How many calories do you burn sleeping? Calculator

Editor: John Ajayi, B.Sc, MBA
Medical review: Moyo Adeyemi, M.B., B.S., FRCPC
Science Editor: Sunday O. Ajayi, Ph.D
How many calories you burn while sleeping depends on many factors. Pic credit: Pixabay

If you’ve been wondering how many calories you burn while sleeping and how to calculate the energy cost of nightly rest, we have all the answers to your questions.

While you’ve probably already guessed that you burn fewer calories while sleeping, you may also want to know how to calculate or estimate your overnight energy expenditure as part of your weight loss calculations.

We present a Calories Burned Calculator (click the link to view our calculator) that estimates your rate of energy expenditure while sleeping. The calculator takes multiple factors — such as age, sex, height, and weight — into account when calculating the following:

  • Sleeping Metabolic Rate (SMR)
  • Resting Metabolic Rate (RMR)
  • Resting rate of oxygen consumption

We also cover everything you need to know about how to calculate energy expenditure while sleeping yourself. We show you the different methods you can use to calculate your Sleeping Metabolic Rate (SMR) and compare it with Basal Metabolic Rate (BMR) based on the findings of research studies.

Calculating calories burned while sleeping is easy. It does not require advanced math skills.

Contents:

Calories Burned Calculator: Get an estimate of your sleeping metabolic rate

How to interprete values returned by our calculator

How many calories do you burn while sleeping?

How to calculate calories burned while sleeping

Calories burned sleeping: Harris-Benedict formula

Calories burned sleeping: Metabolic Equivalent of Task (MET)

What is the Metabolic Equivalent of Task?

Corrected MET values

Calculate Sleeping Metabolic Rate using standard MET value

Other contents:

Sleeping Metabolic Rate vs Basal Metabolic Rate (BMR)

Are calories burned while sleeping equal to Basal Metabolic Rate?

Does REM sleep burn more calories than non-REM?

Factors that affect calories burned while sleeping

Calories Burned Calculator: Get an estimate of your Sleeping Metabolic Rate

You can use our Calories Burned Calculator (below) to estimate how many calories you burn while sleeping. Simply enter your age, sex, body weight, height, and sleep duration, and our calculator does the math for you.

However, if you want to learn how to do the calculation yourself, this article walks you through various easy-to-use methods.

How to inteprete values returned by our calculator

You will notice that the calculator lists two estimates of the calories you burn while sleeping. The first is based on the MET value of sleep and the second is your Resting Metabolic Rate (RMR) as predicted by the Harris-Benedict equation based on your age, sex, weight, and height.

The following information about how age and sleep quality affect Sleeping Metabolic Rate (SMR) may help you guess which of the two values (MET value-based or RMR-based) is likely the best predictor of your SMR:

Research studies suggest that younger individuals and older ones who enjoy a high sleep quality may have average Overnight (sleeping) Metabolic Rates (OMR) roughly equal to their Resting Metabolic Rate (RMR).

Young people who enjoy a high sleep quality may be more likely than older people to have an average overnight SMR significantly lower than their RMR.

Some studies suggest that Sleeping Metabolic Rate (SMR) may be up to 5% lower than RMR in some healthy and lean individuals who enjoy a high sleep quality (Goldberg and associates (1988).

However, studies also show that most individuals experience a degree of age-related decrease in sleep quality. The decrease in sleep quality is associated with a higher-than-expected Overnight Metabolic Rate (OMR).

Thus, your SMR is likely higher than your predicted RMR if you are middle-aged or older (>40). How much higher will depend on your sleep quality. The lower your sleep quality the more likely that your SMR will be significantly higher than your predicted RMR.

You probably enjoy a high sleep quality if you sleep undisturbed through the night, feel refreshed in the morning, and your bedsheets aren’t crumpled.

You likely suffer from poor sleep quality if your sleep is fragmented, you toss and turn all night, and your bedsheets are disordered in the morning.

We shall discuss the research-based evidence in detail later in this article.

How many calories do you burn while sleeping at night?

The average 40-year-old adult American woman, standing 63.5 inches (161 cm) tall and weighing 170.8lbs (78kg) (according to CDC’s average height and weight stats for Americans), burns 63-78 calories per hour while sleeping at night.

The average 40-year-old adult American man, standing 69 inches (175cm) and weighing 200 pounds (91kg), burns between 80-91 calories per hour sleeping.

These estimates are based on values predicted by the Harris-Benedict equation and values derived from the Standard MET values of sleeping. Overnight metabolic rate also depends on sleep quality.

Read on the learn how to use the Harris-Benedict equation and Standard MET values to predict Sleeping Metabolic Rate (SMR). You will also learn more about factors, such as sleep quality, that affect SMR.

How to calculate calories burned while sleeping

Calories burned while sleeping can be measured using indirect calorimeter. Pic credit: Pixabay

The most accurate way to determine calories burned while sleeping (Sleeping Metabolic Rate, SMR) is through measurement using various methods such as:

  • Direct and indirect calorimetry
  • Doubly labeled water technique (DLW)
  • Heart rate monitoring
  • Accelerometry

The indirect calorimetry method is one of the most widely used for measuring Basal Metabolic Rate (BMR) and may also be used to measure Sleeping Metabolic Rate (SMR).

However, if you are unable to measure your SMR using calorimetry, DLW, or accelerometry, you may estimate it by first calculating your BMR.

You may calculate your BMR using any of the following three formulas:

Note that these formulas can only give a rough estimate of your BMR. While they account for factors such as body weight, height, age, and sex (the Katch-McArdle Formula also factors in lean mass), they don’t take account of other relevant factors, such as race or ethnicity, hormonal factors, health status, and diet.

