What Does Resting Energy Include?

December 17, 2025 •

5 min read

Accounting for 60-75% of your total daily calorie expenditure, resting energy expenditure (REE) is the energy your body uses for basic survival functions while completely at rest. So, what does resting energy include beyond just breathing and circulation?

Quick Summary

Resting energy includes the calories used for vital organ function, cellular repair, and basic physiological processes. It is influenced by body composition, age, and genetics.

Key Points

Vital Organ Function: Resting energy is primarily used to fuel high-metabolic-rate organs like the liver, brain, heart, and kidneys, which consume a large percentage of calories despite their small size.
Lean Body Mass Impact: The amount of lean body mass (muscle) you have is the strongest predictor of your resting energy expenditure, as muscle tissue is more metabolically active than fat.
REE vs. BMR: While often used interchangeably, Resting Energy Expenditure (REE) is slightly higher than Basal Metabolic Rate (BMR) because it is measured under less stringent conditions.
Age and Gender Factors: Age and gender influence resting energy levels, with metabolism typically slowing with age and men generally having a higher REE due to greater lean muscle mass.
Larger Energy Picture: Resting energy is just one component of Total Daily Energy Expenditure (TDEE), which also includes the energy for physical activity (both exercise and NEAT) and the thermic effect of food.

The Core Components of Resting Energy Expenditure (REE)

Resting energy expenditure (REE), also commonly referred to as Resting Metabolic Rate (RMR), is the total energy your body consumes to maintain basic functions while in a state of rest. This is the energy required simply to stay alive, performing a myriad of internal tasks. The REE measurement typically occurs in a less restrictive setting than BMR, reflecting the body's energy usage after an overnight fast. This energy supports fundamental processes that keep you functioning smoothly every second of the day.

The Body's Non-Stop Functions

At the most basic level, resting energy powers the essential physiological systems that sustain life. This includes:

Breathing: The continuous contraction and relaxation of your diaphragm and other respiratory muscles to inhale oxygen and exhale carbon dioxide.
Blood Circulation: The tireless work of your heart to pump blood throughout your body, delivering nutrients and oxygen to cells and removing waste.
Body Temperature Regulation: The process of maintaining a stable internal body temperature, a function that requires a significant amount of energy.
Cellular Growth and Repair: The ongoing regeneration and maintenance of cells and tissues throughout your body.
Brain and Nerve Function: The brain, despite its relatively small size, is a major consumer of resting energy due to its high metabolic demand for neural activity.
Organ Activity: The normal functioning of all vital organs, such as the liver, kidneys, and spleen.

The High-Metabolic-Rate Organs

While skeletal muscle makes up a significant portion of body weight, it is actually the high-metabolic-rate organs (HMROs) that account for the bulk of resting energy expenditure. The liver, brain, heart, and kidneys, despite comprising less than 6% of total body weight, collectively contribute to roughly 60–70% of REE. The liver, in particular, accounts for a substantial portion of this, around 20-30%, due to its role in processing nutrients and maintaining metabolic balance. The brain's continuous neural activity also makes it a major energy consumer at rest. Variations in the size and metabolic rate of these organs can significantly impact an individual's total REE.

The Role of Lean Body Mass

Lean body mass (LBM), which includes muscle, bone, and organs, is the strongest predictor of an individual's REE. This is because muscle tissue is significantly more metabolically active at rest than fat tissue, burning approximately three times more calories per pound. Individuals with a higher percentage of lean muscle mass will have a higher resting energy expenditure, as more calories are required to fuel and maintain that muscle tissue. This is why increasing muscle mass through strength training can be an effective long-term strategy for boosting metabolism. Conversely, a loss of lean body mass, often associated with aging or prolonged underfeeding, leads to a decrease in REE.

Resting Energy (REE) vs. Basal Metabolic Rate (BMR)

The terms Resting Energy Expenditure (REE) and Basal Metabolic Rate (BMR) are often used interchangeably, but there are subtle technical differences. Understanding these distinctions is important for grasping the nuances of metabolism.


