Plenty of women still drink diet sodas–even when pregnant. Then again, how bad can they be since they’re not on the disallowed list? As it turns out, pretty bad actually. Diet soda should be one more thing you give up during pregnancy if you haven’t already abandoned them in general. New research suggests that even if you’re not concerned about your own health, they may contribute to excess weight for your child if you drink them when pregnant.

The study, which was conducted at the University of Manitoba in Winnipeg, Canada, found that women who drink artificially sweetened beverages daily during pregnancy have double the risk of their infants being overweight by their first birthday.¹ Azad, Meghan B.; et al. “Association Between Artificially Sweetened Beverage Consumption During Pregnancy and Infant Body Mass Index.” JAMA Pediatrics. 9 May 2016. Accessed 18 May 2016. http://archpedi.jamanetwork.com/article.aspx?articleid=2521471 The subjects were 3,033 women who were pregnant between 2009 and 2012 with their babies. Each of the women completed a survey during pregnancy that focused on their typical eating habits since conception.

The participants reported the frequency of their consumption of all kinds of beverages, including diet sodas, tea or coffee with artificial sweetener added, and drinks like regular sodas and coffee or tea sweetened with sugar or honey. The moms and infants were tracked after the babies were born, and the body mass index (BMI) of the children was measured at the one-year mark.

After evaluating the data, the scientists determined that drinking artificially sweetened beverages every day was linked to twice the likelihood of having a child who was overweight at 12 months old. This association was reduced after the researchers adjusted for maternal BMI and was further reduced after adjustment for additional variables including total maternal energy intake, diet quality, smoking, diabetes, education, infant sex, birth weight, breast-feeding duration, and solid food introduction. However, even after full adjustment, daily consumption of artificially sweetened beverages remained significantly associated with increased infant BMI. Surprisingly, there was no correlation discovered between daily consumption of sugar-laden drinks and overweight babies.

The investigation did not prove cause and effect, it only found an association between the artificial sweetener and overweight kids. There was no attempt to determine why this might affect the babies’ weights; however, the researchers had some idea about possible causes. Artificial sweeteners were shown in a 2014 study at the Weizmann Institute of Science in Rehovot, Israel to alter the bacteria present in an adult’s microbiome and contribute to glucose intolerance.² Suez, Jotham; et al. “Artificial sweeteners induce glucose intolerance by altering the gut microbiota.” Nature. 9 October 2014. Accessed 19 May 2016. http://www.nature.com/nature/journal/v514/n7521/abs/nature13793.html#affil-auth

This would likely change an individual’s metabolism, and it also might affect which bacteria are passed to the baby during birth. In fact, a 2013 study at the University of Alberta in Edmonton, Canada found that based on the types of bacteria passed from mother to baby during the birthing process, the microbes present in babies’ guts can vary greatly for years to come and potentially impact the risk of developing numerous conditions over time.³ Azad, Meghan B.; et al. “Gut microbiota of healthy Canadian infants: profiles by mode of delivery and infant diet at 4 months.” CMAJ. 11 February 2013. Accessed 19 May 2016. http://www.cmaj.ca/content/185/5/385

The current research was limited by the self-reporting of the volunteers since it is possible that what they wrote they had consumed in the food questionnaire might not be entirely accurate. They might misremember or might not want to admit to the true number of diet sodas and the like they were drinking. But ultimately, whether you’re pregnant or not, this is just one more reminder that using artificial sweeteners is simply bad for your health. They have already been linked to weight gain, diabetes,⁴ Swithers SE. “Not-so-healthy sugar substitutes?” Curr Opin Behav Sci. 2016 Jun;9:106-110. http://www.ncbi.nlm.nih.gov/pubmed/27135048 and depression in adults in various studies, and should be avoided entirely if possible.

Water should be your go-to beverage every day, especially during pregnancy. Keep a glass by your side to ensure you’re drinking throughout the day and remain well hydrated all nine months long. Having diet sodas and other artificially sweetened drinks is just not worth any potential health risk to you or to your baby.