"It is very hard to do a double blind study on diet because there is no placebo broccoli. You either know if you are eating it or you don't. And if you take it out of the diet to see what effect it does, you don't know if the perceived affect is a result of the subtraction or the addition of whatever you have put in it's place. So it's not like studying drugs." (1)
--Michael Pollan: Food Rules for Healthy People and Planet
Below, hear Michael Pollan speaking about why processed food and supplements are not the answer and why nutrition is such a hard thing to study.
In general, I agree with Pollan that processed food which is engineered to be healthy is the completely wrong direction to go if you are trying to eat healthy food. I also agree that blindly taking supplements to fix health problems is not the answer because individuals are so complicated and supplementation is even more complicated. But, individuals can benefit from supplementation provided it is done on an individual basis--and not in a large group study where one supplement is taking blindly without regard to their individual vitamin status.