Brown fat vs. white fat

I’ve been doing a bit of reading on some new research papers on body fat (adipose tissue).

Most (almost all) of the fat in our bodies is white fat. Fat stores energy and acts as an insulator. White fat specifically, which could be up to 25% of body weight, does not generate heat.

Until last year, brown fat was only thought to occur in infants because they can’t shiver and that it disappears in adults because we can shiver and don’t need it.

However new research papers in 2009 showed some very good news for OW swimmers.

Most of the initial interest in this seems to be around using brown fat to act as a calorie burner to reduce adult obesity. Pity they didn’t test some OW swimmers who’d be willing to act as serious cold guinea pigs.

Apparently 20 to 80% of adults have some brown fat tissue (and women more than men). This is good news because brown fat, unlike white fat, also acts an energy generating source. It has mitochondria and can generate ATP (adenosine triphosphate*), which is the main source for metabolism, as well as acting as an insulator. (BTW, brown fat cells are only about 50% the size of white fat cells which is more good news).

So that’s good news.
Even better: Guess how you activate the growth of brown fat in the adult human body?

Exposure to cold…

PET scans showed brown fat increases around primarily the neck and upper thorax after exposure to cold for a few hours.

So when one thinks about the old stories of getting acclimated to cold by repeated exposure, it appears this process may have been activated.

(This also finally explains for me how to reconcile the whole 2nd Law of Thermodynamics with energy loss in the human body changing with acclimation, which I always thought bogus. I guess I can pull my open question from Wolfram-Alpha.)

It also explains (along of course with a rare nice sunny warm day) why I could do a fairly comfortable 40 minutes today in 8.3 degree Celsius water when 2 years I was only starting swimming without a suit around this time of year.

All this is my psychopathology. Telling me something will get you no-where, I need to understand. I’m not good at “just accept it”.

*(Ernest Maglicho has a great chapter on the energy system in “Swimming Fastest”).

Story on brown fat

6 Research papers


One thought on “Brown fat vs. white fat

  1. Ah, another great post…makes a lot of sense when I think about how I am much more “acclimated” to the cold water than I used to be. Truly, yours is a great source of information (and inspiration!) about cold water swimming. I remember doing a web search on this a couple of years back and finding little…what I did find was intriguing, but wasn’t enough for me who was out there in the cold day after day (loving it, by the way). Thanks.


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