Metabolism 101: Everything You Need to Know About How Your Body Burns Calories

WHAT IS METABOLISM?

Metabolism is often treated like a buzzword or a convenient scapegoat when progress stalls. But it's more than a “fast” or “slow” setting on our bodies -- it’s a set of chemical processes that keeps us alive, digesting, moving, and adapting.

The Cambridge definition of metabolism is: all the chemical processes in our bodies, especially those that cause food to be used for energy and growth.

Understanding metabolism gives us insight into what actually affects our energy needs, what might be slowing us down, and where we can take action. We’re going to break down the components of metabolism, what impacts them, and how to work with your body—not against it.

By the end, you’ll be able to answer:

• Is my metabolism actually slow?

• Can I do anything to speed up my metabolism?

Let’s walk through the four components of metabolism, what influences each one, and how to make them work to your advantage.

Is My Metabolism Slow?

When people say they have a “fast” metabolism, they’re usually talking about someone who seems to burn through calories and stay lean with ease. A “slow” metabolism, on the other hand, is often blamed for easy fat gain or stalled progress.

But technically, a fast metabolism doesn’t burn calories faster — it burns more calories overall. Imagine a car: the car that burns the most fuel doesn’t necessarily drive faster, it just covers more distance. That’s how metabolism works.

The Four Components Of Total Daily Energy Expenditure (Tdee)

TDEE is the total number of calories we burn each day. It has four parts:

• Basal Metabolic Rate (BMR) / Resting Metabolic Rate (RMR)

• Non-Exercise Activity Thermogenesis (NEAT)

• Thermic Effect of Food (TEF)

• Exercise Activity Thermogenesis (EAT)

Each of these contributes differently to your total calorie burn. Let’s break them down.

Basal Metabolic Rate (Bmr): Your Baseline Calorie Burn

BMR is the amount of energy your body uses just to keep you alive — breathing, circulating blood, digesting, regulating temperature. It’s the biggest chunk of your daily calorie burn, usually between 40 and 80% of TDEE.

Note: BMR and RMR are often used interchangeably, though technically different. RMR includes low-effort daily activities like eating or using the bathroom. For simplicity, we’ll use BMR throughout the rest of this post.

What affects BMR?

Factors we can’t change:

• Genetics. We each have a genetic set point for metabolic rate. While we can influence metabolism, we’re still working within our genetic range.

Factors we can influence:

• Lean muscle mass. This is by far the most significant factor we can change. More muscle = more calories burned at rest. To build muscle, focus on eating enough calories, getting adequate protein, and strength training regularly.

• Sleep. Good-quality, consistent sleep supports a healthy BMR and preserves muscle mass. Poor sleep does the opposite.

• Chronic energy intake. Your body adjusts to consistent intake. Chronically under-eating can cause your BMR to drop. A well-planned, periodized nutrition strategy can help support a higher BMR.

Small contributors:

• Supplements. Some supplements may have a very modest effect on BMR. Caffeine and fish oil show the most promise. Certain spices like chili, ginger, and turmeric may have a tiny impact, but don’t expect miracles here.

How do we boost our metabolism in regards to BMR?

• Lift weights and build muscle,

• Practice good sleep habits,

• Follow a good periodized nutrition plan,

• While supplements are pretty overrated, a few of them (fish oil and caffeine mainly) may slightly boost our metabolism.

Thermic Effect Of Food (Tef): Calories Burned From Eating

TEF is quite simply the energy (or heat) our body creates in response to breaking down and digesting food. When we consume food, our bodies expend calories to process it, including digestion, absorption, and assimilation of nutrients. This caloric expenditure contributes to our overall metabolism. TEF typically accounts for approximately 8% to 15% of our Total Daily Energy Expenditure (TDEE).

What factors affect TEF?

Macronutrient composition:

• Protein has the highest thermal effect, ranging from 15% to 30% of the calories consumed. This means that if we eat 100 calories of protein, we might burn 15 to 30 calories just digesting it, leaving a net of 70–85 calories for the body.

• Carbohydrates have a moderate thermal effect, usually between 5% and 10%, with simpler carbs being closer to 5% and complex fibrous carbs being closer to 10%. So, 100 calories of carbohydrates might result in a net of 90–95 calories after digestion.

