Study itself is behind a paywall so impossible to gauge how well/poorly designed it was... nor find out who provided the funding!

But, John Speakman, the head of the lab from whence the study originated, has his own Wikipedia page. I think he is most famous for his "drifty gene" theory of obesity, as opposed to the better known "thrifty gene" theory of obesity.

The thrifty gene theory posits that our genetics predispose us to eat as much as possible when food is available in order to survive times of famine and, now that food is pretty much always available, and we no longer face periods of famine, we are getting fatter.

Speakman's drifty gene theory posits that humans have a broad range of genes for weight, some predisposing to skinniness and some to fatness. When we had to be able to run to escape from predators or get eaten, people with fat genes got caught and eaten more often so their fat-predisposing genes got passed on less frequently to offspring. Now that we're not subject to getting eaten by wild animals, the fat-predisposing genes are getting passed on more and more often so, as a population, we're "drifting" towards being fatter.

My take? We pretty much ceased being subject to getting eaten by predators eons ago but, rather than a slow steady increase in population weight (as one would expect) over the past thousands of years, we have witness and veritable explosion in obesity over the past half century. Drifty-gene can't explain sudden sharp uptick right AT the point in time when processed foods became very widely available AND we were told to stop eating fats and increase our carb consumption.

I think Speakman is simply trying to make himself (and his lab) "relevant" again.