Will Drinking Diet Soda Really Make You Gain Weight?

It’s pretty obvious that drinking diet soda isn’t good for you, but is it the culprit of your expanding waistline or of your inability to shed pounds?

upclose soda

You’ve probably seen countless stories that diet drinks cause weight gain, and this theory is mainly product of a couple of popular research studies’ findings. One study by scientists at the University of Texas followed more than 3,600 people for seven to eight years and recorded their average consumption of artificially-sweetened drinks during that time. They found that, the more diet drinks a person consumed, the higher body mass index (BMI) and risk of obesity.

Those scientists also conducted a similar study published in 2015 in which they examined 749 people for nine years. The number of fizzy drinks each person drank were recorded, as well as whether or not those drinks were of the diet variety. This study found that those who had at least one diet drink per day grew at least three inches around their waists and that a direct correlation was found between the frequency of drinks consumed with inches grown.

It appears that this correlation proves that diet soda directly causes weight gain, but that may not be true.


A couple of issues with these findings keep researchers from proving that diet soda leads to weight gain. Most importantly, the people who participated in these studies weren’t monitored or asked to report anything but their beverage consumption. That means that other unhealthy habits could have caused the participants’ expanding waistlines, not (just) diet soda.

To cut this doubt, the 2015 study adjusted statistically for variables that could affect the correlation. They accounted for a variety of starting waist sizes, exercise levels, smokers and non-smokers. Because of this, they claim that there is an “independent effect of diet soda consumption on waist circumference change over time,” says Dr. Hazuka, senior author of the study. He refers to the correlation as being in a “dose-response manner.”

Still, because the diets of these individuals were not monitored or controlled, the findings do not prove causation.


Shape’s “Diet Doctor” Mike Roussell, PhD, suggests looking at your diet as a whole rather than picking apart single habits. “If diet soda is going to be your one vice, that’s fine. I’d rather you drink that than a high-calorie beverage, but limit your consumption to one per day at most,” he said.

So if you’re eating well and exercising regularly, that one diet drink isn’t going to make you gain weight. But be mindful of your choices and don’t let that single sip turn into a junk food binge! Remember, diet soda may be zero-calorie, but it’s not water. It doesn’t hydrate your body and shouldn’t be your go-to drink. Before indulging in your diet drink, be sure to drink at least 64 ounces of water throughout the day!