Last spring, British researchers hit on what seemed like a startling finding: Eating lots of cereal before getting pregnant was associated with conceiving a son. Never mind that sex is determined by chromosomes in the father's sperm. The apparent link between gender and diet generated buzz.
But it turns out cereal may not be your lucky charm if you're hoping for a boy.
Today, another group of scientists is disputing that study, charging that its analysis was flawed and its conclusions due to chance. The researchers—from the National Institute of Statistical Sciences, Cornell University and New York Medical College—report their findings in today's Proceedings of the Royal Society B, the same journal that published the cereal study last April.
The U.S. group re-ran data from the large nutrition survey from which the cereal conclusion was drawn, using a different statistical analysis than the University of Exeter scientists. "By our analysis, it looked like everything was random and there was nothing special about cereal," says Stan Young, assistant director for bioinformatics at the National Institute of Statistical Sciences, an independent, nongovernmental think tank in Research Triangle Park, N.C.
The Exeter study asked some 700 British women to answer a 133-item questionnaire about what foods they ate in the weeks prior to and after conceiving, and then months into their pregnancies. Pre-pregnancy cereal breakfasts were associated with birthing boys.
But in any study with that much data, a small percentage of the results will inevitably show statistical significance just by chance, Young says, and that's likely what happened. Still, the findings of such observational studies (which draw conclusions based on what's observed in a group of subjects, versus measuring the effect of a specific intervention on groups in a randomized controlled study) are replicated only 10 to 20 percent of the time, he says.
"We don’t think that if the study was [repeated] that cereal would show up as significant," he says. "Something else would, just by the chance nature of doing these large, complex studies. We think their analysis is wrong and doesn’t support their claim."
Young added, "It's not biologically plausible that the nutrition of the mother has anything to do with the gender of the child."
Fiona Mathews, the lead author on the cereal study, tells us that she ran her data again using Young's methodology. "We are absolutely confident that our results are statistically robust," Mathews says.
"Sex ratios at birth can be affected by a range of factors including birth order (whether infants are first-born or not), the timing of insemination, and environmental conditions experienced by the mother at conception," she writes in an official response to Young's paper. "The argument of implausibility is therefore erroneous: mothers do, albeit unknowingly, influence the gender of their children.
"We found that eating breakfast cereal, the main breakfast food in the U.K., was associated with having a male infant," she writes. "This may be, as explained our original work, because breakfast cereal is a major contributor to calorie and nutrient intakes, and so it is a 'proxy' marker of high nutrient intakes."
Updated at 1:10 p.m. Jan. 14 with comment from Mathews.
Image © iStockphoto/Jani Bryson