That Time When BATman and Mr. Freeze Were on the Same Team

 Executive Summary

This post is presented to you at the request of my sister who said in a Facebook response to my post(s) on Intermittent Fasting:


So, ignoring the comment about body hair, this post will describe:

You get all this with the simple request from my sister because she’s smart enough to know that if you increase your metabolism, you increase the amount of calories you burn.  And if you increase the amount of calories you burn, you also increase your ability to control your weight.

Metabolism And What You Can Do

In L4‘s series about Intermittent Fasting,  we discussed how the only (healthy) way to lose weight is by running a calorie deficit (i.e. burning more calories than you consume).  It is clear to everyone how calories are consumed but there are a lot of myths about how calories are burned. Calories are burned in a near infinite number of ways but they can be categorized as follows:

  • Resting Metabolic Rate (RMR) – The calories your body burns just to stay alive.  This is technically different from another term you may have heard, Basal Metabolic Rate (BMR), but for the purposes of this discussion we can assume they are the same.  Lots of systems, organs, and individual cells in your body contribute to your total RMR but the top 3 consumers of calories are your liver, brain, and skeletal muscles.  Half of your RMR is based on the calories burned by these three.  More than 2/3s of your total calorie burn comes from your metabolic rate.
  • Thermic Effect of Feeding (TEF) – The calories your body burns in the act of digesting food and absorbing its nutrients.  The TEF represents 10-15% of total calorie burn.  There are lots of myths based on the TEF.   For example, while it is true that if you fast, it causes a drop in metabolism, what we’re really talking about is the TEF.  That’s a drop of no more than 15% that lasts only as long as you’re fasting.  Not worth worrying about.
  • Physical Activity – Physical Activity includes the calories you burn from exercise plus any other additional activity you undertake including walking, climbing stairs, doing housework, etc.  This additional activity is sometimes called NEAT for non-exercise activity thermogenesis.
Percentage Contribution to Daily Calorie Burn
Percentage Contribution to Daily Calorie Burn

If, in the interest of losing weight, you want to increase your calorie burn, these are the three areas where you can have a potential impact.


You have limited short-term control over your RMR.  The way to have the most long-term effect on your RMR is to gain weight.  Regardless of whether that additional weight is fat or muscle, your metabolism will go up.  More cells, higher metabolism.  However, fat cells don’t burn very many calories (spoiler alert→there is an exception).  Most of the metabolism increase that happens when you add fat comes from the amount of additional support (wear-and-tear) the rest of your body provides to keep you alive.  Muscle tissue, however sits at number 3 of the top 3 consumers of calories even when you’re at rest!  So replacing fat with muscle clearly seems worth it if you’re interested in sustained weight loss.

As an aside, while your brain consumes another 15% of your total calorie burn, there isn’t much you can do to change that.  Thinking harder doesn’t really increase how much calories the brain burns.  Even something like sleeping doesn’t change the calorie burn of the brain.  There is interesting research to be done however about how mindfulness activities like meditation may impact the brain’s use of energy and we’ll discuss that in a future post.


By definition, the more you eat, the more calories you burn through feeding’s thermic effect.  However, in most cases, you’re going to consume more calories from eating than you burn by eating.  The exception is if you increase your pure fiber consumption and while most people consuming a North American diet could benefit from eating more fiber, too much fiber can lead to unpleasant consequences for you and everyone around you.  Nope, your opportunities to increase your daily calorie burn through TEF are limited and the overall impact will be small anyway given that TEF as a whole only represents 10-15% of the total burn.

Physical Activity

This is where you have the most opportunity to impact your daily calorie burn because the amount of physical activity in your life, whether from exercise or NEAT, is mostly within your control.

The bar graph below is an example of two people who might be very similar except one is sedentary and one is active.  For the purposes of this example, I assumed their RMR (or BMR) is the same.  This is because although the active person may have more calorie burning muscle, the sedentary person may weigh more and we get a wash.  The TEF is virtually the same and even if it is different it is such a small percentage of overall burn that it isn’t worth worrying about.  The nice thing is that even though this limits your opportunities for increasing your total calorie burn to physical activity, there are so many pleasant ways of being active, even if you don’t like to exercise.

Components of Daily Calorie Consumption
Components of Daily Calorie Consumption

 Hacking Your Metabolism with Cold Exposure

While options for making short-term and lasting increases of your metabolism are limited, one area of opportunity is via cold exposure.  In your body’s everlasting quest to maintain homeostasis (equilibrium), when your body is exposed to extreme cold, it undergoes a number of processes to help keep your temperature at its beloved 98.6° F.   Short term, the hypothalamus conducts the following ballet:

  • Blood flow is constricted in the outer reaches of your body so all that warm fluid can keep your organs nice and cozy.  This is why you feel that same pins-and-needle feeling in your fingers and toes when they’re cold that you feel when you cut off their blood flow.  This is the opposite of what happens when you’re overheated.  When overheated you may see more veins than usual exposed under your skin.
  • The fine hairs rise from our bodies and we get goose bumps.  This is no doubt a leftover from our prehistoric ancestors who had more body hair than most of us (Partial Neanderthals like myself excluded).  By puffing the hair away from the body you get an extended layer of insulation.  (Hey Sis I did work the body hair discussion into this post!)
  • Your muscles shiver and your teeth chatter.  This is where most of the additional calorie burn comes from.  All that micro-movement adds up and burns additional calories.

But the above adaptations only really effect metabolism in the short-term.  Your body has another trick up its sleeve to protect you if you have frequent and sustained exposure to cold and that is what allows me to explain…

What Does BATman Have To Do With Any Of This?

Well actually the trick isn’t so much up sleeves as it is inside your chest and upper back.  You see, even though I said earlier that fat doesn’t burn many calories, that isn’t the whole story.  When you were a baby and more vulnerable to the cold, your body had extra insulation that was comprised of a very special kind of fat.  This fat burns calories like muscles do and its main purpose is to keep you warm.  These special fat cells have lots of mitochondria in them and mitochondria are the main producers and consumers of energy in ourcells.  The end result is an increased metabolism.

As you grow up your body loses much of this special fat but you can coax it back by sustained and repeated cold exposure.  There is a whole movement around this that you can learn about here.  Some of the techniques people use to try and cultivate this fat include:

  • Walking around on extra cold days while wearing minimal clothing
  • Frequent immersion in cold swimming pools, cold baths, or taking cold showers
  • Applying ice packs to the upper back on a daily basis where most of this special fat is stored.

I have personally tried the second two and they are ass unpleasant and/or inconvenient as they sound.  But to some people it may be worth it.  Personally I prefer exercise.  Furthermore, there is a lot more research that needs to be done to understand both the viability of cultivating this fat as well as the potential side effects.  For example, some preliminary studies in mice link this type of fat to increase arterial plaque.  It is important to note that in most cases, mice are not people.

But still, what does any of this have to do with BATman?  Well, all those extra mitochondria in these special fat cells change the color of the fat from it’s usual pristine white to a shade of brown.  And the technical name for this type of fat is Brown Adipose Tissue (or BAT).

Yes, this was an awfully convoluted tale whose conclusion is merely a bad pun, but hopefully you learned something in the process.  If you didn’t, you can blame my sister.  She’s the one who asked for it in the first place.

Meanwhile, for more bad puns, stay tuned.  Same BAT time.  Same BAT channel.

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