Artificially sweetened “diet” sodas have long been touted as a safer alternative to sugary drinks, especially for people watching their weight or blood sugar. In fact, UK health advice notes that approved low or no-calorie sweeteners are considered safe substitutes for sugar and can help reduce sugar intake.

However, emerging research suggests a surprising link: frequent consumption of diet soft drinks may actually increase the risk of developing type 2 diabetes. A major Australian study found that adults who drank one can of diet soda a day had a 38% higher risk of developing type 2 diabetes compared to non-drinkers, even higher than the 23% increased risk seen in those who drank sugary sodas daily.

This blog unpacks the evidence behind this counterintuitive finding, explains possible reasons, and offers practical guidance.

The sweetener vs. sugar assumptions

Most people know that sugar-sweetened beverages (SSBs) like regular cola, lemonade and energy drinks are linked to weight gain and diabetes. Indeed, meta-analyses show that people with high intake of sugar-sweetened drinks have roughly a 30% higher risk of developing type 2 diabetes.

Health guidelines worldwide (including UK NHS advice) urge us to cut down on added sugars for this reason. Diet drinks, sweetened instead with artificial sweeteners (like aspartame, sucralose, acesulfame-K, etc.), were introduced on the assumption that they avoid the blood sugar and calorie load of sugar.

Short-term trials find that when people replace a sugary drink with a diet version, they often eat fewer calories and may lose weight, and there’s no clear evidence that sweeteners increase appetite.

On this basis, diabetes guidelines often suggest diet drinks are a better choice than regular soda. For example, one recent survey of people with diabetes noted that switching sugar drinks to diet sodas was associated with lower risk of death and cardiovascular disease.

However, in contrast to these beliefs, growing evidence from long-term studies is painting a more complex picture. The World Health Organization after reviewing the literature, even advises against using artificial sweeteners for weight control, stating there is no long-term benefit and possible harms, including an increased risk of type 2 diabetes.

In practice, many people in Australia, the UK and elsewhere do rely on diet soft drinks for a sweet fix. In the EU, for instance, diet soda consumption rose from 23% of people in 2016 to 30% in 2021. It’s therefore important to understand whether these sugar-free options are as harmless as once thought.

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New Australian research: diet sodas and diabetes risk

A high-profile Australian cohort study (led by Monash University and published in Diabetes & Metabolism) suggests the risk of diabetes may be higher with diet drinks than with sugary ones.

Researchers followed 36,608 Australian adults (aged 40–69) for nearly 14 years. Participants self-reported how often they consumed sugar-sweetened or artificially sweetened beverages. After accounting for diet, exercise, education and health history, they found:

• Diet soda drinkers (≥1 can per day) were 38% more likely to develop type 2 diabetes than non-drinkers of sweetened beverages.
• Sugar soda drinkers (≥1 can per day) had a 23% higher risk.

In other words, daily diet drinks appeared even more strongly associated with diabetes than daily sugared drinks.

These findings have attracted media attention worldwide. A recent press report summarised: “drinking just a single can of artificially sweetened soft drink a day… was associated with a 38 percent higher risk of developing type 2 diabetes”.

It pointed out that this was based on detailed records of 36,608 Australians over 14 years, and that this risk exceeded the 23% increase linked to sugar drinks.

Key takeaway: The Australian data suggest that long-term daily consumption of diet soft drinks may notably increase the risk of future type 2 diabetes.

This is a surprising result, because it runs counter to the idea that cutting sugar from your drinks automatically makes them “safe”. Importantly, these are associations observed in a study, not proof of direct causation, but the strength of the link, especially after statistical adjustment, raises concerns.

Evidence from other studies

The Australian study is not an isolated case. Other large observational studies have reported similar associations between diet drinks and diabetes or metabolic disorders:

• United States (MESA study, 2009): The Multi-Ethnic Study of Atherosclerosis followed middle-aged adults free of diabetes. It found that daily diet soda drinkers had a 67% higher risk of developing type 2 diabetes over time, compared to those who did not drink diet soda.

This was true even after adjusting for body weight and other risk factors (though diet soda’s link to metabolic syndrome components was partly mediated by weight gain).

