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.