But here we go, from his blog:
"If you go back and look at the instances where observational effects in nutritional studies have been tested by randomized, controlled trials, the track record is not good. In fact, it's so horrendous that the authors state baldly that 'There is now enough evidence to say what many have long thought: that any claim coming from an observational study is most likely to be wrong.'"Science has spoken: we can now stop paying attention to these nonsensical studies.
But do read the whole thing, as there is also a recommendation on how to fix it. I think it's unlikely to ever be fixed, however, as the real "product" of this process is employment for academics, not actionable science.
If they employed real process control and measurement, someone might figure out that the whole thing is a waste of time and money. And then those academics would be out of work.