The Joslin diabetes blog has an interesting article on brown fat and its effect on metabolic rate and insulin sensitivity. Brown fat is just a type of body type different from the more plentiful white fat (which is actually more pale yellow). If there are other colors of body fat, I don’t know.
If you can “activate” your brown fat, it helps you burn more calories, which could be helpful if you’re trying to lose weight. It also improves insulin sensitivity: beneficial if you have type 2 diabetes or are prone to it.
From Joslin:
“When brown fat is fully activated, it can burn between 200 and 300 extra calories per day. It is most successfully activated through cold exposure. A recent study of people with type 2 diabetes had volunteers sit in a 50 degree room for a couple of hours a day for 10 days in shorts and short-sleeved shirts.
“When I say cold, it’s not icy cold, it’s not like the winter in Boston,” she says. “It’s more or less like the temperature we have here in autumn. After this mild cold exposure, all ten volunteers with type 2 diabetes, as shown in that study, displayed increased brown fat activity and improved insulin sensitivity. This is very exciting.”
Dr. Tseng is working on understanding exactly what is happening on a cellular level to activate brown fat in the cold to see if she can create a drug that will mimic the effects. “Although cold works, it’s just not pleasant,” she says. “If you had to sit in a cold room for a few hours every day, perhaps not everybody could accept that.”
Source: How Your Body Temperature Can Affect Your Metabolism | Speaking of Diabetes | The Joslin Blog
Another way to activate brown fat is exercise (at least if you’re a man or a mouse).
Steve Parker, M.D.
Paleo Diabetic 
Question is: how little cold exposure do we need????
Did you ever follow that out-of-the-box (?crazy v early adapter?) neurosurgeon’s posts on this, years ago? I think he lived in TN, IIRC, and would sit in ice tubs, or outdoor in a tub of water when it was cold there.
Hi, Lee.
Dr. Jack Kruse? I read his blog several years ago, for a short time. He lost credibility with me although I don’t remember exactly why.
Tim Ferris seems to promote ice baths and cold exposure. Here’s an interview.
P.D. Mangan writes about potential benefits of cold showers.
I don’t do any of these techniques myself.
Ron Cronise is a also a good source as he has tested cold thermo on himself and many others. He also spent some time with Win Hof.