The fat cat cometh

IN THEIR attempts to explain the global epidemic of obesity, researchers have often taken to fingering culprits beyond people’s direct control. It is now believed that increased levels of stress, climate change and even artificial light at night may contribute to expanding waistlines. However, if such factors affect humans, they ought, in principle, to have similarly nefarious effects on other creatures. This should hold especially true for species that are physiologically similar to people and live in proximity to them. Pet owners have long fretted that this may, indeed, be happening.

Of course, anecdotal evidence carries little weight, so a group of researchers led by Yann Klimentidis, of the University of Alabama, decided to check whether animal obesity rates do in fact mirror the worrying trend among people. They published their findings this week in the Proceedings of the Royal Society.

Dr Klimentidis and his team set about their task by scouring online repositories of scientific papers, contacting fellow researchers and even petitioning pet-food companies for data on changes in animals’ bodyweights over the decades. They limited their search to mammals, whose bodies work much like humans’ do—and, specifically, to those mammals living with or around people in the rich world.

The trawl threw up information on more than 20,000 animals from 24 distinct populations covering eight species. These included cats, dogs, mice, rats and several types of monkey. Some were bred in highly controlled research environments. Others lived in people’s homes or in the wild. None had their food intake artificially limited or, as with livestock, ramped up...