That's funny, I just recommended Walter Willett's book "Eat Drink and be Healthy" in another thread! Good article, but would have been better coming from someone with at least some medical background. I think this article and the Atkins diet boil down to the basic idea that not all fats are bad and controlling caloric intake and eating a balanced diet (read: not tons of carbs) is key to being healthy.
Despite what the article says, I think lifestyle changes have a lot to do with people's current health situation. He's big on noting the 80's as a major turning point. What happened in the 80's: cable television, video games and computers started to become mainstream and have been increasing their penetration into people's lives ever since: they didn't just break on the scene and remain unchanged in use.
Along with all of this sedentary lifestyle change is an increase in eating more as something to do rather than something people do because they're hungry. It's not always about hunger and satiation. I used to eat all the time, not because I was hungry, but just because I was bored or wanted to eat or drink something while playing games or watching TV for hours.
The author cites the position of low-fat, high cholesterol diet recommendations as the fault for obesity, but I don't think that can be the only cause or even a major cause. The rampant success of fast food restaurants, and microwavable meals are a testament to how much people abide by such recommendations. If the majority of people are not following those recommendations, how can they be the cause of the majority of people being obese?