• Fat has the lowest thermal effect, typically between 0% and 2%. This means nearly all the calories from fat are absorbed and assimilated, making it a highly efficient energy source.

Food quality:

Calories in vs. calories out (CICO) is always the #1 factor in weight loss, but the TEF effect shows how the makeup of food affects CICO. For example, a study showed that an 800-calorie meal had a TEF of about 10% for highly processed food, but a TEF of 20% for less processed whole food—meaning more calories were burned digesting the whole food version.

How do we boost our metabolism in regards to TEF?

• Prioritize a diet composed mostly of whole foods.

  • A good rule of thumb - eat 14 grams of fiber per 1000 calories consumed.

• Increase the percentage of calories we consume from protein while potentially reducing calories from carbohydrates or fats to maintain overall caloric intake.

  • For example, someone eating 40% protein will burn significantly more calories through TEF than someone at 10% protein, even if their total caloric intake is the same.

• This is more a side benefit of the first two tips and not something we specifically do, but a typical high-protein diet composed of mostly whole foods increases satiety and can spontaneously lead to a reduced overall caloric intake.

Non-Exercise Activity Thermogenesis (Neat): Your Hidden Calorie Burn

NEAT refers to all the physical activity we do throughout the day that is not structured, specific exercise. This includes a wide range of activities such as fidgeting, walking, pacing, taking the stairs, etc. NEAT can account for a significant portion of our TDEE—typically ranging from 5% to 30%. In fact, for many people, NEAT can contribute as much, if not more, to their total energy expenditure than structured exercise.

Another cool thing about NEAT is that it’s highly responsive and the most modifiable component of TDEE, meaning NEAT may be the area where we can MOST “boost” our metabolism (boosting our metabolism simply means burning more overall calories).

Here are some practical ways to increase NEAT

• Standing Desks – A standing desk can burn an additional 100 to 200 calories per day, depending on factors like duration and body weight. It's not necessary to stand all day; alternating between standing and sitting can still contribute positively.

• Treadmill Desks – Walking at a very low speed (e.g., 1 mile per hour) while working, especially during meetings or non-typing tasks, can burn an additional 50–100 calories per hour, accumulating substantially over time.

• Walking – If you don’t want to shell out for a walking or standing desk, maybe you can walk for free outside? Frequent, short walks throughout the day can significantly increase NEAT. For example, taking three 10-minute walks per day can easily add a few hundred calories to your daily expenditure.

• General Movement – Take the stairs, walk around during phone calls, pace instead of sitting, park farther away from the entrance - these all contribute to higher NEAT.

How do we boost our metabolism in regards to NEAT?

The short answer is to move more, but an intervention that is actually shown to increase NEAT is to measure our daily step count.

Set a realistic goal to increase your daily movement. For example - If on average you take 6,000 steps a day, increase your steps to 8,000 a day.

Exercise Activity Thermogenesis (Eat): Calories Burned From Workouts

EAT is the calories burned during planned exercise. For most people, it contributes 10 to 20% of total energy expenditure (though for athletes, it can be much higher).

How different types of exercise affect EAT:

• Strength training builds muscle (which supports BMR) but doesn’t burn as many calories in the session itself

• High-intensity interval training (HIIT) leads to some post-exercise calorie burn (EPOC), though it’s often overestimated—typically around 30 to 50 additional calories

• Steady-state cardio burns the most calories per session, especially when sustained over longer durations

How to support metabolism through EAT:

• Exercise regularly and consistently

• Include cardio if calorie burn is a priority

• Increase exercise duration or intensity over time

CAN YOU ACTUALLY SPEED UP YOUR METABOLISM?

So is your metabolism slow? Look, it is what it is largely because of genetics, but it's not broken or stuck that way! We can boost our metabolism. Here are the big rocks we can move to make a difference, summarized:

QUICK RECAP: HOW TO SUPPORT A HEALTHY METABOLISM

• Build muscle through strength training and a structured nutrition plan

• Get enough sleep with good habits around rest and recovery

• Eat enough protein (0.7 to 1.0 grams per pound of body weight)

• Choose mostly whole foods and aim for 14 grams of fiber per 1000 calories

• Increase daily movement and step count gradually

• Exercise consistently, including cardio for calorie burn and strength for long-term support

None of this is flashy. But these habits, done consistently, will help you get the most from your metabolism.

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