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muzukashidesuyo t1_ja30apj wrote

Are you suggesting obesity is just genetics? If so, why have obesity rates skyrocketed since the 90s/early 00s?


KuriousKhemicals t1_ja3792f wrote

What heritability actually shows is percent of variance is accounted for by genetics/inborn factors. How much variance there is can be environmental - that is, environment that is shared among all individuals in the study population, not just family environment. E.g. if weight was 100% heritable then genetic profile A would be 20th percentile and genetic profile B would be 90th percentile no matter what, but in 1920 that might have meant 110 pounds and 200 pounds, whereas today it might mean 130 pounds and 500 pounds. The actual weight of an individual still cannot be determined only by genetics.

Height is a good example to understand the counterintuitive math of heritability: it has become much more heritable over time because it's much more rare for people to experience malnutrition that impedes them from reaching their maximum genetic potential. The genetic pool hasn't changed significantly, and it has become more "genetically determined," but the increase in average height or the increase of height in subsequent generations of a family is very much due to environment.


muzukashidesuyo t1_ja3b495 wrote

Yes, basically genetics loads the gun, environment pulls the trigger. But the comment I responded to made it sound like genetics was the determining factor.


SerialStateLineXer t1_ja6vkwg wrote

What the other commenter said. Environment has made recent generations fatter than older generations, and makes people in rich countries fatter than people in poor countries, but in wealthy countries, within the current generation, genetics explains most of the variance in obesity, while upbringing explains very little.

This paper is based on a sample in Macao, and I don't know of any twin studies that were conducted in Macao specifically, so it's possible that they've found a causal factor that's peculiar to Macao or other wealthy East Asian countries. But we should be skeptical of this as a general causal explanation for obesity, given that it's contradicted by twin studies.

Edit: Note that the heritability of obesity doesn't mean that different people with the same lifestyle end up with wildly different BMIs because of genetics. Behavioral traits are also strongly heritable, and it's likely that much of the genetic contribution to obesity is mediated by genetic influences on lifestyle choices, rather than by genetic influences on metabolism.