What does it mean to say that some diseases are specific to Western civilization, as Pollan does?

The statement specifically refers to the Western diet as a direct contributor to diseases such as cancer, diabetes, and heart disease. These diseases are said to be specific to Western civilization because populations with native diets are less susceptible to them.
In other words, if you adopt the Western diet, you are more likely to get diabetes, heart disease, and cancer. Why? Pollan maintains that the Western diet largely consists of refined grains (like white rice and pasta), large quantities of meat, and highly processed food (which contain high levels of fats, sugars, and preservatives). Absent from this diet are adequate quantities of whole grains, fruits, and vegetables (the kind of food that keeps these diseases at bay).
In the book, Pollan contrasts the Western diet with the Aboriginal diet in Western Australia. He catalogs how a group of overweight, diabetic Aborigines were able to temporarily reverse the progress of their "Western-style" diseases by eating native fare for seven weeks. Prior to the start of the experiment, the Aborigines subsisted on a typical Western-style diet: white flour products, refined grains, alcoholic drinks, carbonated beverages, potatoes, a huge quantity of cheap meat, and processed meals with high levels of sugar and fat. All showed symptoms of "metabolic syndrome," which has been implicated in a whole host of "Western-style" diseases.
Sufferers of "metabolic syndrome" typically consume a Western diet and enjoy a sedentary lifestyle.
During the experiment, the group of Aborigines had to hunt and gather their own food. Thus, they survived by hunting fresh fish, seafood, birds, kangaroos, crocodiles, and turtles. At other times, they gathered insect larvae, grubs, yams, figs, and bush honey. Basically, the group relied on native Aboriginal fare for their sustenance. At the end of the seven weeks, all of the Aborigines had lost weight and improved their blood pressure readings. Many also had normalized triglyceride levels and increased levels of omega-3 fatty acids in their tissues.
Most importantly, all of the Aborigines saw a decrease in type 2 diabetes metabolic abnormalities.
In sharing with us the results of the study, Pollan makes his point that some diseases are specific to Western civilization.