Any studies done on potential health effects due to Ramadan will need to deal with the issue of noncompliance, i.e. to what degree do people observing Ramadan actually stick to the fast and not “cheat” at all. But I can imagine that due to the religious significance of the fast, you likely won’t get accurate self-reports of noncompliance. It would also be hard to conduct an accurate observational study since the subjects’ behavior will change due to being observed, again, because of the religious aspects. Without good noncompliance data, I’d be skeptical of any firm conclusions.