What is metabolism?

Article written by Heidi Campo; NSCA CPT, CSCS, and certified Fitness Nutrition Specialist

What is metabolism?

We all know someone who seems like they can eat whatever they want without gaining weight. They are high-energy hummingbirds who don’t ever slow down. On the other hand, we also probably know someone who has to watch every bite of food they eat. They are slower and have lower energy. 

Both of these people give us a window into their metabolism just by the way they act. You see, your metabolism is a fancy way of saying your daily energy demands. In the scientific world, we call it your Total Daily Energy Expenditure, or TDEE for short. This tells us how many calories we burn in a day.

Figure 1

What makes up your TDEE?

Your TDEE (shown in Figure 1) is essentially made up of 4 things.

  • BMR= Basal Metabolic Rate. How many calories you burn at rest. This mostly comes from the organs that burn energy to do their job and keep you alive.
  • NEAT= Non-Exercise Activity Thermogenesis. How many calories you burn from daily movement. Like walking, talking, thinking, fidgeting, etc.
  • TEF= Thermic Effect of Food. How many calories it takes to break down the nutrients you consume. Some foods take more energy to burn than others. Some foods are very hard for the body to break down and yield a low-calorie count, like celery.
  • EA= Exercise Activity. How many calories you burn from exercise.

Basal Metabolic Rate 60%

Sometimes you will hear your BMR/ Basal Metabolic Rate used interchangeably with RMR which is your Resting Metabolic Rate. They are similar numbers, but different. BMR is how many calories your body burns at rest if you were asleep or in a coma. RMR is how many calories your body burns at rest if you are just watching TV. Your internal organs are slightly more active when you are awake, vs asleep. So your RMR is going to be slightly higher than your BMR. For TDEE (Total Daily Calorie Expenditure), we will be referring to your BMR.

Figure 2

Every cell of living tissue in your body requires energy to stay alive. The speed of your metabolism is determined by a complex series of chemical reactions. Some you can control, some you cannot. Figure 2 demonstrates some averages of where calories come from with our BMR. While skeletal muscles take up a lot of mass, they are very efficient at not utilizing energy when not needed. It’s your organs that cost the most calories per day!

The average human heart needs about 500 calories a day to keep pumping. Now factor in all the other systems that keep functioning all day every day, and this makes up your BMR. Which accounts for about 60% of your TDEE (Total Daily Energy Expenditure). Your BMR is something that can be sped up or slowed down through lifestyle changes. Things like chronic dieting will lead to a slower metabolism and yo-yo dieting. See our article on how you gain fat here!

NEAT 20%

Non-exercise activity thermogenesis, wow that is a lot of words. From the moment you wake up, brush your teeth, and walk around to get ready, until you flip off your light at night and go to sleep. All of your daily movements. Every time we move, even if we are just using our thumb to scroll on this screen, it takes a little bit of energy. Scrolling on your phone takes very little energy, but if you add up all the calories you burn throughout the day, every single movement of the day, it becomes significant in the overall equation.

Think back to the person you know who is like a hummingbird. They are always moving, they seem to do everything fast. They can’t even drive or sit still without adding extra movements. This person will have a very high NEAT throughout the day.

If you are chronically undereating, you might become more sluggish and fatigued. A sign that your metabolism is trending downward is when you stop moving around as much as you used to. You can improve your metabolism by bringing your calories back to your maintenance TDEE and working on increasing NEAT. Here are some easy things you can start doing right away to increase NEAT:

  • Park farther away from entrances.
  • Take the stairs.
  • Set an alarm to not sit for more than an hour at a time. Get up and walk around for 5 minutes at the top of every hour. (Not only will this help your NEAT score, but it will increase your overall productivity, energy, and mood)
  • Listen to music and bob your head or tap your foot to the beat throughout the day.
  • Choose a standing desk, or sit/stand 50/50.
  • Use a pedometer and try to get 10,000 steps a day. You can opt for an expensive gadget, or you can even download a free app on your phone.
  • Keep your space clean. Move about and tidy up regularly to stay active.
  • Fidget and pace if you can during calls or meetings.

Exercise Activity 10%

Here’s the deal, exercise is great. Everyone SHOULD do it, but according to the CDC, only 53.3% of Americans meet the minimum requirement for aerobic activity. With only 23.2% of Americans meeting the minimum requirement for aerobic and resistance training.

What are these minimum guidelines? The ACSM (American College of Sports Medicine) has determined that the bare minimum of weekly activity necessary to avoid disease is:

  • 150 minutes of moderate to intense aerobic activity per week
  • 2 sessions per week of resistance training to strengthen all major muscle groups.

Keep in mind this is THE MINIMUM-required exercise, and it is separate from NEAT. The majority of Americans aren’t even meeting the minimum to keep themselves from getting ill. So if you fall into the group of Americans that is achieving the minimum already, CONGRATULATIONS! Keep it up and see if you can bump it up a notch if you want to improve your physical fitness.

If you are not currently meeting the ACSM minimum guidelines, then you should focus first on increasing NEAT, and working towards the minimum guidelines. This can be achieved the easiest with daily walks and weekly calisthenics routines at home. Read this article for suggestions on how to get started!

Thermic Effect of Food 10%

The thermic effect of food is a fancy way of saying how many calories are used in the process of digesting the food you eat. Lets take celery for example. It takes a lot of the calories that you get from celery to digest it due to how much fiber and water are in celery, making it a very low calorie snack.

Lean proteins on average lose 20-30% of their total calories to the digestion process. This is because they take so much more effort for the body to break down. Which is also why high protein diets leave us feeling fuller for longer. This means that if I eat 100 calories of lean protein, then I will only get 70-80 calories from that meal.

The same goes for carbohydrates. 15-20% of certain carbohydrate foods are lost to the thermic effect. This mostly applies to whole food carbs like fruits, and veggies. Processed carbs and simple sugars will not give you the same benefit.

Dietary fats have little to no thermic benefit, meaning you get the whole 100% of the calories you eat from fat! Figure 3 shows the thermic rates for each macronutrient.

Does this mean you get to start subtracting 20% of the calories off of your steak? The answer is no. The thermic effect of food is already calculated in most calorie equations. However, you can still maximize the benefit of TEF by increasing your consumption of lean proteins and fibrous green veggies. This will benefit you greatly and will help increase your TDEE/ metabolism long-term! Along with an increased TDEE, you will also enjoy a more optimized gastrointestinal system, immunity, decreased inflammation, and improved longevity.

This is one of those things we know we should all be doing, increasing our lean protein and fibrous veggies. Many of us don’t really know WHY though. Understanding the TEF of these foods helps us understand the benefit of increasing them.

Figure 3

To sum it up

  1. Your TDEE (Total Daily Energy Expenditure) is your metabolism, you can speed it up or slow it down based on your lifestyle.
  2. Your BMR (Basal Metabolic Rate) comes mostly from your internal organs and makes up the majority of your metabolism.
  3. NEAT (Non-exercise Activity Thermogenesis) is your daily movement and it is something we can all work on increasing with a million tiny lifestyle changes that add up to big change.
  4. EA (Exercise Activity) is something that 76.8% of Americans are deficient in. Meeting the minimum guidelines will help prevent disease.
  5. TEF (Thermic Effect of Food) is how many calories are lost to the digestion process.

Are you interested in finding out exactly how many calories you need to be consuming? Schedule an appointment to meet with the nutritionist if you are an existing client. If you are coming to us for the first time, click here to sign up as a new patient!