According to the National Post headline, “Eating junk food before getting pregnant spikes risk of premature birth: researchers”.
No, it doesn’t.
The study “Preconception dietary patterns in human pregnancies are associated with preterm delivery” (JA Grieger, LE Grzeskowiak, and VL Clifton) was e-published ahead of print in the Journal of Nutrition (April 30, 2014). They concluded that nutrition before pregnancy was associated with pre-term birth. This was a retrospective, cross-sectional study which means that the 309 pregnant women were surveyed one time about what they ate during the 12 months before they got pregnant. They were never asked about what they ate during pregnancy although they cite other studies showing that the two are typically similar.
Problem 1: The results could just reflect that diet during pregnancy affects risk of premature delivery.
After a lot of complicated analyses, the researchers identified three dietary patterns (high-protein/fruit, high-fat/sugar/takeaway, vegetarian-type) and assigned a score to each woman based on how she compared to the average score. They didn’t categorize mothers into separate groups and compare the incidence of pre-term delivery. The overall pre-term rate is 10%. What is the risk for those eating “junk food”? We don’t know. This type of analysis could result in complete different findings with a different group of moms.
Problem 2: Even the researchers acknowledge in their discussion that the results of this study “may not be generalizable to other populations”.
The article and the headline clearly overstate the findings of this study. I wouldn’t equate an odds ratio of 1.5 to a “spike” in risk. As long as associations are being used to make dietary recommendations, they could have emphasized that the meat-based, high-protein diet was associated with lower risk of pre-term birth while the vegetarian diet showed no benefit.
Health reporters need to make much more liberal use of the words “may”, “might”, “suggests”, etc. and the headline writers need to stop being so sensationalistic.