Does anyone think this is strange?

In every study regarding the benefits of diet, supplements and medicine on the healing process, there is never any consideration given to a mind-body connection. There is the underlying assumption that a person's thoughts, moods, temperaments, levels of stress,, etc have no effect on healing outcome of the drug or diet and are consequently not investigated as part of the study. I don't think there is a serious physician who doesn't consider stress to have an effect on the body and that meditation and an optimistic attitude to be important as well. Yet it seems to be completely ignored when it comes to double blind experiments. Look at any serious study such as one on statins, vegan diets, prozac, etc.. You have a control group and the group that takes the drug/diet and you have a statistical analysis of the results which is focused on the body's response independent of psychological variables. I'm not referring to the placebo effect and a particular belief regarding the efficacy of a drug or diet, but the general mood of the person. Does a guy who's angry at the world in general benefit equally from a drug/diet as one who is cheerful and optimistic? No one really knows since, to my knowledge, it isn't part of the variables that is looked at during these type of studies. In any event, it seems strange to me.