[captainmuon]

Could different water treatment be an issue? Maybe the chemicals don't get filtered out as well in the UK as in other countries.

In the end, antibiotics surely are part of the obesity pandemic. We give them to animals to fatten them, after all. But I see not reason why it has to be monocausal. There are a lot of chemicals that look problematic (to an interested lay person like me), for example phthalates, xenohormones, or even artificial sweeteners and seed oils. It's going to take a lot of work to investigate them all.

[jeltz]

If it was water treatment wouldn't we expect to see more obese people in the cities which are further downriver and where there is more pollution in general? What we actually observe is that citydwellers have less issues with obesity. No, these might be minor factors but there are obviously factors which matter more than pollution and antibiotics.