Artificial sweeteners cannot be shown to be harmless with chronic use: large cohort studies link high intake to a higher risk of cancer, cardiovascular disease and cognitive decline, and laboratory research points to disruption of the gut microbiome. Yet causal evidence in humans is limited, and potential benefits for weight and blood sugar in diabetes are real. Moderate and mindful use seems wiser than consistently high daily use.
Diet sodas and products containing sweeteners are often seen as a healthy alternative to sugar. The picture emerging from recent research is, however, nuanced and sometimes contradictory. There are both possible benefits and concerns, and for many risks conclusive causal evidence is still lacking.
On the positive side: long-term use of non-nutritive sweeteners (NNS, the sweeteners found in diet products) appears to be beneficial for body weight and blood sugar regulation in people with type 2 diabetes, and is better for dental health than regular sugar (PMID 39339762). Some meta-analyses in humans also find no measurable negative effect on body weight or blood sugar in the general population (PMID 36364710).
At the same time, there are several concerns. A large French cohort study involving nearly 103,000 participants linked above-average intake of artificial sweeteners to a 13% higher risk of cancer overall. Aspartame was specifically linked to a 15% higher overall cancer risk and a 22% higher breast cancer risk; acesulfame-K was linked to a 13% higher cancer risk (PMID 35324894). The researchers themselves caution that selection bias and confounding factors cannot be fully ruled out, but the study is large enough to take seriously.
An important mechanism involves gut bacteria. Research from the Weizmann Institute showed that saccharin, sucralose and aspartame can cause glucose intolerance by disrupting the composition of the gut microbiome. This effect was transferable via fecal transplantation to mice without their own gut bacteria, which makes a causal relationship plausible (PMID 25231862). A smaller randomised study in 17 healthy adults found no effect on the gut microbiome at realistic doses after 14 days (PMID 33171964), suggesting that dose size and duration of use matter. Furthermore, one author of that latter study received a honorarium from PepsiCo, which limits its independence.
In addition, observational studies link high sweetener intake to cardiovascular disease, higher all-cause mortality, depression in adults and childhood obesity (PMID 38423749, PMID 36364710, PMID 37115819). In a prospective 8-year study of more than 12,000 Brazilians, higher consumption of low- and no-calorie sweeteners (including sugar alcohols such as erythritol and xylitol) was linked to faster cognitive decline, particularly in people under 60 years of age (PMID 40902134). Here too the findings are associations, and confounding factors have not been fully excluded.
The core of the problem is that almost all of the evidence is observational: people who consume large amounts of diet products differ in numerous other ways from people who do not. Causal evidence in humans is scarce. Nevertheless, the signals from multiple large studies are consistent enough to justify caution, particularly with chronic and high use. For occasional or moderate use, the risks are far less clear.
Ten studies used: large cohort studies (up to 102,865 participants), a prospective study over 8 years, an RCT (n=17), animal and human experiments (Weizmann), review articles and meta-analyses. Almost all evidence is associative; one study has a potential conflict of interest (PepsiCo honorarium). Total estimated number of participants (across the clinical studies): over 130,000.