How could a virus make you fat? When fat cells are exposed to AD-36,they begin to multiply. “We are not saying all obesity is caused by a virus.Genes, metabolism, and habits all play a role,” the scientists acknowledge. “Butat least one other possibility appears to be infection.”4 As yet, no one knows how widespread AD-36 may be, or how big a role itmight play in the current obesity epidemic. If the scientists’ suspicions provecorrect, the next step would be to develop a vaccine.