HUNTINGTON BEACH, California, January 25. BAT or Brown Adipose Tissue (also known as brown fat) are recently discovered brown-colored cells that consume calories and generate heat while activated by the cold. Considering the amount of time that many open water swimmers spend in the cold water and shivering in temperatures in their swimwear while others are bundled up in warm clothes, it may be probable that open water swimmers are rich in brown fat relative to other athletes.
BAT is a specialized highly vascularized tissue whose function is to produce heat. It is filled with mitochondria that contain iron, giving the tissue a reddish brown color. In adults, BAT is located in the upper back, on the side of the neck, in the dip between the collarbone and shoulder, and along the spine. Infants have it mostly as a sheet of cells covering their backs.
Researchers believe that thinner people have more BAT than heavier people; younger people have more than older people; and women have more than men.
When I first started on this journey to conquer the English Channel, people emphasized two things to me:
1. Cold exposure: I needed to spend a lot of time in cold water so that I would "get used to it"
2. Weight gain: Nearly everyone who found out I wanted to swim the Channel would look me over and say, "you're gonna have to put on some weight."
This raised some issues in my head. To address the second point, intentionally gaining weight for an athletic endeavor seems unhealthy to me. To address the first, what does "getting used to it" actually mean? It can't just be a mental thing that allows your body to adapt to spending hours on end in cold water. There had to be some corresponding physiological change that allowed the body to tolerate cold better.
The Difference Between a White Fat Cell (fat storage) and a Brown Fat Cell (heat factory)
One possibility people have raised is the existence of brown fat. Unlike white fat, which is found under the skin, deposits of brown fat are present around vital internal organs and along the back and sternum. Further, brown fat has mitochontria: it is metabolically active. White fat is not. This means that brown fat is capable of generating ATP. Or, more simply, brown fat generates heat.
The only problem with this theory is that brown fat was only thought to be present in infants. No one had ever detected brown fat in adults. However, in the April publication of the New England Journal of Medicine, not one, but three independent labs proved the existence of brown fat in adults. Further, using different experiments, all three groups demonstrated that prolonged exposure to cold resulted in an increase in an adult's amount of brown fat.
Summary: brown fat generates heat. Exposure to cold increases an individual's brown fat. More brown fat = more heat = you can stay warmer in cold longer.
Going back to the two points: point 1 addresses the way to increase brown fat, while point 2 addresses the way to increase white fat.
Sure, white fat can provide "some" increased insulation. But brown fat not only insulates the core (the most important part of the body to keep warm), it also acts as a heat factory. Hence the way you can "get used to" the cold.
Here's an even cooler implication of this discovery: you can train for the Channel even when you aren't actually swimming. Any time you expose your body to the cold, you are helping your body produce more brown fat, thereby increasing your cold tolerance.
In light of these publications, I'm finally taking the advice of my friend: I'm now going around with bare legs and flip-flops, whether rain, shine, wind, whatever, intentionally exposing myself to being cold to increase my brown fat stores. In my opinion, it's a more healthy approach to cold water swimming, though it earns me some funny looks when I'm sporting a skirt and Rainbows in the arctic South San Francisco winds.
For the abstracts of these papers, see:
Courtesy of Open Water Source