Sarah Kliff writes
But more recent research, particularly a highly cited study in the American Journal of Clinical Nutrition, suggested that was more a question of genes than habits. The study, which followed 5,092 pairs of British twins ages 8 to 11, found that the most influence parents have on obesity is actually genetic, a factor of inheritance, rather than the environment. “Contrary to widespread assumptions about the influence of the family environment, living in the same home in childhood appears to confer little similarity in adult BMI [body mass index],” authors Jane Wardle, Susan Carnell, Claire Haworth and Robert Plomin write.
The research raises one key question: If obesity is genetic, why has it increased so much in recent years? The researchers explain that, some of the genetic predispositions for obesity have existed for awhile. But changes to our food environment, like the proliferation of fast food, have enabled those predispositions to become more powerful.
“Although contemporary environments have made today’s children fatter than were children 20 years ago, the primary explanation for variations within the population, then and now, is genetic differences between individual children,” they write.
One thing, just as a comment on how public health is done in America, is that “everyone” knows this.
That is to say, its nearly impossible to spend more than 6 hours on Google Scholar researching obesity and not come away knowing that obesity is high heritable. You might question whether the heritability has declined over time, but looking this up will point you to immediately to studies which suggest, no.
You’ll hear offhanded references to this fact when you read certain obesity researchers who write phrases like: “whatever is happening is happening to us all”
However, few people come out and say it. The fear I think is that if people believe that obesity is genetic they will stop trying to do anything about it. The problem is that the implicit lying to people causes all types of immediate human suffering.
Those who have been reading me for a while know that this is also the case with exercise. Its well known that exercise as an intervention is unlikely to cause a reduction in body fat percentage. Yet, this fact is shoved under the rug seemingly because exercise has extensive health benefits and the public health authorities know that lots of people would stop exercising if they were aware it was unlikely to cause them to loose weight.
On many counts the way public health is treated in America borders on intentional deception.
Secondly, no one knows for sure why obesity has exploded. Indeed, though I doubt this is the answer, I have not seen anyone convincingly show that it is not genetic.
That is, that it is not assortative mating. Under this theory fat genes are synergistic. If you have fat gene 1 you are 20 lbs overweight. If you have fat gene 2 you are 10 lbs overweight. If you have fat genes 1 and 2 you are 50 lbs overweight.
When overweight people marry overweight people they then have morbidly obese children. This would help explain the bimodality of obesity but off the cuff you would expect the thin peak to expand not contract, if this was the case.
Still, differential reproduction rates might get you around this.
In any case I don’t think that’s the likely answer, but the point is that no one actually knows for sure what the answer is and whatever it is it has to amenable to the fact that not only is obesity highly heritable but its heritability has not changed – up or down – since the onset of the epidemic.