Are diet sodas really safer? A 14-year study suggests otherwise

We’ve all been there: standing in a supermarket aisle, wondering whether to grab the regular soda or its diet version. You might assume the sugar-free option is the healthier choice, especially if you’re trying to avoid weight gain or reduce your risk of diabetes, right?

Well, a new Australian study, published in Diabetes & Metabolism in May 2025, casts serious doubt on that assumption. The work was led by Dr Robel Hussen Kabthymer of Monash University, alongside colleagues from the University of Adelaide, University Medical Centre Utrecht in the Netherlands, Cancer Council Victoria, the University of Melbourne, and RMIT University.

The study followed more than 36,000 people in Melbourne for nearly 14 years. The goal? To investigate how often people drank sweetened beverages, both sugary and artificially sweetened, and what that meant for their long-term risk of developing type 2 diabetes.

Participants filled out detailed food-frequency questionnaires, including how often they drank sugar-sweetened beverages (think regular cola, lemonade, and energy drinks), and artificially sweetened beverages like the “diet”, “zero”, or “no-sugar” versions.

Researchers grouped intake from “rarely or never” to “one or more a day,” and then observed who developed type 2 diabetes.

The surprising link between diet drinks and diabetes

It’s no secret that drinking sugar-sweetened beverages (whether sodas or energy drinks) is linked to obesity and metabolic disease. This new study confirmed that connection: people who consumed these sugary drinks daily had a 23% higher risk of developing type 2 diabetes compared to those who rarely drank them.

But here’s the twist: the study found that people who only drank diet sodas every day had an even higher risk. Up to 83% greater in some analyses.

Even after adjusting for things like body weight, waist size, smoking, and physical activity, the risk from diet drinks remained elevated. This suggests that the problem isn’t just that people who drink diet soda are already at higher risk for diabetes. Instead, it’s that these beverages may be contributing directly to that risk.

So… How can diet soda increase diabetes risk?

Researchers don’t have all the answers yet, but there are some clues. Some artificial sweeteners may affect the gut microbiome in ways that impair how our bodies handle sugar. Others might confuse the body’s natural insulin response, leading to blood sugar spikes even without real sugar being present. And there’s also the possibility that drinking diet sodas may lead people to overeat in other areas, thinking they’ve saved calories on their drinks.

In short, artificial sweeteners might not be as “neutral” as we once thought.

A wake-up call for the world

Australia, like many countries, has a growing diabetes problem. About 1 in 20 Australians has diabetes, most of it type 2. Many drink soft drinks regularly, and while public health efforts have focused on reducing sugary drink consumption (through campaigns and proposals for sugar taxes), there has been far less scrutiny of diet drinks.

This new study suggests that swapping a regular soda for a diet one may not be a free pass after all.

What should you drink instead?

Water, tea, coffee (without added sugar), and sparkling water are safer bets. If you need flavor, adding a splash of citrus or a few slices of cucumber can help. It’s also worth checking how often you reach for “diet” options out of habit, and whether you’re doing so in the belief that they’re harmless.

Bottom line

This study is one of the largest and most rigorous to date examining the long-term health impacts of sweetened beverages in Australia. Its findings challenge the assumption that diet drinks are a healthier alternative to sugary sodas—and call for public health policies to address both types of drinks.

So next time you're reaching for a can labeled "zero sugar," it might be worth asking: zero sugar, yes, but at what cost?

If you want to learn more, the original article titled "The association of sweetened beverage intake with risk of type 2 diabetes in an Australian population: A longitudinal study" is available on Diabetes & Metabolism at https://doi.org/10.1016/j.diabet.2025.101665.