It's not just humans. Scientists say the animals that live around us are also putting on the pounds—rats, cats, and rhesus monkeys.
Beyond the more obvious factors contributing to obesity—the food we eat, the physical things we do—there's increasing evidence that something else might be play in our environment, factors that range from viruses, light pollution, and genetic mutations to stress and various environmental contaminants. Scientists have suggested, for example, that leaving a light on at night correlates with obesity.
But how much do these things really factor into the obesity epidemic? In one recent attempt to answer that, scientists looked at studies involving 20,000 animals. The idea, Yann C. Klimentidis and the study's authors write, is:
Model organisms have potential value as ‘canaries in the coalmines’ or ‘sentinels’ informing us about environmental factors potentially impacting humans. In this light, we compiled data to assess time trends in body weight in mammalian species that live with or around humans in industrialized societies. Such observations might help identify environmental influences that might otherwise go undetected.\n
In 24 different animal populations living in vastly different conditions—feral rats in Baltimore; lab rats, dogs, and cats in New Jersey; rhesus monkeys in California, Oregon, and Wisconsin—the average body weight of the animals studied increased between five and 10 percent every decade. So despite relatively few changes in diet or exercise, there appeared to be a similar rise in animal weight. No single factor explained similar increases in, say, lab rats and wild rats.
So without dismissing the influence of food marketing, fast food, and reduced physical activity in humans, the study seems to suggest there's definitely something else going on, something else worth looking into. After all, these cats and dogs weren't watching TV and eating McDonald's and still, their weights increased significantly.