Pregnant Women Who Drink Diet Soda Have Fatter Kids

A new study from the National Institutes of Health finds that children born to certain women who consumed at least one artificially sweetened beverage a day while they were pregnant were more likely to be overweight or obese by age 7 compared to the children of moms who drank water. That's important because childhood obesity can increase health risks later in life, including the risk of diabetes, heart disease, stroke, and some cancers. And it's another indicator that "diet" beverages aren't a healthier option—even while the exact relationship between artificial sweeteners and weight gain remains unclear.

For their study, published in the International Journal of Epidemiology, researchers relied on the Danish National Birth Cohort, which uses long-term data about pregnancies among more than 91,000 women in Denmark from 1996 to 2002. The women filled out a detailed questionnaire about their diet in the 25th week of their pregnancy and children's weight at birth and at 7 years old were also included. Researchers compared data among women who said they drank artificially sweetened beverages including diet soda, those who drank sugar-sweetened beverages, and those who drank neither. (The authors note that pregnant women tend to increase their fluid intake as the volume of amniotic fluid increases; to cut calories, some women replace sugar-sweetened drinks with artificially sweetened ones.)

The study authors focused on more than 900 pregnancies where the mother developed gestational diabetes, a form of high blood sugar that occurs only during pregnancy. Among that group, about 9 percent of women said they consumed at least one artificially sweetened beverage every day. Children born to those mothers were 60 percent more likely to have a high birth weight compared to those born to women who never drank sweetened beverages.

That difference continued into the children's early life: at age 7, those whose mothers drank artificially sweetened beverages daily were nearly twice as likely to be overweight or obese. Interestingly, kids born to moms who drank a daily sweetened beverage—whether sugar-sweetened or artificially so—were equally likely to be overweight or obese at age 7. Children whose mothers drank water instead had a 17 percent lower risk of obesity at age 7.

"Our findings suggest that artificially sweetened beverages during pregnancy are not likely to be any better at reducing the risk for later childhood obesity than sugar-sweetened beverages," Cuilin Zhang, the study's senior author and an epidemiologist at the National Institute of Child Health and Human Development, said in a statement. "Not surprisingly, we also observed that children born to women who drank water instead of sweetened beverages were less likely to be obese by age 7."

It's not clear why drinking artificially sweetened beverages may increase obesity risk compared to drinking water. The authors cite one animal study which suggests that changes among microbes in the digestive tract may be to blame; another examined whether artificial sweeteners could increase the intestines' ability to absorb glucose. Other evidence showed that artificial sweeteners desensitized rodents' digestive tracts, making them feel less full and more prone to overeating. (Think about it: your brain senses something sweet but doesn't get any calories out of it, so it nudges you to eat more.)

As always, more research is needed. The study authors note that breastfeeding, diet, and physical activity levels can all affect children's weight; it's not definitive that drinking artificially sweetened drinks causes children to be overweight. (People who like soda could have a sweet tooth overall.) But they also note that consumption of those kind of beverages is on the rise, and we've already connected them to weight issues. All of us, pregnant or not, could stand to lay off the soda.

Read This Next: Here's Another Reason You Might Want to Quit Diet Soda