Depending on whom you listen to, diet soft drinks are either nutritional science’s greatest achievement or its most magnificent Trojan horse – a deliciously sugar-free indulgence or a wolf in calorie-free clothing, set to ruin your health in other ways. Yes, you can drink them without adding much to your energy intake, but are you playing tricks on your appetite or insulin levels that might backfire? Is whatever has taken the place of all that sugar worse? It makes most sense to start with insulin. In case you are unfamiliar, this is a hormone, usually produced in the pancreas, that helps your body to use sugar for energy. It has been theorised for a while that your body has just as much trouble distinguishing between regular and diet soft drinks as your tastebuds, leading to overproduction of insulin that could cause everything from increased blood pressure to diabetes or stroke. Similarly, there are suggestions that artificial sweeteners in diet sodas can fool our stupid, sugar-loving brains into thinking that we have taken in more calories than we have, leaving our hunger hormones off-kilter. However, it looks as if these potential concerns may not be as much of a problem as nutritionists once thought, with a systematic review of studies published last year finding that exposure to sweeteners “did not conclusively induce increased food intake or change in subjective appetite ratings [and that] no significant change was seen in blood glucose levels, post‑prandial glycemic or insulin response after consumption”. Also, you may have heard that the International Agency for Research on Cancer (IARC) last year classified aspartame, one of the more common artificial sweeteners, as “possibly carcinogenic to humans”. This sounds bad, but it doesn’t mean a lot – only that a carcinogenic effect can’t be ruled out. It puts the sweetener in the same category as aloe vera extract and certain pickled vegetables. Drinking hot drinks, which we have covered before and working night shifts have a higher IARC risk rating. Good news for the diet drink lobby, then. But hold on: at least one observational study that looked at people’s habits over an eight‑year period found that drinking more than 21 artificially sweetened drinks a week almost doubled their risk of becoming overweight or obese. So what else could be going on? One answer may be that diet soda drinkers are more likely to be doing something that increases their obesity risk, such as regularly eating processed food or overeating because they believe they are “saving” on the calories they drink. Another may be that something else is happening. “Sucralose, which is often found in diet drinks, is thought to be one of the most common causes of bloating in the body,” says the nutritionist Lisa Richards. “But there’s also some evidence that it can cause gastrointestinal irritation and affect the bacteria that promote good overall gut health.” One study published last year suggested that sucralose consumption within the daily intake levels usually regarded as acceptable in humans can disrupt the gut microbiome and may also affect intestinal tissue. Another study, published in 2022, suggested that other sweeteners may have similar effects. More research is needed – much of the existing research has been done on mice – but this is probably the most worrying aspect of regular soft drink consumption, as an unhealthy microbiome can lead to a range of worse effects. So, how much should you worry? Well, if you are drinking diet drinks instead of water, multiple times a day, it is probably a good idea to cut back: whatever the mechanism, it could be making you unhealthy. If you are indulging less frequently, it may be less of a concern, but it is still worth experimenting with other drinks that could fill the gap without the potential negative effects. A quick squeeze of lemon in a glass of sparkling water may in fact help to keep your insulin levels in check – and it is also pretty tasty. It is a bit less portable than a can, but you can’t have everything.