• France (NutriNet-Santé cohort, 2023): A web-based study of 105,588 participants tracked diet and health outcomes. Individuals consuming higher amounts of artificial sweeteners had significantly higher diabetes risk: for example, those above the median intake had a 69% greater risk (hazard ratio ~1.69) of developing type 2 diabetes versus non-consumers. This held after accounting for many lifestyle factors and changes in weight.
• Other cohorts: Several European and US cohorts have reported positive associations between diet beverages and type 2 diabetes risk, although results vary. Some analyses suggest the risk is attenuated or disappears after adjusting for obesity, while others (like the Australian and French studies) find it persists.

Systematic reviews of such cohort studies tend to show a small but significant positive association between artificial sweetener intake and diabetes risk, although confidence is often graded as low due to study limitations.

These human studies cannot prove that diet sodas cause diabetes. It is possible, for example, that people predisposed to diabetes (e.g. already overweight) are more likely to switch to diet drinks, which could confound the findings (“reverse causality”).

That said, investigators in the Aussie study explicitly adjusted for body mass index and found the diet-drink link remained significant, suggesting it was not solely due to obesity. Similarly, the US MESA study found the diabetes risk from diet soda was independent of baseline weight or weight change.

Notably, some studies report that when you do adjust for weight, the effect for sugary drinks disappears but the effect for diet drinks does not. One news summary observed: “when body weight was factored in, the link between sugary drinks and type 2 diabetes disappeared – suggesting being overweight was driving that association.

[But] when body weight was factored into the artificial sweetener link, the increased risk was still present”. This pattern hints that diet drinks may influence glucose metabolism or diabetes risk through mechanisms other than simply promoting obesity.

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Possible biological mechanisms

How might “zero-calorie” sweeteners raise diabetes risk? Scientists have several hypotheses, though the exact pathways remain unclear:

• Insulin response: Some research suggests certain artificial sweeteners (notably aspartame) can trigger an insulin response similar to sugar, despite having no calories. Insulin spikes can affect blood sugar control and insulin sensitivity over time.
• Gut microbiota changes: Laboratory studies have found that sweeteners like saccharin or sucralose can alter the composition of gut bacteria. This dysbiosis has been linked to increased glucose intolerance and may contribute to metabolic disturbances.
• Sweet taste confusion: Chronic exposure to very sweet tastes without calories might “confuse” the body’s regulatory systems, possibly affecting appetite hormones or energy balance. (However, human studies have not consistently shown that sweeteners make you hungrier).
• Reward pathways: Some theories propose that artificially sweet beverages maintain a preference for sweet foods, which could indirectly influence diet quality, but evidence is mixed.
• Other metabolic effects: There may be unrecognised metabolic effects of food additives or interactions with other aspects of diet.

In short, the biological reasons for the observed link are not fully established. As ScienceAlert noted, “so many known contributors to type 2 diabetes” exist that researchers cannot yet say artificial sweeteners directly cause diabetes.

Indeed, a recent comprehensive review concluded that randomised trials and most systematic reviews have not provided definitive evidence that non-nutritive sweeteners raise diabetes risk.

This ambiguity led WHO to issue a conditional guideline: while the evidence suggests potential harms (like higher diabetes risk), it may be confounded by other factors. WHO therefore recommends reducing sweetener use as a precaution.

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What health authorities say

Health agencies and expert bodies take a cautious stance:

• The World Health Organization (WHO) (May 2023) explicitly advised against using non-sugar sweeteners for weight control or to prevent disease. Its guideline found no long-term benefit of sweeteners and noted potential “undesirable effects such as an increased risk of type 2 diabetes, cardiovascular diseases, and mortality”.

WHO warns this may be due to confounding (“link may be complicated”), but nonetheless suggests that people should aim to reduce sweet tastes altogether.

• In the UK, the NHS states that approved sweeteners are safe alternatives to sugar. It notes that swapping sugary drinks for no-calorie drinks can help reduce calories and tooth decay. The NHS also acknowledges that short-term trials find weight benefits with sweeteners, but that long-term observational studies are conflicting and limited. Diabetes UK similarly points out that artificial sweeteners can reduce carbohydrate intake but advises using them instead of sugar, not in addition.
  
  
• Australian experts highlight the new findings. For example, Professor de Courten (RMIT/Monash) said the study “challenges the assumption that artificially sweetened beverages are a safer choice”. Her team urges policymakers to extend measures like sugar taxes to diet drinks too. She remarked: “We support measures like sugary drink taxes, but our study shows we also need to pay attention to artificially sweetened options… These are often marketed as better for you, yet may carry their own risks”.

