It isn't clear to me if that study makes any attempt to control for confounding variables. Like, maybe people that are already obese or suffering from heart disease are more likely to consume sugar substitutes? I haven't had time to read the original study and ctrl+F did not locate the phrase "3rd variable" or "confound[ing|er]:" https://www.nature.com/articles/s41591-023-02223-9.epdf