Very low-calorie diets — shown to boost longevity in some mammals — can turn white, energy-storing fat into beige, energy-burning fat in mice.

Calorie restriction and the accumulation of beige and brown fat have both been associated with metabolic benefits such as increased sensitivity to insulin. To look for a link between the two, Mirko Trajkovski of the University of Geneva in Switzerland and his colleagues cut the calories given to normal-weight and obese mice by 40% and found that this triggered the browning of white fat into beige fat in both types of animal.

The restricted diet also raised the levels of certain immune-system proteins called cytokines. Mice that were genetically engineered to lack responses to these cytokines did not turn fat beige in response to caloric restriction — and also did not experience many of the metabolic benefits.

Cell Metab. http://dx.doi.org/10.1016/j.cmet.2016.07.023 (2016)