What Does Resting Energy Requirement Mean for Your Body's Needs?

November 30, 2025 •

4 min read

Resting energy requirement (RER) accounts for the largest portion of your total daily energy expenditure, typically 60-70%. This fundamental metric represents the energy your body needs to perform essential functions while at rest, serving as a critical baseline for understanding nutritional demands. The concept can be used for both humans and pets, with slight variations in its precise application.

Quick Summary

Resting energy requirement (RER) is the amount of energy the body needs to sustain vital functions while at rest. It is a key component of total daily energy expenditure, influenced by factors like age, gender, and body composition. Knowing your RER is crucial for accurate weight management and overall health planning.

Key Points

Baseline Caloric Needs: Resting energy requirement (RER) is the minimum energy your body needs to perform essential functions at rest, such as breathing and blood circulation.
Largest Energy Component: RER makes up the largest part of your total daily energy expenditure, typically 60-70%.
RER vs. BMR: RER (Resting Energy Expenditure) is a practical, less restrictive measurement than Basal Metabolic Rate (BMR), though the terms are often used interchangeably in practice.
Influential Factors: RER is affected by body composition (lean mass increases RER), age (declines with age), sex, genetics, hormones, and climate.
Weight Management: Knowing your RER is crucial for setting appropriate calorie goals for weight loss, gain, or maintenance. It serves as a baseline to ensure you don't under-eat.
Practical Calculation: RER can be estimated using formulas like the Mifflin-St Jeor equation, which incorporates weight, height, age, and sex.
Species Differences: While the concept applies to both humans and animals, specific formulas and application contexts differ for pets based on their metabolic needs and body size.

Understanding Resting Energy Requirement (RER)

Resting energy requirement (RER), also known as resting energy expenditure (REE) or resting metabolic rate (RMR), is a vital concept in nutrition and health science. It quantifies the energy your body uses to sustain its most fundamental life-supporting processes when you are awake, but completely at rest. These processes include breathing, blood circulation, maintaining body temperature, and basic neurological functions. The RER is a significant part of your body's total daily energy needs and provides a foundational number for any dietary plan or weight management goal.

RER vs. BMR: What's the Difference?

While the terms RER and basal metabolic rate (BMR) are often used interchangeably, there is a technical difference. BMR is a more precise, restrictive measurement, typically taken in a highly controlled, laboratory setting after a 12-hour fast and a night of sleep. RER, on the other hand, is measured under slightly less stringent conditions, such as after sitting or lying down quietly for about 15 minutes. For practical purposes in most nutritional planning, the two values are close enough to be considered equivalent. RER tends to be slightly higher than BMR because it includes the minor energy expenditure from low-effort daily activities.

How to Calculate Your Resting Energy Requirement

To estimate your RER, several empirically derived equations are available. The Mifflin-St Jeor equation is one of the most widely used and is considered more accurate than older formulas.

Mifflin-St Jeor Equation for RER

For Men: $RER = (10 \times weight{kg}) + (6.25 \times height{cm}) - (5 \times age) + 5$
For Women: $RER = (10 \times weight{kg}) + (6.25 \times height{cm}) - (5 \times age) - 161$

These equations provide a good starting point for estimating your daily energy needs. Once you have your RER, you can multiply it by an activity factor to determine your total daily energy expenditure (TDEE), which gives a more complete picture of your total caloric needs.

Factors That Influence Resting Energy Requirement

Your RER is not a static number; it is influenced by a range of factors that can cause it to vary significantly between individuals. Some factors are fixed, while others can be managed through lifestyle choices.

Key Influencing Factors:

Body Composition: Lean body mass, which includes muscles and organs, is much more metabolically active than fat mass. People with more muscle mass generally have a higher RER.
Age: RER naturally decreases with age, primarily due to a gradual reduction in lean body mass.
Sex: Men typically have a higher RER than women due to having a greater proportion of muscle mass and different hormonal profiles.
Genetics: Genetic makeup can influence metabolic rates, meaning that some individuals are naturally predisposed to burn more calories at rest than others with similar body composition.
Hormones: The thyroid gland is a major regulator of metabolism. Hormonal imbalances, such as those seen in thyroid dysfunction, can significantly impact RER.
Fever: Illnesses that cause a fever will temporarily increase RER as the body expends more energy to raise its temperature.
Climate: The body burns more energy to maintain its core temperature in colder environments, increasing RER.

