Evolving data suggest that a notable inflammatory, and possibly infective, etiology may exist for obesity. Adipose tissue is known to be a repository of various cytokines, especially interleukin 6 and tumor necrosis factor-alpha. One study showed an association between obesity and a high-normal level of plasma procalcitonin, a dependent variable that reflects a state of distress or inflammation.

Data have shown that adenovirus-36 infection is associated with obesity in chickens and mice. In human studies, the prevalence of adenovirus-36 infection is 20-30% in people who are obese, versus 5% in people who are not obese. Despite these provocative findings, the roles of infection and inflammation in the pathogenesis of obesity remain unclear.