Energy-storing white fat can be converted to energy-burning brown fat by suppressing a cell-signalling pathway. Sushil Rane at the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland, and his group report that mice lacking the protein SMAD3 are more sensitive to insulin and gain less weight on a high-fat diet than normal mice. The authors found that loss of SMAD3 caused white fat (pictured top) to take on certain key features of brown fat (bottom), such as the generation of more mitochondria, which power the cell. SMAD3 is part of the same pathway as the protein TGFJ5. Administering TGFFurthermore, a survey of 184 non-diabetic humans revealed a correlation between TGFJ3 levels and body-mass index.
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