A section of a graph published by the New York Times on Jan 14 2009. It shows that the number of obese people in the USA has stopped growing. Peak fat?
Peaking of anything is always interesting for "peakers", people who study peak oil and the peaking of natural resources. So, is peak fat something that we can interpret as part of a general peaking phenomenon? In some ways, yes.
The interpretation given in the article is that peak fat is the result of some kind of physical limit: people can't just get fatter than they are already. It may be, but it is also true that we are not speaking of people getting fatter, but of the fraction of people who reaches values of the "body mass index" (BMI) that define obesity. So, if about 35% of adult males in the US are defined today as obese, there is no obvious physical limit that would prevent this number from going higher. Why not 50%? Or 75%?
What is the limit of obesity? It depends on what causes it. Obesity is sometimes taken as an indication of national wealth. The United States, it is said, is a rich country and there are so many obese Americans because they can afford to eat what they want. That is not the case; actually it is the opposite. In the United States, people get fat because they cannot afford to eat what they want.
There have been several studies (see, e.g., this link ) showing that poor people tend to optimize their diet in terms of the ratio of calories to dollars. In other words, they try to buy the cheapest food that can provide them with the same number of calories. Unfortunately, it turns out that this cheap food is what we call "junk food"; food rich in saturated fats and sugar. This is the kind of food that makes you obese. Healthy food is expensive in terms of calories per dollar and the poor cannot afford it. Surely, there are also cultural factors that lead Americans to eat junk food. But economic factors must play a major role.
So, I can propose an explanation for the peaking of the growth of obesity. It may be that poor people in the USA are becoming so poor that they can't afford any more even a diet of junk food. They must cut on the overall food budget and that is surely a way of losing weight, although not a planned one.
Of course, this is just a hypothesis but, if it is true, then "peak fat" is indeed related to the economy and - indirectly - to crude oil. The obesity epidemics started in the 1970s, when the US economy underwent what was termed "the great u-turn" by Bluestone and Harrison, who published a book with that title in 1982. The great u-turn led to an increase in the income inequality in the US, which is lasting to this day. In other words, the poor started becoming poorer and their diet started to worsen. The trend is continuing and, at this point, it may be that we have reached a turning point that makes even junk food unaffordable for the poor. In general, these economic trends are due in large part to the diminishing availability of mineral resources - oil is just one of them. So, peak fat may well be another effect of peak oil.