When it comes to the metabolism, most people’s definition would go something like this: “If it’s fast, you burn fat.  If it’s slow, you gain fat.”  And while there is some validity to that line of thinking, it doesn’t define WHAT the metabolism is, nor does it offer any explanation for WHY it is that way. 

In this article, I’m going to give you a practical definition of the metabolism, as well as break down each of the basic components: basal metabolic rate (BMR), non-exercise activity thermogenesis (NEAT), exercise activity thermogenesis (EAT), and the thermic effect of food (TEF). 

My hope is that having a deeper understanding will help you make your metabolism work to your benefit! 

What Is the Metabolism? 

 The technical definition of the metabolism is “the sum of all the chemical processes that occur in a living organism involved in sustaining life.”  But that’s not going to help us get to where we want to go, so I’d like to offer a working definition of the metabolism. 

The metabolism is your body’s energy production system. 

It’s that simple.  All the things our body does to produce energy can be considered our metabolism.  The conversion of the food we eat to the energy expended in activity is a part of the metabolic process.  So is the breakdown of adipose tissue (aka body fat). 

But it’s understanding the things that make up our metabolism that will create clarity around how to achieve your health and fitness goals, so let’s dive in. 

Basal Metabolic Rate (BMR) 

Your BMR (also referred to as “resting metabolic rate”) is all the energy expended in merely keeping you alive.  Imagine you were to lie still and never do anything (including eat!) – the calories you burned would be your BMR. 

Obviously, none of us do that, so the actual measurement of BMR is purely theoretical.  However, the application of BMR to body composition is important.  This is because of the significant difference in the energy expenditure between lean tissue and adipose tissue.  Lean muscle mass can burn as much as 12 calories per lb, while fat mass burns as little as 2 calories per lbs. 

This is part of the reason we stress the importance of strength training and the building/maintenance of healthy amounts of lean tissue.  Muscle is a metabolic organ, and the difference in a person’s bodyfat % can have drastically impact a person’s BMR.  Here are some numbers to illustrate: 

  • 200 lbs male @ 30% BF – BMR ~1800 calories 
  • 200 lbs male @ 15% BF – BMR ~2100 calories 

Main takeaway: lean muscle mass is important for a healthy metabolism, and for your health overall. 

Non-Exercise Activity Thermogenesis (NEAT) 

Simply put, NEAT is the energy you use to do anything other than exercise.  Cleaning the house, carrying your kids, walking to/from somewhere, etc. – these are all examples of NEAT. 

While BMR generally makes up the largest portion of the metabolism (60-70% on average), NEAT is typically the second most significant area of energy expenditure in our daily lives.  However, it’s hard to put a percentage to it because this can vary drastically from person to person.  For example, NEAT will comprise a very small portion of the energy expenditure for a person that is sedentary and spends most of his/her time sitting at a desk.  Whereas, someone that does manual labor for a living will burn a much larger percentage of his/her daily caloric expenditure through NEAT. 

While it’s hard to measure NEAT exactly, a good place to start is by tracking your daily steps using a pedometer. 

Here’s a quick example to show you how impactful this can be. 

A person that is mostly desk bound and does not exercise could walk as little as 2,000 steps per day.  Whereas, a UPS delivery driver will easily exceed 20,000 steps per day.  If we calculate that the average person burns 40 calories per 1,000 steps walked (this varies depending on the size of the person, but for the sake of simplicity we will just use 40 cals/1,000 steps), then the difference between the calories burned by a desk worker and a UPS driver is 720 calories per day!  Over time, this will have a huge effect. 

Main takeaway: the treasure trove of un-burned calories is in NEAT, especially if your goal is related to fat loss.  If you change nothing else other than increasing your step count 1,000-2,000 steps per day, you will likely start to make progress. 

Exercise Activity Thermogenesis (EAT) 

This is the one I’m going to spend the least amount of time on because it’s the one that most people already understand the importance of.  However, I will share these two important points as it relates to exercise. 

First, every exercise program should include some form of resistance/strength training.  Based on what was discussed above in BMR, there should be an intentional focus on cultivating lean muscle mass.  Not to mention, it’s one of the most effective forms of exercise for fat loss (but that’s another article). 

Second, you should exercise often, but don’t fall into the trap of thinking the only way to lose weight/burn more calories/boost your metabolism is to exercise as much as possible.  In particular, don’t spend hours and hours grinding it out doing cardio. 

Main takeaway: the focus of your exercise program should be strength training.  Cardio is supplementary.  And NEAT will likely play a bigger role in energy expenditure than EAT (unless you’re an athlete). 

Thermic Effect of Food (TEF) 

TEF is the energy expended during the breakdown of food for use or storage.  Yes… you burn calories while digesting your food. 

While TEF is generally the smallest portion of the metabolism (usually estimated at approximately 10% of total caloric expenditure), it should not be underestimated.  Given the fact that we eat multiple times per day, the small differences will compound over time and can have an impact on whether or not you end up with a “slow metabolism” as you age. 

To demonstrate this point, here are some numbers on TEF for various foods: 
 

  • Protein TEF can be as high as 30% 
  • Fats TEF can be as low as 3% 
  • Liquid sugars are 0-1% 

If you consider the fact that whether or not you gain/lose weight is determined by the delta between the energy you consume and the energy you expend, then it makes sense why you would want to favor foods with a higher TEF.  (This is a general statement, as there are times when low TEF foods are preferable – for example, fats are low TEF, but complete elimination of dietary fat would have a negative effect on one’s health.)  Yes, 100 calories of protein and 100 calories of sugar are still both 100 calories, but the former will create more metabolic activity than the latter. 

Main takeaway: eat lots of protein and avoid refined/processed sugars. 

Conclusion 

Metabolism is unique and will vary from person to person.  It is also dynamic and will change over time.  And it doesn’t necessarily “slow with age” – it slows based on poor lifestyle choices, the worst of which is chronically consuming more calories than you burn. 

If you want a metabolism that runs like a HEMI V8, then focus on STRENGTH TRAINING and eating enough PROTEIN.