What Does Most of Our Energy Expenditure Come From?

November 19, 2025 •

4 min read

Over 60% of daily energy expenditure is used for essential bodily functions while at rest, a process known as the Basal Metabolic Rate (BMR). This means that the majority of energy expenditure comes from keeping the body's fundamental systems running, rather than from exercise or digestion.

Quick Summary

Most daily energy is used for the basal metabolic rate (BMR), the calories burned at rest for essential bodily functions. The remaining energy is spent on physical activity and the thermic effect of food (TEF), with BMR typically accounting for 60-70% of total energy expenditure.

Key Points

Basal Metabolic Rate (BMR) is the main energy expenditure: The body uses 60-70% of its daily energy just to keep vital organs functioning at rest.
Physical activity is highly variable: Energy spent on movement, from exercise to fidgeting, can account for 15-50% of total energy expenditure, and is the most controllable factor.
Digestion burns energy: The thermic effect of food (TEF) uses 5-10% of energy to process and store nutrients.
Muscle boosts BMR: A higher proportion of muscle mass increases BMR because muscle is more metabolically active than fat.
Age and gender affect BMR: BMR tends to decrease with age and is generally higher in men than in women due to differences in body composition.
Organs are major energy users: Vital organs like the brain, liver, and kidneys are among the body's biggest energy consumers at rest.
You can increase energy expenditure: Strategies like resistance training to build muscle and increasing daily physical activity can boost total calorie burn.

The Dominant Factor: Basal Metabolic Rate (BMR)

Scientific research shows that the single largest component of daily energy expenditure is the basal metabolic rate, or BMR. BMR is the energy the body uses to perform involuntary, life-sustaining functions while at complete rest, such as breathing, blood circulation, cell production, and body temperature regulation. For most people, BMR accounts for 60–70% of total daily calorie use.

The Body's Internal Power Consumption

The BMR reflects the constant, round-the-clock work the body does just to stay alive. Even while sleeping or lying still, the organs are working hard to keep the body functioning. The brain alone, despite making up only about 2% of total body weight, can consume up to 20% of the body's total energy expenditure at rest. The liver, kidneys, and heart are also highly metabolically active organs that contribute significantly to BMR.

Factors Influencing BMR

Several factors can influence an individual's BMR, meaning it is not the same for everyone. These include:

Body Composition: Muscle tissue is far more metabolically active than fat tissue. A person with a higher percentage of lean muscle mass will have a higher BMR than someone of the same weight with more body fat.
Age: BMR generally decreases with age. This is often linked to the natural loss of muscle mass that occurs over time.
Gender: Men typically have a higher BMR than women, largely due to their generally higher muscle mass and lower body fat percentage.
Genetics: Metabolic rate can be partly determined by genes.
Body Size: Larger bodies have more metabolizing tissue, which results in a higher BMR.

The Two Other Components of Daily Energy Expenditure

While BMR is the largest piece of the puzzle, two other factors make up the remainder of total energy expenditure.

1. The Thermic Effect of Food (TEF)

TEF, also known as dietary-induced thermogenesis, is the energy the body uses to digest, absorb, and process the nutrients in the food eaten. This process accounts for about 5–10% of total energy use. The energy expenditure for TEF varies depending on the macronutrient composition of the meal:

Protein: Has the highest thermic effect (20-30% of its usable energy).
Carbohydrates: Have a medium thermic effect (5-10%).
Fats: Have the lowest thermic effect (0-3%).

2. Physical Activity

The most variable component of energy expenditure is physical activity. This includes not only planned exercise but also all incidental movement, like walking, fidgeting, and doing household chores. This component can range from as little as 15% in sedentary individuals to as much as 50% in highly active individuals, making it the most significant area for personal control. The total energy spent on physical activity depends on the intensity, duration, and frequency of movement.

Comparison: Energy Expenditure Components


Component	Average Contribution to Total Energy Expenditure	Description	Personal Control
Basal Metabolic Rate (BMR)	60–70%	Energy for fundamental bodily functions at rest (breathing, circulation, etc.).	Low to Moderate (influenced by muscle mass).
Thermic Effect of Food (TEF)	5–10%	Energy used to digest, absorb, and metabolize food.	Low to Moderate (influenced by food type).
Physical Activity	15–50% (Highly variable)	Energy used for any body movement, from walking to vigorous exercise.	High (most significant area for personal control).

How to Influence Energy Expenditure

Understanding the components of energy expenditure allows for more informed strategies regarding weight management. While BMR is largely determined by factors like age, gender, and genetics, you can increase it by building lean muscle mass. Muscle tissue is more metabolically active, burning more calories at rest than fat tissue. This is why incorporating strength or resistance training into a routine is so effective for long-term metabolic health.

Similarly, increasing daily physical activity—especially through high-intensity interval training (HIIT) or regular cardio—is a direct way to boost energy burn. Even making small changes, like standing more or taking more steps throughout the day, contributes to non-exercise activity thermogenesis (NEAT), which can have a significant cumulative effect.

Conclusion

In summary, most energy expenditure comes from the Basal Metabolic Rate, the calories the body burns to keep vital functions running while at rest. This silent but constant work accounts for the largest portion of daily energy use, far surpassing the energy used for digestion or physical activity for the average person. While BMR is influenced by factors beyond control, building muscle mass and increasing overall physical activity are powerful strategies for increasing total energy expenditure and supporting weight management goals. Making mindful choices about activity level and diet allows control of the most variable components of metabolism.

For more detailed information on total daily energy expenditure and related factors, consider exploring the National Institutes of Health website.

Frequently Asked Questions

The largest factor of energy expenditure for most people is the Basal Metabolic Rate (BMR), which is the energy the body uses to perform basic, life-sustaining functions while at complete rest. It accounts for 60–70% of total daily energy use.

No, for the average person, exercise and other physical activity do not use the majority of daily energy. The largest portion is consistently attributed to the Basal Metabolic Rate (BMR), the energy needed for basic bodily functions.

The thermic effect of food (TEF) is the energy required to digest, absorb, and metabolize the food eaten. It accounts for approximately 5–10% of total daily energy expenditure.

Yes, BMR can be increased primarily by increasing lean muscle mass through strength and resistance training. Muscle tissue is more metabolically active and burns more calories at rest than fat tissue.

At rest, the brain is one of the most significant energy consumers. It can use up to 20% of total daily energy, despite making up only a small fraction of body weight.

Energy expenditure, particularly BMR, is affected by both age and gender. BMR tends to decrease with age due to muscle mass loss. Men generally have a higher BMR than women because they have a higher proportion of muscle mass.

NEAT stands for Non-Exercise Activity Thermogenesis, which is the energy expended for everything that is not sleeping, eating, or sports-like exercise. It includes activities like walking, typing, and fidgeting, and contributes to the physical activity component of energy expenditure.