TFA observes that male obesity varies in response to GDP more than female obesity does. The thesis is that increasing exposure to "female" hormones with increasing GDP explains part of this phenomenon. I haven't read this carefully enough to judge that, however.

My field of study and my experience is not in medicine or public health, but GDP vs. obesity rates seems like poor evidence for this particular hypothesis. For example, one hypothesis I can think about that explains this is that in developing countries, it could be possible that women are often homemakers, and therefore, they don't have as much physical exercise as their male peers. In developed countries, where women are more free to work, the obesity rates are comparable...

I mean, I don't see a slam dunk "See, it's female hormones!" There could be a number of things from culture to lifestyle choices to work-life balance that can have affect on obesity that might correlate with GDP. They should have at least controlled against that, and I see no evidence of it.

The correlation itself is interesting, even without the female hormones.

Being a homemaker in the developing world frequently involves a lot more physical activity than in the developed. Food and water are usually a lot less convenient, and may involve travel. Homemaking may also involve farming, and taking excess food from the garden to market which again, often involves travel.

Also, the physical effort involved in being in the workforce in the developed world can be almost nil. A lot of people have to stand up all day, or pick up boxes, but that's far from subsistence farming or hand-washing clothes.

>In developed countries, where women are more free to work, the obesity rates are comparable...

Or even: in developed countries, most work is not physical labor.

Yeah, this study seems pretty shallow and fails to take into account other indirect factors which might influence obesity rates (so it's not necessarily A->B, but possibly A->B->C->...->Z).

Human culture and gender differences is overwhelmingly complex subject. This research is trying to establish direct relationship between estrogen and obesity, but hormones might have subtle but signficiant effects on human culture.