Evidence suggests that diet soda is not a healthy choice and may have negative health effects, though it is not definitively proven to cause serious diseases like cancer.
Diet Soda is bad for you

Is diet soda bad for you? - Ohio State Health & Discovery
Source: health.osu.edu
Key Evidence
Ohio State Health & Discovery and University Hospitals warn about potential harms from artificial sweeteners and additives in diet soda.
health.osu.eduhealth.osu.eduIs diet soda bad for you?
uhhospitals.orguhhospitals.orgIs Diet Soda a Healthy Choice?
UCLA Health and Blue Cross Blue Shield cite observational studies linking diet soda consumption with stroke, weight gain, and metabolic dysfunction.
connect.bcbsmt.comconnect.bcbsmt.comDiet Drinks Are Soda-licious, But Come With a Price
uclahealth.orguclahealth.orgObservational studies shed light on diet soda consumption
MD Anderson Cancer Center states artificial sweeteners have not been proven to cause cancer.
mdanderson.orgmdanderson.orgDiet soda and cancer risk: What you should know
Examine.com notes diet soda may lead to overconsumption and metabolic issues.
examine.comexamine.comIs diet soda bad for you?
What the Evidence Shows
Multiple reputable health organizations and medical centers indicate that while diet soda does not contain sugar, the artificial sweeteners and chemical additives it contains may have harmful effects on health. For example, sources from Ohio State Health & Discovery and University Hospitals highlight concerns about artificial sweeteners and other additives potentially contributing to negative health outcomes. Observational studies cited by UCLA Health and Blue Cross Blue Shield of Montana link regular consumption of diet soda to risks such as weight gain, metabolic dysfunction, stroke, and other health issues. However, the MD Anderson Cancer Center clarifies that artificial sweeteners in diet sodas have not been proven to cause cancer, indicating no direct causal link to cancer risk. There is also discussion about diet soda potentially leading to overconsumption of calories indirectly by affecting appetite or metabolism (Examine.com). The Mayo Clinic notes that diet soda may help reduce calorie intake compared to regular soda but suggests there are healthier low-calorie alternatives. A Reddit discussion reflects skepticism about the relevance of some animal studies to typical human consumption levels, indicating some debate in public discourse.
In summary, while diet soda is generally considered less harmful than sugary sodas in terms of calorie content, evidence from observational studies and expert opinions suggests it is not a healthy beverage choice and may contribute to adverse health effects over time. There is no conclusive evidence that diet soda causes cancer, but its overall impact on metabolic health and disease risk warrants caution.