The alleged culprit is human adenovirus-36,or AD-36. A study published in 2002 showed
that AD-36 injected into monkeys causes dramatic weight gain. In some animals. the injected virus caused body fat to triple. It's unethical to inoculate people with viruses, of course. But in an analysis of 1,000 people, the scientists found that those with AD-36 antibodies-a sigh that they have been infected-are significantly more likely to be overweight.