It is a mix of politics and economics and ethics and a very small probability of doing any real experimentation on other people.
So far I have more faith in Internet communities doing self-experimentation than with big corporation-sponsored studies.
Nutrition isn't some old-guard field with a hundred years of solid decided science weighing it down. In my opinion it's like genetics, a fast moving, exciting field full of interesting ideas and disruptive possibility.
Quite frankly, our understanding of the human GI and human nutrition is still rather pathetic, and a lot of the "common wisdom" is based on misinformation and bad evidence.
Anna Karenina, Part Two, chapter 19:
"He had no need to be strict with himself, as he had very quickly been brought down to the required light weight; but still he had to avoid gaining flesh, and so he eschewed farinaceous and sweet dishes."
This actually is a hard problem and the science well short of consensus. The surface area of the problem seems to grow every year as scientists publish new research. That seems like a good indication that the odds of this (relatively) uninformed approach being a great one is low.