Breaking BAT: can browning create a better white?

Obesity and its comorbidities are a growing problem worldwide. In consequence, several new strategies have been proposed to promote weight loss and improve insulin sensitivity. Recently, it has been demonstrated that certain populations of white adipocytes can be 'browned', i.e., recruited to a more brown-like adipocyte, capable of thermogenesis through increased expression of uncoupling protein 1. The list of browning agents that induce these so-called beige adipocytes is growing constantly. However, the underlying mechanisms are often poorly understood, with the possibility that some of these agents cause browning as a secondary effect. Moreover, it remains unclear whether beige adipocytes can contribute sufficiently to affect whole-body energy expenditure in a functionally significant manner. This review presents an overview of the different molecular pathways leading to the induction of beige fat, including direct stimulation and indirect actions on the CNS or the immune system. We discuss the available evidence on the capacity of beige adipocytes to influence whole-body energy expenditure in rodents, and lastly outline the potential problems of translating browning capacity into the potential treatment of human metabolic diseases.