How to

9 January 2017

The Architecture of Fat: It’s More Than Insulation


Everybody knows that body fat helps people retain a higher body temperature. However, beyond noting that “it’s insulation,” how does body fat actually work? The answer, really, is quite multifaceted – and requires an understanding of the specific composition of the stuff itself.

Firstly, the relative density of blood vessels in body fat is quite low. According to experts, whereas muscles and bones have routine jobs, body fat just sits there most of the day like a couch potato. Consequently, it doesn’t need many blood vessels running through it, feeding it oxygen and taking out waste products like carbon dioxide. The lack of blood vessels means the body’s blood is generally kept away from the skin – and that’s enough to significantly curtail the rate at which heat contained in the blood escapes into the body’s colder surroundings.

What’s more, fat cells also store calories. Every pound of fat contains about 3,500 calories – meaning that, to lose weight, you’ll need a deficit of 3,500 calories for every pound you want to shed. In terms of keeping warm, however, all that extra energy can be invaluable when things get chilly because burning it is the primary way in which human bodies generate heat. With extra calorific reserves, your body has the stash it needs to brace for winter. This is particularly true when there’s a significant drop in temperature; when the skin gets really cold, the thin layer of subcutaneous fat underneath begins to generate heat, helping raise the temperature of the core and reducing the likelihood of death.

However, there are certain things about fat which hold it back. In terms of consistency, for example, the stuff could be better-suited to its job. Specifically, its density is significantly lower than that of other body tissues. Bones, for example, tend to occupy 1.7g/ml, whilst both blood and muscle take up between 1.0g/ml and 1.1g/ml. Meanwhile, the density of fat is comparatively low – occupying roughly 0.9g/ml. Compared to muscle, therefore, fat is some 18% less dense.

Now, if we were talking about clothing – where it’s generally the case that fluff equals warmth –the fluffier the better. However, organic body tissues are full of tightly-packed cells, not pockets of warm air. Therefore, we need to talk about heat generation rather than fluff. Specifically, the low density of fat is rooted in its larger cells, of which there are, consequently, less per cubic centimetre. Bearing in mind that cells can produce heat, it could be a case of the more the merrier when it comes to body tissues keeping us warm. Muscle, for example, can be better than fat at generating heat; because the former has more cells per cubic centimetre and plays a greater role in respiration. Nevertheless, fat gets away with this, mainly because the types of cells which comprise it, whilst bigger, are great for storing calories. The trade-off, then, is worth it; and we’re better off with fat than without it.

So, it’s the specific architecture of body fat which makes it a highly-optimised biological tissue for doing its warming work. Yes, a thick layer of anything would inevitably help insulate a person, but it’s the specific make-up of body fat, with its few blood vessels and high calorific content, which makes it particularly well-suited to the job. So, let’s all thank evolution for this excellent insulator, and be proud of our muffin tops when winter rolls around – but let’s also hope than evolution carries on rolling. After all, fat could always be a little bit better.  


James Stannard

James has a Bachelor’s degree in History and wrote his dissertation on beef and protest. His heroes list ranges from Adele to Noam Chomsky: inspirations he’ll be invoking next year when he begins a Master’s degree in London.