How do we keep warm?

We put this question to Professor Roger Thomas, from the University of Cambridge:

Roger - I'm Roger Thomas, a Professor of Physiology in the University of Cambridge and I do lecture to medical students on thermoregulation. What we should start with is saying that we're all producing heat all the time by the chemical processes in our bodies. For example, the heart, pumping blood around the body, uses energy derived from glucose, and the mechanical energy from glucose is produced with waste heat. So all the time the heart is working, it's producing excess heat. All the other chemical processes going on in the body, digesting food, thinking and so on, the amount varies, so after a heavy meal you produce a lot more heat as you digest it than normally.

I expect the question you really want to know about is producing heat when you need more than normal. There are two mechanisms there. One will be very familiar to most of you - shivering. This involves involuntary contractions of large muscles which generates heat wastefully, as it were, but in this case you need the heat to keep warm. The other mechanism is known as non-shivering thermogenesis, or heat produced by mechanisms other than shivering. This primarily involved brown fat. These are cells in patches of tissue all over the body, particularly near the heart, in the shoulder blades and so on, which are very important in newborn babies, who have a lot of trouble regulating their body temperature. In adults it's also found, although this has been controversial, and this works by simply burning glucose to produce heat rather than any other form of energy. It's a 100% heat production process, and this tissue is located near blood vessels, so it warms up the blood and warms the whole body.

Diana - Brown fat is great for burning glucose and producing heat. It has been hypothesised that people who live in houses without central heating tend to have higher proportions of brown fat.

But then, central heating is another form of thermo regulation - along with clothes and blankets.

And a paper published in Obesity Reviews in January actually showed evidence that living in warmer houses is contributing to obesity - and this could be related to reduced proportions of brown fat against white fat.