How RER is Used in Weight Management

Understanding your RER is the foundation of any informed weight management plan. It is a reliable indicator of the minimum calories your body needs to function.

Weight Loss: To lose weight, you must create a calorie deficit, meaning you burn more calories than you consume. Knowing your RER helps determine your maintenance calories, and you can subtract from this number to create a safe deficit. It is important not to restrict calories below your RER, as this can negatively impact health and metabolic function.
Weight Gain: To gain weight, a calorie surplus is needed. Calculating your RER is the first step to determining your maintenance calories, which can then be increased to promote weight gain effectively.
Maintenance: For weight maintenance, the goal is to balance your calorie intake with your total daily energy expenditure (TDEE), which is built upon your RER.

RER for Human vs. Pet Nutrition

While the underlying concept of RER is the same for humans and pets, the formulas and application differ significantly based on species-specific metabolic rates.


Feature	Human RER	Pet (Dog/Cat) RER
Primary Calculation Method	Mifflin-St Jeor or Harris-Benedict equations using height, weight, age, and gender	Specialized formulas, often based on body weight raised to a power (e.g., kg^0.75)
Measurement Accuracy	Equations provide estimates, with accuracy varying based on individual factors like body composition and genetics.	Formulas provide estimates that can have high individual variability (up to 50%), so they serve as starting points.
Key Factors	Age, gender, lean body mass, hormone levels, genetics.	Body weight, life-stage (e.g., puppy/kitten vs. adult), reproductive status, activity level.
Application	Serves as a baseline for dietary and fitness planning for weight management and overall health.	Used by veterinary professionals to determine initial feeding guidelines for proper nutritional support.

Conclusion

Understanding what does resting energy requirement mean is fundamental to grasping your body's most basic energy needs. RER represents the significant portion of your metabolism that powers essential functions even while you are sedentary. By learning how to estimate your RER and identifying the factors that influence it, you gain a powerful tool for making informed decisions about your nutrition, fitness, and weight management goals. For both personal and professional applications, from human dietary planning to veterinary nutritional support, RER provides the critical baseline required for effective energy management.

Visit a resource for further reading on metabolic rates.

Frequently Asked Questions

RER, or Resting Energy Requirement, is the energy burned at rest under less restrictive conditions. BMR, or Basal Metabolic Rate, is a more precise measurement taken after a longer period of complete rest and fasting in a controlled setting. For practical purposes, they are often used interchangeably, with RER being slightly higher due to minor low-effort activities.

RER decreases with age primarily due to a natural, age-related decline in lean body mass, particularly muscle tissue. Since lean mass is more metabolically active than fat, its reduction leads to a lower overall resting energy expenditure.

Yes, you can increase your RER mainly by increasing your lean body mass through strength training. Muscle tissue burns more calories at rest than fat tissue, so building muscle will raise your resting metabolic rate over time.

For weight loss, your RER is used as a baseline. To lose weight, you must consume fewer calories than your total daily energy expenditure (TDEE). Knowing your RER helps you establish a safe caloric deficit without cutting calories too low, which can harm your health.

Factors such as recent meals (thermic effect of food), activity levels (post-exercise energy expenditure), sleep, illness (fever), and environmental temperature can cause minor fluctuations in your RER from day to day.

Yes, men generally have a higher RER than women. This difference is largely due to men typically having a greater proportion of lean muscle mass, which has a higher metabolic rate than body fat.

Predictive equations for RER, like the Mifflin-St Jeor formula, provide good estimates but are not perfectly accurate for every individual. Factors like genetics and individual body composition mean that there can be significant person-to-person variation. For the most accurate measurement, indirect calorimetry is used in a clinical setting.