I'm not sure I follow the point on open heart surgeries. What would the study be? Is there some question of fact that needs to be resolved? There are many kinds

I'm not sure I follow the point on open heart surgeries. What would the study be? Is there some question of fact that needs to be resolved? There are many kinds of open heart surgery too. Which one do you purport does not have any randomized trials associated with it? All of them? That would actually surprise me a little. Placebo-controlled RCTs are only feasible when it's possible to ethically apply the placebo or the treatment. Generally speaking, the types of things we do open heart surgery for, like valve replacement, coronary bypass, or pacemakers, it is impossible to ethically apply a placebo. You only need RCTs when there is some question of fact that needs to be resolved. There is no need for a random controlled trial about whether stopping all water intake will kill someone. For some types of heart surgery, this doubt does exist, but for any of those types which are not being studied with RCTs, I would guess there is not much doubt. If your heart valve is busted and it is causing you to be unable to pump blood, you can look at the pumping efficiency before and after replacement. No RCT needed. You'll note that these two factors are very different from diet. It is possible to ethically apply a control and a treatment where it comes to diet, and there is much doubt as to their efficiency for some purposes.