Denise Minger has just put up another great China Study post that's worth reading if you haven't already. Denise has been busy applying her statistics skills to the mountain of data the study collected. She noted in a previous post that wheat intake was strongly associated with coronary heart disease (CHD), the quintessential modern cardiovascular disease. I, and several other people, requested that she work her mathmagic to see if the association could be due to some other factor. For example, wheat is eaten mostly in the Northern regions of China, and CHD rates are generally higher at higher latitudes (vitamin D insufficiency?). This is true in Europe as well, and may be partly responsible for the purported benefits of the Mediterranean diet. You can mathematically determine if the association between wheat and CHD is simply due to the fact that wheat eaters live further North.
To make a long story short, nothing could explain the association except wheat itself, even latitude. Furthermore, she found a strong association between wheat intake and body mass index, typically a predictor of fat mass although we can't say that for sure. That finding echos a previous study in China where wheat eaters were more likely to be overweight than rice eaters (1, 2). Head over to Denise's post for the full story.
The China Study has major limitations built into its basic design, due to the fact that it was observational and pooled the blood samples of many individuals. Therefore, its findings can never prove anything, they can only suggest or be consistent with hypotheses. However, the study also has some unique advantages, such as a diversity of diets and regions, and the fact that people had presumably been eating a similar diet for a long time. I feel that Denise's efforts are really teasing out some useful information from the study that have been de-emphasized by other investigators.
There has been very little serious investigation into the health effects of wheat in the general population. Researchers studying celiac disease and other forms of gluten allergy, and the efforts of the paleolithic diet community in spreading that information (for example, Loren Cordain and Pedro Bastos), have been major contributors to understanding the health effects of wheat. Denise's analysis is one of the strongest pieces of evidence I've come by so far. I think there's enough indirect evidence that investigators should begin taking the idea seriously that wheat, particularly in the form of industrial flour products, may contribute to chronic disease in more than just a small subset of the population.