Studies suggesting diet sodas are worse than regular sodas may be misleading due to 'unhealthy user bias'.

“there's a non healthy user bias to a lot of these so the one of the more obvious examples other studies that suggest that diet sodas are you know worse for you than sodas but of course it misses a very obvious or clear thing that you know might be missing which is who are the patients who are going to disproportionately consume diet sodas you know certainly a subset of them might be people who are more health-conscious and say well if I want a soda I'd rather it be Diet than not but it's more often the people who are being told look you can't have a regular soda and so therefore you're selecting for less healthy patients