10 potential reasons you're fat

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Writing in Slate, Sydney Spiesel points to this really interesting paper by Keith et al. in the International Journal of Obesity. The researchers propose 10 potential reasons for the rise of obesity in the US:
We do not review all plausible contributors to the epidemic but select those that are most interesting and for which the totality of current evidence is strongest. Figure 1 portrays the secular increase in a number of key indicators of these putative causal influences. For most Additional Explanations, we offer the conclusion that a factor (e.g., X) that has contributed to the epidemic will logically follow acceptance of two propositions: (1) X has a causal influence on human adiposity and (2) during the past several decades, the frequency distribution of X has changed such that the relative frequency of values of X leading to higher adiposity levels has increased. In the absence of countervailing forces, if both propositions are true, obesity levels will increase. Therefore, for postulated factors supported by this line of propositional argument (Additional Explanations 1-7), we evaluate evidence addressing whether the factor can increase fatness and whether the factor's frequency distribution has changed in the obesogenic direction. For the remaining Additional Explanations, propositional arguments vary in form and are outlined separately.

The 10 explanations are:

  1. sleep debt
  2. endocrine disruptors (industrial pollution)
  3. reduction in variability in ambient temperatature (air conditioning)
  4. decreased smoking
  5. pharmaceutical iatrogenesis
  6. changes in distribution of ethnicity and age
  7. increasing gravida age
  8. intrauterine and intergenerational effects
  9. greater BMI is associated with greater reproductive fitness yielidng selection for obesity-predisposing genotypes
  10. assortative mating and flor affects

And here's Figure 1:

Explanation 8 (intrauterine and intergenerational effects) is the most intriguing. The authors propose that extreme over and underfeeding in utero may contribute to later life obesity. There's some evidence that this effect can persist across generations, potentially creating a positive feedback loop.

As the authors admit, the evidence is basically correlative, but so is the evidence for the big two explanations (food marketing practice/technology and decreased physical activity). The key question is what the relative size of each effect is, but as the authors point out, we don't really know that yet.


I don't see how explanation #9 is varying over time, except in terms of explanation #10. Art De Vany had a nice paper describing a plausible reason for getting fat in terms of strategies for dealing with wildly varying food availability over time, and it doesn't take a Darwin to see that a predisposition to eat has usually been pro-survival, but why would this be contributing more to obesity now than 100 years ago?

Because food is more available due to increases in the standard of living? Haven't you ever heard your parents talk about how all they got for lunch when they were little was a plate of warm gravel?

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