Eating Potatoes Before Pregnancy Linked to Gestational Diabetes

Veronica Hackethal, MD

January 13, 2016

A study drawing from data on over 15,000 women participating in the Nurses' Health Study suggests that women who ate potatoes up to five times a week before pregnancy had an increased risk of gestational diabetes, compared with those who ate fewer potatoes (ie, less than one serving per week).

The research also finds that substituting other vegetables, such as legumes (peas and beans), and/or whole grains for potatoes may decrease this risk.

"Potatoes are related to deteriorated glucose response and a higher risk of diabetes in pregnancy when consumption levels are high," commented lead author Cuilin Zhang, MD, PhD, senior investigator in the epidemiology branch at the National Institutes of Health, Rockville, Maryland.

Dr Zhang and colleagues published their work online January 12 in the BMJ.

There is controversy about the categorization of potatoes. The newly released 2015–2020 Dietary Guidelines for Americans places potatoes within the vegetable category, whereas UK guidelines group potatoes into the "starchy-food" group. However, both sets of guidelines endorse potatoes as a healthy food.

While potatoes are rich in several important nutrients, like vitamin C, potassium, fiber, and some types of protein, a recent related analysis of data from the Nurses' Health Study linked higher potato consumption with increased risk of type 2 diabetes; this risk was particularly heightened when the potatoes were served in the form of french fries.

The argument is that high levels of starch in potatoes are quickly absorbed, leading to a rapid spike in blood glucose levels.

Dr Zhang said: "Potatoes may not be regarded as healthy vegetables, as they are rich in starch, especially when they are consumed at high levels. In the guidelines, potatoes are categorized as starchy vegetables, which is true. However, the health impact of vegetables may be type-specific."

"Given that potatoes are widely consumed worldwide, understanding the association between consumption and risk of gestational diabetes has important clinical and public-health implications," he and his colleagues observe. The findings "from the present study raise concerns" about US and UK guidance to consume plenty of potatoes, they assert.

However, Keith-Thomas Ayoob, EdD, RD, FAND, a nutritionist and associate clinical professor at Albert Einstein College of Medicine, New York, disagrees. "When you demonize one food you pull your focus from the whole picture, which is where good health and balance really live."

He asserted that there are many limitations to the current study, including most importantly the fact that the work did not investigate the impact of weight gain during pregnancy. "The main issues pertaining to gestational diabetes and diet are overall diet quality and controlling portion size."

Do Potatoes Independently Increase Risk for Gestational Diabetes?

Gestational diabetes represents a common problem of pregnancy and may increase the risk of later type 2 diabetes in the mother as well as her offspring. Studies about the impact of diet just prior to and during pregnancy on women and babies are limited, and more research is needed on this topic, Dr Zhang pointed out.

The current prospective cohort study looked at 15,632 women who were part of the Nurses' Health Study and became pregnant between 1991 and 2001.

Participants were over 90% white and had no past history of gestational diabetes or chronic diseases like type 2 diabetes, cardiovascular disease, or cancer before becoming pregnant.

Researchers assessed potato consumption in the previous year every 4 years using self-reported food frequency questionnaires. They evaluated total potato consumption by adding together baked, boiled, and mashed potatoes and french fries

They also developed a diet score to evaluate overall diet quality, which included assessment of intake of sugar-sweetened beverages, sodium, alcohol, and other foods that have been associated with diabetes.

Women also self-reported diagnoses of gestational diabetes, 94% of which were confirmed by checking medical records.

Over the 10-year period, 854 women developed gestational diabetes in 21,693 singleton pregnancies.

Results adjusted for risk factors including age, diet quality, exercise, body mass index (BMI), and family history of diabetes showed the relative risks of gestational diabetes for total potato consumption of one, two to four, and five or more servings per week, compared with less than one serving per week, were 1.20, 1.27, and 1.50, respectively (P=0.006 for trend).

The researchers also examined the association between risk of gestational diabetes and different types of potato preparations — for eating baked, boiled, or mashed potatoes before pregnancy, there remained a significant association between frequency of ingestion and risk of diabetes, even after adjustment for prepregnancy BMI.

Consumption of french fries was also significantly linked to gestational diabetes, but this relationship became nonsignificant after adjustment for BMI.

Substituting other vegetables, legumes, and whole grains for two servings of potatoes per week lowered the risk of gestational diabetes by 9% to 12%.

The results did not change when accounting for overall diet quality and individual foods linked to diabetes, suggesting that potatoes may independently increase the risk for gestational diabetes, according to the authors.

They do note several limitations, however, including the observational nature of the trial, which precludes conclusions about whether potatoes actually cause gestational diabetes.

Future intervention studies and randomized clinical trials are needed to further investigate these findings, they conclude.

Too Many Limitations: Potatoes Are a "Super Good Food"

This last point is key, says Dr Ayoob. "The study is observational, which means that it's hypothesis-generating. I would need clinical data to take the study seriously," he told Medscape Medical News.

In addition, the work did not evaluate weight gain during pregnancy, which is a near "fatal flaw," continued Dr Ayoob, who admits to being a fan of baked and roasted potatoes. "That really weakens things in a study about gestational diabetes and diet."

He maintains that potatoes are "one of the best sources of nutrients, potassium, and good-quality protein" and "a super good food."

"Anybody who's got gestational diabetes didn't get it because of potatoes," he asserted. "If you have gestational diabetes you better watch your total diet, period. Of course, going after one food is easier."

The authors and Dr Ayoob report no relevant financial relationships.

BMJ. Published online January 12, 2016. Article


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