Obesity in Developing Countries?

I'm doing some research on nutrition, child health and public programs in Mexico and, in the process of looking for a paper, came across this interesting article in JAMA about obesity among the Mexican poor. It turns out that obesity rates among the poor in Mexico rival those in the United States (obesity rates in general have followed a similar trend to the US, with large increases occurring between the 1980s and 1990s). This is especially interesting given that poor Mexicans live in conditions similar to the developing world, where obesity is only common among the upper strata of the population (though this is starting to change; exs: rural India and China). Doubly interesting is the growing phenomenon of young children who are both stunted and overweight, an interesting paradox of early life deprivation, on the one hand, and excess on the other.

Causes for the rapid increase in Mexican obesity are likely similar to those in the U.S.: changes in technology and policy that alter the balance between caloric input and output. For example, this paper notes that increasingly sedentary lifestyles and changes in diet are likely largely responsible for increased fattening. While I'm not sure if anyone has really stepped in and done some kind of accounting exercise or decomposition trying to explain time-trends in Mexican obesity, this doesn't seem to be a bad conjecture to make given the evidence.

We know from the United States that the poor are much more susceptible to these secular trends: healthy food appears to be a normal good, fast foods inferior, and exercise a luxury good. At least from what I can gather from the Mexican evidence, this is likely to be the case south of the border, as well. But are there reasons, external to basic economic theory, that might explain why the poor tend to be more obese?

There are some interesting biological theories that suggest that individuals who are deprived of nutrition while in the womb but exposed to relative abundance thereafter are more likely to become obese, diabetic, and develop cardiovascular disease. The idea is that fetus' adapt to scarcity, which results in permanent metabolic/endocrine changes. While these changes are advantageous in scarcity, the might actually be maladaptive in situations of relative abundance. Some evidence supporting this theory in (laboratory) animal and human populations can be found on pp 44-45 of this very thorough survey on the economics of health and socioeconomic status in developing countries (a must read for all interested in health and development as an area of research).

So tying this back to poverty: poor individuals are either more likely to be born in situations of deprivation or, in the case of economy wide shocks, unable to smooth their consumption so as to prevent under-investments in their kids during the fetal period and early childhood years. Faced with falling (unhealthy) food prices and secular changes in the level of human activity, if the biology behind the aforementioned theory is sound, these individuals might be doubly affected in terms of developing metabolic and cardiovascular conditions. Notice that the theory would also explain the stunted/overweight kids: stunting is a result of the fetal adaptation to scarcity, and overweight the result of exposure to abundance.

While some work on the Dutch and Chinese famines support this hypothesis (see the previous link), I am not aware of any other work looking the interaction between early life conditions/endowments and secular changes in technology. As a result, and since the marginal cost of adding this on as a project is low (I am using a well-suited Mexican dataset for another purpose, anyway), I've decided to have a go at the theory and see what I find. I'll keep you posted.