It was the fad diet for something like 30 years. It lost ground, and I think he's pretty extreme with some of the garbage he has people eat, and goes overboard on limiting good carbs. He was also pretty arrogant, and didn't win over many skeptics by dismissing critics as "idiots" (I believe that was a word he applied to the ADA, who he said wouldn't figure out nutrition before his English Sheepdog did).

On the other hand I do think there's some merit to the argument that we should pay a lot more attention to the glycemic index, and nix, or at least limit foods (like highly processed carbs, and refined sugar) that cause the yoyo effect to your insulin levels.

He may have helped some people lose weight, and solve specific, weight related health problems, but he ignored the fact that, even if you're okay with killing animals for food, the way it's typically done for most of the meat production in industrialized nations is extremely unhealthy, inhumane, and environmentally disasterous.

If the factory meat industry wasn't so heavily subsidized, and had to clean up their effects on the environment, far less meat would be consumed, as the production would go down, they'd have to shoulder the burdens of doing business that are currently imposed on the government, the environment, and people's bodies, and prices would shoot through the roof.

In terms of feeding the world, the land use alone is ridiculous, not to mention the oil, the massive doses of hormones and antibiotics, etc, that feedlots require. Without even getting into frankenfoods, it's hard to see how a doctor could be so blind as to ignore the obvious concerns over such matters.