In summary, while no health agency has banned diet sodas, there is growing caution. WHO’s advice highlights that “non-sugar sweeteners are not essential dietary factors and have no nutritional value” and that their long-term use could be harmful. The consensus message is moderation.

Swapping to water and healthy alternatives

Given this uncertainty, experts now encourage people (especially those at risk of diabetes) to favour water and unsweetened drinks whenever possible. In fact, a recent clinical study presented at the American Diabetes Association meeting found that switching from diet soda to water dramatically improved outcomes for women with type 2 diabetes.

In that trial, 81 overweight/obese diabetic women were randomly assigned to replace their usual post-lunch diet soda with water (while all participants followed a weight-loss program). At 18 months, the water group lost significantly more weight and – most strikingly – 90% of them achieved diabetes remission, compared to only 45% of the diet-soda group.

This underscores the practical point: water is the healthiest drink choice. We embed an image below illustrating this principle.

Even if you enjoy sweet drinks, consider unsweetened options first (sparkling water with lemon, plain tea/coffee, etc.). If you do use artificial sweeteners, use them sparingly. 

For diabetic individuals, the take-home is similar: one diet soft drink a day may not be harmless. It’s wise to monitor blood glucose closely and discuss drink choices with your healthcare team. Drinking plenty of water and cutting back on all sweetened beverages (sugar-free or not) is a safe strategy.

Practical tips

• Read labels carefully: Many “diet” drinks contain potent sweeteners (aspartame, sucralose, etc.) but zero sugar. They may taste tempting, but remember the emerging risks.
• Limit frequency: If you do drink diet sodas, keep it occasional (not daily). Treat them like a rare indulgence rather than a daily habit.
• Hydrate with water: Aim for water as your primary drink. Carry a water bottle, flavour plain water with fruit or herbs, or have unsweetened tea/coffee instead of sweet soda.
• Mind overall diet: Focus on whole foods (vegetables, fruits, whole grains, lean proteins). Reducing ultra-processed foods (including sodas, diet or regular) is key to lowering diabetes risk.
• Lifestyle matters: Maintain a healthy weight and stay active. Even if you drink diet sodas, weight control and exercise remain powerful tools against diabetes.

How Vively can help you take control

Cutting back on diet sodas is a positive step, but it’s just one part of managing blood sugar and long-term health. Vively gives you the tools to see the bigger picture of how your daily choices affect your metabolism.

With Vively you can:

• Track your glucose in real time with continuous glucose monitoring (CGM), so you can see exactly how different drinks and foods impact your blood sugar.
• Understand your Wellness Score/Metabolic Health Score, which shows how your diet, activity, sleep, and stress are influencing your long-term health risk.
• Spot hidden patterns — for example, whether your “zero-calorie” drinks are linked to glucose fluctuations or cravings that affect your eating habits.
• Make confident swaps by reviewing your meal and drink scores, helping you choose water, unsweetened drinks, or foods that support stable energy.
• Stay motivated with progress tracking, bringing together your glucose data, habits, and improvements in one simple place.

By combining real-time insights from CGM with your personalised Wellness Score, Vively helps you move beyond assumptions about “healthy” alternatives and truly understand what works for your body.

“Many people assume that switching to diet soft drinks is a safe option, but the research shows it may not be that simple. At Vively, we help people move beyond the labels and see how their choices actually affect their body in real time. Our Wellness Score and CGM insights make it easier to spot patterns and build healthier habits that truly support long-term health.” — Charlotte Battle, Accredited Practising Dietitian & Lead Dietitian at Vively

Conclusion

In summary, while diet soft drinks were designed as a lower-risk alternative to sugary sodas, recent research suggests they are not risk-free. Large cohort studies from Australia, Europe and the US consistently report that habitual diet soda consumption is associated with a higher likelihood of developing type 2 diabetes.

The reasons are still under investigation, and causation has not been proven. Nevertheless, the finding is “surprising” to many health professionals. In light of this, health authorities advise caution: the WHO explicitly warns of potential harms (including raised diabetes risk) from long-term sweetener use, and leading experts now encourage water as the primary beverage for those at risk of diabetes.

For the general public and especially people with diabetes, the smart approach is moderation and awareness. Don’t assume “zero calories” means “zero consequences.” Limiting both sugary drinks and diet sodas, and choosing water or unsweetened beverages, is the safest bet for blood sugar control and overall health.