Women planning a pregnancy have plenty to think about, and now they can add fried foods to the list.

Fried foods are tasty and, because they taste good, we tend to eat too much of them. This overindulging is linked to an increased risk of overweight and obesity, a pretty reliable indicator of a generally unhealthy diet.

Even worse, the act of frying itself may have undesirable consequences for our health. Those consequences are especially bad for women who are pregnant.

Fried foods may also absorb the potentially toxic by-products created as the fat or oil is degraded during the frying process.

The health effects of frying are not completely understood, but it appears to change the chemical composition of the fats or oils that are used in frying. Healthy unsaturated fats like linolenic or linoleic acid are lost, while the dangerous trans-fatty acids increase with frying. Fried foods may also absorb the potentially toxic by-products created as the fat or oil is degraded during the frying process.

Researchers with the National Institute of Child Health and Human Development decided to investigate a possible connection between fried foods and gestational diabetes (GD). They discovered that women who eat too much fried food before becoming pregnant have a greater risk of developing GD.

Gestational diabetes is a complication of pregnancy that is characterized by consistently elevated blood glucose levels in a woman without previously diagnosed diabetes. The condition usually disappears once the baby is born, but if it goes untreated it can lead to larger than normal babies, complications for the mom during pregnancy and delivery, and an increased risk of problems for the baby after delivery. Later in life, both baby and mother are at increased risk of developing type 2 diabetes.

Researchers used data from the Nurses’ Health Study II and examined over 21,000 single birth pregnancies involving 15,000 women. Diet information, including the intake of fried foods eaten both at home and away from home, was collected using a food frequency questionnaire.

During 10 years of follow-up, 847 cases of gestational diabetes were documented. The researchers adjusted for age, parity, BMI, dietary, and non-dietary factors and found that women who consumed fried foods more than once a week had an increased risk of developing gestational diabetes. The risk more than doubled if they ate it seven or more times a week compared to those who ate fried foods less than once per week.

“Frying…results in significantly higher levels of dietary advanced glycation end products (AGEs), the derivatives of glucose-protein or glucose-lipid interactions,” the authors explained in a statement.

“Recently, AGEs have been implicated in insulin resistance, pancreatic beta-cell damage, and diabetes, partly because they promote oxidative stress and inflammation. Moreover, intervention studies with a diet low in AGEs have shown significantly improved insulin sensitivity, reduced oxidant stress, and alleviated inflammation.”

Foods fried at home were less likely to be associated with GD compared to foods fried in commercial kitchens away from home. That's because oil that is reused, as is the case in so many restaurants and fast-food outlets, deteriorates much more than oils used at home, the researchers believe.

More research is needed to confirm these findings and understand the underlying mechanisms, but in the meantime, prospective mothers will probably want to limit the amount of fried foods they eat, particularly when eating out.

The study is published in Diabetologia. Download this research here.