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Half-baked coverage of potatoes and gestational diabetes

Baking potato, side viewThe humble potato made big news twice this week. In one instance, a photograph of an unwashed potato sold for $1.5 million (Australian) to a collector. You can see a representation of the image here, for free.

Almost as strange, the Washington Post reported that pregnant women should lay off potatoes because eating even one cup a week can increase your risk for gestational diabetes by 20%. Eating five or more servings a week raises the risk a whopping 50%. “If you’re planning to become pregnant, you might want to lay off the potatoes” reads the headline.

A number of other news outlets posted similar stories suggesting that spuds might not be safe for pregnant women:

Gestational diabetes is nothing to laugh at. It puts both the mother and child at risk during delivery, and it’s linked to Type 2 diabetes later on. But an observational study based on biannual dietary questionnaires designed to track disease outcomes and lifestyle factors — not diet during pregnancy — doesn’t hold water. Especially when the study didn’t track weight gain which is a major culprit in gestational diabetes and Type 2 diabetes.

Never mind the fact that this type of study can’t prove cause and effect, so it’s just not accurate to state, as the Post story does, that eating potatoes “raises risk” for the condition.

Of course, the Washington Post would have avoided coming off half-baked if it had reached out to at least one nutrition researcher with no connection to the study.

Enter Yoni Freedhoff, MD, an assistant professor of family medicine at the University of Ottawa, medical director of the Bariatric Medical Institute and frequent contributor.

“Putting aside the many well established questions and concerns arising from food frequency questionnaires’ abilities to accurately assess the intake of single foods, what strikes me the most is the fact that the study wasn’t designed to explore diet during pregnancy, just diet over time, including pregnancies. Yet many women change their diets after learning about their pregnancies – some because of their tastes changing, and some because their pregnancies lead them to worry about the healthfulness of their diets in ways that they didn’t before they had a baby to consider. If conclusions are going to be drawn about diets in pregnancy, studies need to look at diets in pregnancy. Moreover, if what’s being studied is the risk of gestational diabetes, to not control for gestational weight gain strikes me as a methodologically insurmountable oversight if strong conclusions are to be made or press releases to be posted.”

Granted, both the Washington Post article and the BMJ news release that sparked it mention some limitations to the study at the very end, including the fact that weight gain wasn’t assessed by the researchers. But the headline and the first few paragraphs are sensationally misleading — and that’s the message that most readers will read and remember, and which they’d probably be better off forgetting.

Kathlyn Stone is an associate editor for and a frequent blog contributor.

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