, researchers were able to look at data from a large group of women and generate hypotheses, but could not test those theories directly.
"Dietary input is important and you can't just ignore it, but we don't know enough to say you should have this percent of carbs, and this percent of protein," said Hoeger. "We do know that extremes of diet are probably harmful."