"I think this idea that the dietary advice of 20-30 years ago (low fat) is the primary cause of the obesity epidemic is the result of a desire for a dramaticall

"I think this idea that the dietary advice of 20-30 years ago (low fat) is the primary cause of the obesity epidemic is the result of a desire for a dramatically satisfying narrative." Again, you're arguing against a claim that isn't being made. The anti-carb claim is that the primary cause of the obesity epidemic is the vast consumption of sugars and other simple, processed carbohydrates. A contributing factor to this dietary problem is that even people who try to eat well have been led to believe that cutting out steak and replacing it with whole wheat bread would help them, which is wrong and was backed up by bad science. If you are having trouble believing that people think that the obesity problem is caused by nutritionists telling everyone to drink six Cokes a day, that is because nobody is claiming that. They are claiming that the problem which already existed was exacerbated by bad advice, and that lots of people who tried hard to do something about their own personal problems were frustrated and gave up because they were told to do counterproductive things.