What is Metabolism?
The term metabolism gets thrown around a lot. But, what exactly is it? Rather than you spending hours trying to figure it out on your own, I'm going to make it simple here. Our metabolisms are very complex, but there are a few main ways to break it down to better understand what the term really means.
Metabolism is simply a sum of all the chemical processes that go on inside of us to sustain life.
We can look at our metabolism (very simply) as our TDEE, or our total daily energy expenditure. When you hear the term "fast" and "slow" metabolism, that is really just a low or high TDEE. Our metabolisms are not static. They change and adapt based on current energy balance (calories in vs out), hormones, micronutrient availability, and more. Let's go over the 4 components of our TDEE (what makes up how many calories we burn in a day).
- BMR: This stands for basal metabolic rate and accounts for the calories burned just to keep you alive (heart pumping, breathing, etc). This accounts for the highest percentage of your TDEE.
- BMR is impacted by total body weight as well as body composition. A heavier person is going to have a higher BMR. It makes sense if you think about it...they have more "body" to keep alive. Conversely, two people who weigh the same may have different BMR's due to a difference in body composition. If one person has more muscle mass as compared to fat mass, their BMR will be higher. Muscle is an energetically expensive tissue and uses up quite a bit of energy just to sustain.
- This is one reason why your metabolism may "slow" or "speed up" in a fat loss phase or a bulking phase, respectively. If you are losing weight, you are a smaller being and therefore, require less energy to sustain life. If you are putting on new muscle, your body will spend more energy daily maintaining that tissue.
- TEF: This stands for the thermic effect of food and accounts for roughly 10-15% of your TDEE. Fun fact, protein has the highest TEF (aka it burns the most calories to digest, though still not a very significant number).
- Again here, we can see how this may "slow" or "speed up" our metabolism. If we are eating more food, our bodies are having to use more energy to digest and utilize that. If we are eating less food, our bodies are using less energy, in comparison.
- PA: This component of metabolism accounts for physical activity and differs largely person to person. We can think of this as our planned exercise (lifting weights, doing a workout class, etc). This one doesn't take much explaining. Some exercise burns more calories than others (don't forget- some exercise continues to burn calories in the repair process as well so don't get too caught up in what your fitness watch says).
- NEAT: This stands for non-exercise activity thermogenesis. So, things such as fidgeting, maintaining posture, activities of daily living, and so on. This also differs widely by person. Think about it...some people build houses all day, some people sit at a desk.
- NEAT takes a HUGE hit when we are in a caloric deficit. We can be mindful of this and attempt to offset it a bit by intentionally getting in steps, etc. but it will still be impacted, regardless. Now, don't freak out! This is totally normal and okay! But this is one reason the metabolism "slows" in a dieting phase. Subconsciously, you won't fidget around as much. Your brain may make decisions such as "I'll go get the mail later" whereas before, you may have had energy to do lots of random tasks throughout the day.
- Conversely, in a surplus, NEAT will increase! And therefore, increase our TDEE (calories burned throughout the day)
All of this sounds great but now you may be thinking..."but if being in a caloric surplus increases our metabolism in all of these scenarios, why wouldn't that be correlated to fat loss?" The reason is simple...you are also eating more. So, in reality..things are balanced out. Our metabolisms are very very smart and very adaptive (some people have more adaptive metabolisms than others). Also, keep in mind TDEE may change slightly day to day. Some days, you may walk around more than others (traveling, etc.) and some days, your workout may not be as intense. That's 100% okay! The goal here is for you to just UNDERSTAND what metabolism is.
How can you use this information?
By knowing roughly how many calories you burn in a given day, you can determine the amount you need to be eating in order to lose weight, maintain weight, or build muscle (and gain body fat if necessary). *The following are all recommendations based on my experience and knowledge and should not be used to treat, prevent, or cure any illness or disease.
- To lose body fat, a good run of thumb is to create a ~15-20% deficit from your maintenance to start. As you metabolism adapts, you can create smaller changes by either decreasing food intake slightly and/or adding a bit more cardio.
- To maintain, that's pretty straight forward. You will want to eat at around your TDEE.
- To put on muscle, you will want to create a caloric surplus. Keep in mind, our metabolism is adaptive, so you will want to keep making increases (at least for a while) here as well just as you keep making adjustments for a deficit when needed. In order to minimize fat gain in a muscle building phase, I recommend slowly increasing calories (through carbs and fats, keeping protein steady) as you go.
In order to determine your TDEE (if you haven't been tracking prior- if you have, just use the numbers you already have to adjust), you can:
- Keep track of your food intake for ~3 days and get an average of what you normally eat. From there, you can set a baseline to start from based on whether you have been losing, maintaining, or gaining at that intake.
- Use a calculator. These won't be 100% accurate as they don't know your diet history, hormone profile, etc. but it can be a good baseline to start from and adjust as needed! Here is a link to a BMR/TDEE calculator --> http://www.bmi-calculator.net/bmr-calculator/harris-benedict-equation/
I hope this article was helpful for you! Feel free to share this if you found it useful.
