This theory has actually been around for a while now - since at least 2005, unless I'm mistaken.
A few years ago, Mayo Clinic published similar findings:
Eating Lots of Carbs, Sugar May Raise Risk of Cognitive Impa [...] | Mayo Clinic News Network
Is it definitive? Of course not. You have to take these things with a healthy dose of skepticism. But, based on my own experience, I do believe there could very well be something to it.
For many, many years I ate lots of so called "complex carbohydrates." I rarely touched soda or fruit juices, and limited myself to brown rice, beans, homemade whole wheat bread, etc. I avoided fat, exercised regularly, and tried to do all the things that the medical community tells you is part of a healthy lifestyle. Yet, despite trying to do everything right, I gained an incredible amount of weight. At one point I was 120 pounds heavier than what I weighed after high school.
Ten years ago I became prediabetic. Last year, it had developed into full blown diabetes. Coincidentally, around this same time my wife told me she was becoming concerned because I was starting to develop cognitive problems. I would start to talk and in mid-sentence couldn't remember what I was talking about, or couldn't find words. Now many will say this is simply a part of growing older. But my problem came on so suddenly that it really scared me a little.
When I changed my diet to throttle back carb intake and increase fat, it was life changing. Even though I was consuming more calories than ever before (I currently eat around 2500 calories a day), 90 pounds of weight melted off. Like magic. My energy came back, my brain fog lifted, GERD went away, cholesterol normalized, and the diabetes has completely regressed. Two months ago, I had my annual physical and the doctor told me that he very rarely ever sees these types of health problems simply disappear.
Are carbs detrimental to everyone's health? Obviously, there are many people who seem to thrive on them. At the same time I also think we're not a one-diet-fits-all group of mammals. We've evolved to thrive on a varied diet, and there are also far too many variables involved for physicians to make generalized statements or prescribe the same diet for every single person. Some of us don't react well to carbohydrates - simple, complex, or otherwise. I happen to fit into that category.