There has been a growing contingent of nutritionists (see here and here) who have been arguing that the increasing rates of obesity along with other ailments in America are not due to sugar or carb consumption or due to a lack of exercise but rather correlated with seed oil consumption.
The mechanism is particularly interesting. According to the previously linked Chris Kresser blog post, "Research in mice indicates that consuming high levels of linoleic acid, the primary fatty acid in industrial seed oils, alters neurotransmitter signaling, ultimately increasing food consumption and fat mass. (28) In mice, a diet high in soybean oil induces obesity, insulin resistance, diabetes, and fatty liver disease. (29, 30) Animal research also suggests that canola oil may cause insulin resistance. (31)"
Many nutritionists now also highlight how prevalent seed oils like corn oils, soy bean oils, sunflower oils and rapeseed oils are in the most common grocery store items in America.
what drove corn oil production up in America over the past two decades?