Criterion	Resting Energy Expenditure (REE)	Basal Metabolic Rate (BMR)
Definition	Energy expended at rest in a post-absorptive state.	Minimum energy needed to keep the body functioning at a basic level.
Measurement Conditions	Less restrictive; measured at any time of day after an overnight fast.	Strict lab conditions; measured in a darkened, quiet, temperature-controlled room after 8 hours of sleep and 12 hours of fasting.
Value	Typically 10-20% higher than BMR.	Lower than REE, representing the absolute minimum energy expenditure.
Common Usage	More practical and commonly used measure for estimating daily calorie needs.	More of a theoretical benchmark for research purposes due to strict conditions.

Key Factors That Influence Your Resting Energy

While the basic components of REE remain constant, several factors can influence your individual metabolic rate. The precise value of your REE can be affected by a complex interplay of biological and environmental influences.

Age: Resting metabolism generally declines with age, largely due to a decrease in lean body mass.
Sex: Men tend to have a higher REE than women, primarily because they typically have a greater proportion of lean muscle mass.
Body Size and Composition: Individuals with larger bodies or more lean muscle mass have a higher REE, as it takes more energy to sustain a larger frame.
Genetics: An individual's metabolic rate is influenced by their genetic makeup.
Hormonal Health: Hormones, particularly those from the thyroid gland, play a significant role in regulating metabolic rate. Imbalances can lead to a slower or faster metabolism.
Environmental Temperature: The body expends energy to maintain a stable internal temperature in response to very low or very high environmental temperatures.
Nutritional Status: Periods of caloric restriction can cause a metabolic adaptation, lowering REE in an effort to conserve energy.

Conclusion: The Bigger Picture of Your Energy Burn

Understanding what resting energy includes is fundamental to understanding your body's total energy expenditure. As the largest component of your daily calorie burn, REE powers the vital, non-stop functions that keep you alive, from the high-metabolic demand of your brain and liver to the baseline needs of every cell. However, REE is just one piece of the puzzle. Your Total Daily Energy Expenditure (TDEE) also includes the Thermic Effect of Food (TEF) and the energy burned through physical activity, both voluntary exercise and Non-Exercise Activity Thermogenesis (NEAT). By recognizing the factors that influence your REE, like body composition and age, you can better appreciate how your body manages energy and make more informed decisions about your overall health and wellness. For more detailed information on energy expenditure, authoritative sources like the NCBI Bookshelf offer in-depth resources, such as Control of Energy Expenditure in Humans.

Sources

National Institutes of Health (NIH) | (.gov) - Control of Energy Expenditure in Humans - Endotext - NCBI Bookshelf - https://www.ncbi.nlm.nih.gov/books/NBK278963/ National Institutes of Health (NIH) | (.gov) - Energy - Recommended Dietary Allowances - NCBI Bookshelf - https://www.ncbi.nlm.nih.gov/books/NBK234938/ National Institutes of Health (NIH) | (.gov) - Brain and high metabolic rate organ mass: contributions to... - https://pmc.ncbi.nlm.nih.gov/articles/PMC2844678/

Frequently Asked Questions

REE is the energy your body burns at rest, measured under relatively less strict conditions, while BMR is the minimum energy needed for vital functions, measured under very controlled laboratory conditions after a long fast and a full night's sleep. REE is typically 10-20% higher than BMR.

Vital organs like the liver, brain, heart, and kidneys consume the majority of resting energy, accounting for 60-70% of the total, despite making up a small fraction of body weight. Basic functions such as breathing, blood circulation, and cellular repair are also included.

The most effective way to increase your resting energy is to build more lean muscle mass through regular strength training. Since muscle is more metabolically active than fat, having more muscle tissue will cause your body to burn more calories at rest.

Yes, age affects your resting energy. As people get older, there is a natural decline in metabolism, often associated with a loss of lean body mass. This means older adults typically have lower resting energy needs than younger adults.

Body composition, particularly the ratio of lean muscle mass to fat mass, strongly influences resting energy. Individuals with more lean mass will have a higher REE, while a higher proportion of fat mass is associated with a lower REE.

Yes, resting energy is only one part of your Total Daily Energy Expenditure (TDEE). The other main components are the Thermic Effect of Food (TEF), the energy used for digestion, and the energy from physical activity, which includes both planned exercise and non-exercise activity thermogenesis (NEAT).

While direct measurement requires specialized equipment like indirect calorimetry, you can estimate your REE using predictive equations such as the Mifflin-St Jeor or Harris-Benedict formulas. Many online calculators use these equations.