How can nutritional science be made more accurate?

[ronaldemail1]

On the subject of diet. There is a lot of studies. But there is no pictures of the before and after of a person to sustain those studies.
(I am not taking about the marketing campaigns promoting diet). I just would like to see plain before and after pictures with real
people for every proposed diet. And then a follow up. Why it is so hard ? Maybe they all know that their proposition do not pass
a reality test.