I found this quote concerning the general leanness of Asians on relatively carb-rich diets particularly interesting in light of my own conclusions:
The Asian question first. I do address this in the book and I address it again in the afterward of the paperback. There are several variables we have to consider with any diet/health interaction. Not just the fat content and carb content, but the refinement of the carbs, the fructose content (in HFCS and sucrose primarily) and how long they’ve had to adapt to the refined carbs and sugars in the diet. In the case of Japan, for instance, the bulk of the population consumed brown rice rather than white until only recently, say the last 50 years. White rice is labor intensive and if you’re poor, you’re eating the unrefined rice, at least until machine refining became widely available. The more important issue, though, is the fructose. China, Japan, Korea, until very recently consumed exceedingly little sugar (sucrose). In the 1960s, when Keys was doing the Seven Countries Study and blaming the absence of heart disease in the Japanese on low-fat diets, their sugar consumption, on average, was around 40 pounds a year, or what the Americans and British were eating a century earlier. In the China Study, which is often evoked as refutation of the carb/insulin hypothesis, the Chinese ate virtually no sugar. In fact, sugar consumption wasn’t even measured in the study because it was so low. The full report of the study runs to 800 pages and there are only a couple of mentions of sugar. If I remember correctly (I don’t have my files with me at the moment) it was a few pounds per year. The point is that when researchers look at traditional populations eating their traditional diets — whether in rural China, Japan, the Kitava study in the South Pacific, Africa, etc — and find relatively low levels of heart disease, obesity and diabetes compared to urban/westernized societies, they’re inevitably looking at populations that eat relatively little or no refined carbs and sugar compared to populations that eat a lot. Some of these traditional populations ate high-fat diets (the Inuit, plains Indians, pastoralists like the Masai, the Tokelauans); some ate relatively low-fat diets (agriculturalists like the Hunza, the Japanese, etc.), but the common denominator was the relative absence of sugar and/or refined carbs. So the simplest possible hypothesis to explain the health of these populations is that they don’t eat these particularly poor quality carbohydrates, not that they did or did not eat high fat diets. Now the fact that some of these populations do have relatively high carb diets suggests that it’s the sugar that is the fundamental problem. Ultimately we can only guess at causes using this kind of observational evidence. To know anything with certainty we’d need the kind of randomized controlled trials I yearn for in the epilogue of GCBC.
It has been some time that I have thought it's less to do with carbohydrate and more to do with grains (wheat, in particular), sugar, vegetable oils, and all the heavy processing and refinement that goes into those commodities, as well as the thousands of cheap derivative Frankenfoods derived therefrom.