Shivering with cold may be as effective as exercise at helping us stay slim, new research suggests.
Both produce hormones - irisin and FGF21 - that stimulate the creation of calorie-burning "brown fat", a study at Sydney University has shown.
Once thought only to be present in babies, scientists now know adults also possess brown fat - and those with more of it are slimmer.
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While white fat stores energy, brown fat burns it up. Around 50 grams of brown fat can burn up to 300 calories per day, the same amount of energy stored by 50 grams of white fat.
The new research involved exposing volunteers to increasing levels of cold until they began to shiver.
Around 10 to 15 minutes of shivering produced as big a rise in irisin as an hour of moderate exercise.