That such a diet makes people sick and fat we have known for a long time. Early in the twentieth century, an intrepid group of doctors and medical workers stationed overseas observed that wherever in the world people gave up their traditional way of eating and adopted the Western diet, there soon followed a predictable series of Western diseases, including obesity, diabetes, cardiovascular diseases, and cancer. They called these the Western diseases and, though the precise causal mechanisms were (and remain) uncertain, these observers had no doubt these chronic diseases shared a common etiology: the Western diet.
Michael Pollan, In Defense of Food