Brown Fat, Good Fat

January 12, 2015

Brown Fat, Good Fat 

 References:   Seale, Diabetes , van der Lans JCI Images from van der Lans, Cypess NEJM   

 It’s cold.   Wisconsin gets cold but this is extra lousy.   Last winter, it lasted for months.   Yet, my squirrels sit out there on the feeder and look toasty warm. How do they do it?     Brown fat. Ever heard of brown fat?   You had a lot of it, once. As a newborn, a fair amount of your fat is brown fat.   It is stored in the greatest amount between your shoulder blades. But check out the image link above for where PET scans show you to have fat. The amount regresses rapidly as you age, and adult humans don’t have much.   But, we keep ourselves warm all the time.   

Squirrels and rodents in general have a lot of it.   They don’t have central heating in their dens. What is important about brown fat? It has a unique protein in it that takes the energy you might normally convert into your internal gasoline called ATP, and instead makes it into heat.   That’s it. It simply turns on an internal heater that keeps you warmer without shivering. It’s called NST or Non-Shivering Thermogenesis. Of course, you would be burning energy but you aren’t actively moving muscle to do it. Instead, you get all the energy turned into heat. The protein is called UnCoupling Protein or UCP-1 if you want jargon.    

Regular skeletal muscle doesn’t have UCP. All it can do is shiver. Now, Cypess in the NEJM reference above did a brilliant study showing that humans have a lot of brown fat. It shows up actively on PET scans, looking for cancer, as little hot spots.   But people who have been kept warm all the time, never need to develop their brown fat and have much, much less of it. 

Hmmm. Can you develop your brown fat?   Can you get used to the cold?   Well, aren’t you feeling a bit more used to winter now than you used to be? Remember how cold you were that first day in November when we had the first return of the dreaded polar vortex? Yes, you do get used to the cold. You get acclimatized to it. It is a result of developing your brown fat.   

How do we know that? That what van Der Lans article is about.   He took 17 healthy young adults (23 +/- 3 years) and exposed them to 6 hours a day of temperature of 16 degrees celsius (60o F).     They did that for 10 days, then repeated PET scans on them to measure the change in their brown fat.   Results: a lot more brown fat, less shivering, less feeling cold,   Non-shivering thermogenesis or NST increased from 10% to 17% and their resting metabolic rate increased. Women went from 6.2 to 6.9 MJ/hour of resting metabolic rate.   Men went from 7.6 to 8.5 MJ.   They were acclimatized to the mildly cold temperature. But did you get that?   

You can turn up the rate at which your basal metabolism is cooking along. Could this be a way of losing weight and controlling diabetes? Yes! That’s what Seale’s article is about. As animals get fat with forced feeding experiments, they make more brown fat.   Their bodies are trying not to gain weight by having their NST turned on.   They stay hot all the time as an effort to get rid of their extra calories. Cold may be your friend. You just have to get used to it. 

 WWW. What will work for me.   Well, I’m out in this miserable cold every day, off and on.   I’ve not been hiking or walking as much as I would like because I don’t want to break an ankle. But I am turning our thermostat down at night.   I wish I could get a PET scan and see how much brown fat I had stored up. 

 Pop Quiz

  1. Brown fat is what keeps animals warm in winter – that’s how the squirrels are staying alive right now (-8o). T or F.              Answer:   True
  1. Humans have brown fat? T or F.                 Answer:   Also true. Especially just as we are born.
  1. Most of our brown fat is between our shoulder blades?   T or F.                Answer:  True, also around our torsos
  1. We can make more brown fat by being exposed to 60o temperature for 10 days.   T or F           Answer:      True
  1. Brown fat has been proven to help us lose weight? T or F.                 Answer:  False. Not proven yet, but very intriguing.
  1. As animals get obese, they make more brown fat? T or F                     Answer:   Also true. And stay warmer – as though they were trying to get rid of the extra fat.