What Is Metabolism and Can We Rev It Up?

Metabolism gets blamed for all our problems. Can’t lose weight? Must be a sluggish metabolism. Can’t build muscle? Blame it on a fast metabolism. Justin Bieber writing new songs—metabolism probably had a hand in it. But do we really understand what metabolism is? And can we rev up our metabolic engines to burn more calories?

What Is Metabolism?

Think about all the complex processes it takes to drive a car. The electrical system, transmission, engine, brakes, and fuel system all have to work in concert to get you from A to B. And without fuel, nothing works.

We can use the car analogy to explain metabolism. The fuel is the food that powers all our basic life-sustaining activities like movement, breathing, contraction of the heart, and repair. Or, put another (boring textbook) way:

Turning chemical energy into a form the body can use requires a series of chemical reactions called metabolism. Metabolism is the sum of biochemical reactions that occur in the cells of the body to obtain usable energy from food in the form of adenosine triphosphate (ATP).

Just as a car requires a constant supply of fuel, our bodies need a constant supply of energy (measured in calories) to keep us functioning and alive. But unlike a car, our metabolism is always at work.

How Is Energy Used?

The majority (around 60-80%) of energy we use is for basic functions while at rest. This is known as your resting metabolic rate. Another 10% is used for digesting food, known as the thermic effect of food. The remaining 10-30% is used in physical activity. Our metabolisms are dynamic systems, so these numbers are in a constant state of flux.

The energy used for physical activity can vary considerably if you’re highly active. It’s also split into two categories:

  1. Exercise: this covers activities like weightlifting, running, and riding your bike.
  2. Non-exercise activity thermogenesis (NEAT): this covers minor movement outside of exercise. Things like fidgeting, chewing, and moving around the office.

When we add the energy used for resting metabolic rate, digesting food, and physical activity, we get our total daily energy expenditure:

TDEE graph

Can You Increase Your Metabolism?

When people talk about fast and slow metabolisms, they’re usually referring to resting metabolic rate. This is determined based on your genetics, height, age, weight, and gender—most of which are not under your control (unless you’ve worked out how to time travel).

Resting metabolic rate is the hardest to change. Physical activity is easily influenced by moving more (jumping jacks, anyone?). So, let’s look at how we can burn more calories throughout the day by targeting each of the three components that make up our metabolism.

Resting Metabolic Rate

Your body’s fat-free mass (slow and hard to change) has the biggest impact on resting metabolic rate. Most of the other determinants are out of your control. But that doesn’t mean you can’t move the needle. Here are three ways you can increase resting metabolic rate:

Post-Exercise Burn

Exercise doesn’t just burn calories while you’re sweating you ass off in the gym. Working out can increase your metabolic rate after exercise. This is known as excess post-exercise oxygen consumption (EPOC). EPOC can last for more than a day after you stop exercising. High-intensity (anaerobic) work will result in higher EPOC than aerobic activities like running. But aerobic activities tend to burn more calories during exercise.

Muscle Mass

There’s a reason why bodybuilders can eat like horses—they have huge amounts of muscle. Muscle requires more energy than fat to maintain. At rest, your muscles use about 6 calories per lb a day. Fat uses around 2 calories per lb a day.

Bodybuilders also burn a lot of calories through their anaerobic (weightlifting) workouts.  And use additional energy to build and repair muscles.

Temperature Regulation

This one’s for the biohackers out there that are willing do get all Wim Hoff and take cold showers or ice baths.

Your body has to work hard to keep your core temperature constant. It’s estimated to use around 40% of your resting metabolic rate to regulate body temperature. For every degree Celsius increase in your core temperature, resting metabolic rate can go up 10-13%. So, cranking the AC in winter, cold showers, or ice baths can help burn more calories.

Thermic Effect of Food

Remember that around 10% of our total daily energy expenditure is used to break down food.

Your body uses a lot more energy to break down protein than it does to break down fats and carbs. This is why protein is a staple in many diets. By simply eating more protein-rich foods, you’re fuller for longer and burn more calories.

Here are the different thermic rates for macronutrients:

  • Carbohydrates: 5–10%
  • Fats: 0–3%
  • Proteins: 20–30%

Put another way, if you eat 200 calories of protein, your body could use up to 60 calories digesting it. You can see how this could add up over time to keep your metabolism working hard.

Physical Activity

Physical activity is the component of our metabolism that varies the most. It’s also something we can directly change by exercising or moving more. Most people get that part. But what can we do outside of exercise to burn more calories?

Remember that NEAT is the number of calories you burn per day for movement outside of exercise (e.g., chewing and fidgeting). NEAT can vary significantly between people ranging anywhere from 100-800 calories per day. The upper end is probably reserved for tweakers that can’t stop moving.

NEAT is easy to change. Simply standing up for a few hours every day can burn around 170 calories. You can also fidget, change position, and move more. By doing so, you could burn up to 350 extra calories a day.

How to Rev up Your Metabolic Engine

There you go. You’ve now got ways to increase your metabolism that target resting metabolic rate, digestion of food, and your activity levels outside of exercise. These are simple things you can do that help burn more daily calories without breaking a sweat.

Here are some ideas to put these into practice:

Do Something—Anything!

Don’t just consume information. If you’ve read this far, I’m assuming you find this post useful. You’ve now got two choices: 1) close the screen and think ‘that’s nice’ and move on with your day. Or 2) pick one of the above ways to rev up your metabolism and test drive it. Start with one change at a time. Make it so small you can’t fail. And as Nike says, just do it! Decision creates action. Action creates results.

I Need Your Help


You can also share some love by adding a comment below. Let me know which test you’re going to try to rev up your metabolism.

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