What Accounts for the Majority of Energy Expenditure? Your Metabolism Explained

November 19, 2025 •

2 min read

The human body is an engine that constantly burns calories, even at rest. In fact, most of your daily energy is used just to keep you alive and functioning. Understanding what accounts for the majority of energy expenditure is the first step toward effectively managing your weight and improving your metabolic health.

Quick Summary

Total daily energy expenditure is primarily dictated by your basal metabolic rate, which covers essential bodily functions. The remaining energy is spent on physical activity and the processing of food.

Key Points

Basal Metabolic Rate (BMR) Dominates: BMR accounts for the majority of energy expenditure, typically 60-75% of your total daily calories, used for fundamental bodily functions.
Physical Activity is Most Variable: Physical Activity Energy Expenditure (PAEE) is the most variable component of your daily caloric burn, ranging widely based on exercise and daily movement (NEAT).
Muscle Mass Boosts BMR: Because muscle tissue is more metabolically active than fat, having a higher percentage of lean body mass can increase your BMR.
Age Slows Metabolism: As you age, your BMR naturally decreases, mainly due to a loss of muscle mass, which is a key factor in metabolism.
Food Costs Energy to Process: The Thermic Effect of Food (TEF) accounts for about 10% of your daily energy use, with protein requiring more energy to digest than fats or carbs.
NEAT is a Powerful Tool: Non-Exercise Activity Thermogenesis (NEAT), which includes all non-exercise movement like fidgeting or walking, can significantly impact your total daily energy expenditure.
Hormones are Key Regulators: Hormones, particularly those from the thyroid, play a critical role in regulating your metabolism and BMR.

The Three Key Components of Total Daily Energy Expenditure (TDEE)

To understand what accounts for the majority of energy expenditure, it's essential to break down your total daily energy expenditure (TDEE) into its primary components. TDEE is the total number of calories your body burns in a day and is composed of three main parts: Basal Metabolic Rate (BMR), the Thermic Effect of Food (TEF), and Physical Activity Energy Expenditure (PAEE).

Basal Metabolic Rate (BMR): The Largest Contributor

Your BMR, or Basal Metabolic Rate, is the energy your body needs to maintain its basic, life-sustaining functions at complete rest. For most sedentary individuals, BMR accounts for a substantial 60% to 75% of their TDEE.

Several factors can influence your BMR:

Body Composition: Muscle tissue is far more metabolically active than fat tissue. Higher muscle mass generally leads to a higher BMR.
Age: BMR generally decreases with age, primarily due to the natural loss of muscle mass.
Body Size: Larger bodies require more energy. Taller and heavier individuals typically have a higher BMR.
Genetics: Your genetic makeup plays a role in your metabolic rate.
Hormonal Health: Hormones, particularly thyroid hormones, regulate metabolism.

Physical Activity Energy Expenditure (PAEE): The Most Variable Factor

PAEE is the energy you burn through any form of physical movement. This is the most dynamic component of TDEE and can range from 15% in sedentary people to over 50% in highly active individuals.

PAEE includes:

Exercise Activity Thermogenesis (EAT): Energy burned during planned exercise.
Non-Exercise Activity Thermogenesis (NEAT): Energy expended for all movement that is not sleeping, eating, or purposeful exercise, such as walking, cleaning, or fidgeting. NEAT can vary significantly between individuals.

Thermic Effect of Food (TEF): The Energy Cost of Digestion

The final component is the Thermic Effect of Food (TEF), the energy used to digest, absorb, and metabolize food. TEF is relatively stable, about 10% of total daily caloric intake.

The TEF varies by macronutrient:

Protein: Highest thermic effect (20-30%).
Carbohydrates: Moderate thermic effect (5-15%).
Fats: Lowest thermic effect (0-5%).

Comparison of Energy Expenditure Components


Component	Percentage of TDEE	Variability	Primary Function
Basal Metabolic Rate (BMR)	60-75% for sedentary people	Relatively stable (long-term)	Essential life-sustaining functions at rest
Physical Activity Energy Expenditure (PAEE)	15-50% (most variable)	Highly variable (day-to-day)	All physical movement, intentional or not
Thermic Effect of Food (TEF)	~10%	Low variability	Digestion, absorption, and storage of food

Conclusion

In summary, the Basal Metabolic Rate (BMR) accounts for the majority of energy expenditure for most individuals, representing the calories burned for fundamental bodily functions. Physical activity and the thermic effect of food also contribute, but are typically smaller components of total daily energy expenditure. Understanding these components is key for managing weight and optimizing health. The National Center for Biotechnology Information (NCBI) provides extensive research on this topic.

Frequently Asked Questions

The Basal Metabolic Rate (BMR) is the amount of energy your body needs to maintain its most basic, life-sustaining functions while at complete rest. It accounts for the largest portion of your total daily calorie expenditure.

The most effective way to increase your BMR is by building lean muscle mass through strength and resistance training. Muscle tissue burns more calories at rest than fat tissue, boosting your overall metabolism.

The Thermic Effect of Food (TEF) is the energy your body expends to digest, absorb, transport, and store the nutrients you consume. It typically accounts for about 10% of your total daily calorie burn.

Yes, physical activity is the most variable component of your daily energy expenditure. The more you move, from structured exercise to non-exercise activities like walking and fidgeting, the more calories you burn.

For most people, intentional exercise contributes a relatively small, though important, part of their total daily energy expenditure. For highly active individuals, however, it can become a significant portion, sometimes over 50%.

Your metabolism, and specifically your BMR, tends to slow down as you age. This is primarily due to a natural decrease in lean muscle mass over time.

NEAT is the energy expended for all physical activities that are not intentional exercise. This includes walking, gardening, household chores, and even fidgeting, and can account for a significant portion of daily energy burn.