Weber gave us The Protestant Ethic and the Spirit of Capitalism and in so doing pointed out that religious Calvinism provided a knowledge structure, a life structure which its adherents were to follow. It included a belief that we are all fallen sinners, ascetic self denial, extremely (almost penitential) hard work, especially at your vocation, and tremendous devotion.
From this structure, some New England Protestants became very wealthy. Work hard, deny yourself, reinvest turns out to be a great way to make money. Around Ben Franklin's time, this cultural structure, this meme, jumped from a religious venue, to a capitalist one. And the Calvinist Work Ethic, became the American Capitalist Ethic. And it's still going strong.
American culture is sometimes called "puritanical" and it is true we can be weirdly prude sometimes. But in my mind, the proper use of "Puritanical" focuses more on that cultural structure developed by the Protestants and documented by Weber. Along with capitalism, this structure has become the skeleton for other knowledges/lifestyles as well.
Look at Environmentalism. It begins with a belief in a flawed humanity (everybody must use some resources), is driven by a penitential self-denial and ascetism (I won't enjoy air conditioning even if it's 95 degrees and humid out), shares a disgust in hedonism (a hummer and a 4000 sq ft McMansion are the problem), but also shares a belief that if we all work really hard together we can achieve salvation (Ecotopia). This working really hard includes paying more for hybrids, recycling, green products, basically everything.
So that environmentalism as a knowledge base and lifestyle has itself been hung on that structure provided by the Calvinists and the Capitalists.
But, the food and diet knowledge/lifestyles fit this structure as well. According to conventional wisdom people are fat because they are indulgent and lazy (gluttonous and slothful in Calvinist language). They eat rich foods and won't exercise. In order to improve, we/they need to practice self-denial and discipline by eating low fat, high fiber wholegrain (ascetic) foods while NOT eating fatty salty (indulgent) foods. We need to work extremely hard at exercise. The congregation is so fallen, that some improvement will be had with just 15 minutes of exercise (prayer) a couple times a week. But true results will come only with an hour or more of exercise almost daily. Talk about devotion.
The Anti-Pleasure Principle - Reason Magazine