Shivering may burn more kilojoules than workout

The two activities increase levels of two hormones known to be instrumental in that process —irisin, produced by muscle, and FGF21, produced by brown fat. 

People with more brown fat tend to be slimmer and have lower glucose levels than those who have less.

Endocrinologist Dr Paul Lee showed that when 10 healthy adult volunteers were exposed to temperatures cold enough to make them shiver, which occurred between 14°C and 16°C, they produced the same amount of irisin in less than 15 minutes as was produced after an hour of moderate exercise.

“We speculate exercise could be mimicking shivering because there is muscle contraction during both processes, and that exercise-stimulated irisin could have evolved from shivering in the cold,” Dr Lee said. 

While 50g of white fat stores more than 1255.2 kilojoules (300 kilocalories) of energy, that amount of brown fat can burn up to the same number of kilojoules, he

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