Seale and Conway (1999) reported that Sleeping Metabolic Rate (SMR) was equal to Basal Metabolic Rate (BMR). Thus, BMR likely offers an estimate of Sleeping Metabolic Rate (SMR) that may be adequate for most people trying to find their weight loss or weight loss maintenance calories.

However, Goldberg and associates (1988) reported that average SMR was lower than BMR by 5%. But they concluded that the difference was negligible when applied over 24 hours to calculate energy expenditure values expressed as calories/day.

Calories burned sleeping: Harris-Benedict formula

You can calculate the calories you burned while sleeping using various formulas. Pic credit: Pixabay

Example:

Calculate the Sleeping Metabolic Rate (SMR) for a 20-year-old female, 5 feet 7 inches tall (170.18cm), weighing 132 pounds (60kg).

Step 1: Calculate the subject’s BMR (per day)

The Harris-Benedict formula for women: BMR = 655 + ( 9.563 × wt in kg ) + ( 1.850 × ht in cm ) – ( 4.676 × age in years )

BMR = 655 + (9.563 X 60) + (1.850 X 170.18) – (4.676 X 20)

BMR = 655 + 573.780 + 314.833 -(93.520)

BMR = 1543.613 – (93.520) = 1450.093 calories/day

Step 2: Calculate BMR per hour

Divide 1450.093 calories/day by 24 hours = 60.421 calories per hour

Seale and Conway (1999) reported that BMR was equal to SMR. Thus, we may conclude that the subject burns 60.421 calories per hour while sleeping.

Sleep experts recommend that adults get 7 to 8 hours of nightly rest, while teenagers should get 8 to 10 hours. Thus, if the subject slept 8 hours overnight, the total calories burned while sleeping:

60.421 calories x 8 hours = 483.368 calories

Step 3: If you prefer a conservative estimate of SMR, you may follow the recommendation by Goldberg and colleagues (1988) that the rate of energy expenditure while sleeping was 5% less than BMR.

Thus (as per Goldberg et al.), multiplying BMR per hour by 0.95 gives an estimate of calories burned per hour while sleeping:

60.421 x 0.95 = 57.40 calories/hour while sleeping

Calories burned overnight (8 hours of sleep):

57.40 calories x 8 hours = 459.20 calories

Calories burned sleeping: Metabolic Equivalent of Task (MET)

Calculating calories burned while sleeping is easy. It does not require advanced math skills. Pic credit: Pixabay

You can also calculate the calories you burn while sleeping using a formula that incorporates a factor representing the Metabolic Equivalent of sleeping.

What is the Metabolic Equivalent of Task (MET)?

The metabolic equivalent of any task (MET) is a ratio that compares the rate at which you expend energy while performing that task to a reference task.

The most commonly used reference is the rate at which you burn calories while sitting quietly (Resting Metabolic Rate, RMR).

The reference task (sitting quietly) is assigned a MET value of 1, and other tasks are assigned a MET value that compares the metabolic rates associated with those tasks with the reference task.

For instance, doing bodyweight squats vigorously is assigned a MET value of 8. That means that an average person performing bodyweights squats expends 8 times the energy she expends while sitting quietly.

Performing sit-ups with moderate effort is assigned a MET value of 3.8, meaning and average person performing sit-ups expends 3.8 times the energy she expends while sitting quietly.

Similarly, vigorous push-ups have a MET value of 8.0, while light push-ups have a MET value of 2.8.

MET is thus a ratio or index that measures the intensity of any physical activity relative to sitting quietly.

One MET is formally defined as the rate of oxygen consumption while sitting quietly. It is equivalent to 3.5 milliliters of oxygen consumed per kilogram body weight per minute (3.5ml/kg/min).

The energy equivalent of 3.5ml/kg/min is 1 kcal/kg/hr.

However, the MET standard is only an estimate set by convention. It was based on the resting oxygen consumption of a healthy 40-year-old male, weighing 70kg (Byrne et al., 2005).

Not everyone consumes exactly 3.5 milliliters of oxygen per kilogram body weight per minute while sitting quietly. Many people have lower rates of resting oxygen consumption, while others have higher rates, depending on factors, such as age, gender, and lean mass.

In a previous article, we discussed how to burn more calories while sitting. We reviewed multiple studies that showed that even modest physical activity while sitting, such as leg movements and chair-based fidgeting, can significantly increase sitting metabolic rates.

Experts use the rate of oxygen consumption to measure the rate of energy expenditure because your cells use oxygen to break down glucose and release energy during the process called cellular respiration. Thus, your rate of oxygen consumption is positively correlated with the rate at which you burn calories.

You breathe in oxygen from the atmosphere through your nose into your lungs. The oxygen passes through the thin tissues of your alveoli in the lungs into your bloodstream.

Your bloodstream then distributes the oxygen to tissue and organ cells, where it reacts with glucose derived from the food you eat.

The reaction breaks down glucose to release carbon dioxide, water, and energy. You use the energy released to fuel biological functions and breathe out the carbon dioxide and water.

Corrected MET values

Several researchers have attempted to adjust for inaccuracies when MET values are calculated for different individuals using the 3.5ml/kg/min standard without correcting for factors such as age, sex, height, and weight.

MET values calculated using the 3.5ml/kg/min standard without correcting for age, sex, height, and weight are referred to as Standard MET values.

Kozey and associates (2010) reported that using 3.5 ml/kg/min to calculate MET often overestimates RMR and thus underestimates MET values. Researchers proposed correcting for age, sex, height, and weight by using measured RMR or dividing standard MET (3.5 ml/kg/min) by the Resting Metabolic Rate (RMR) value predicted by the Harris-Benedict formula.

The Harris-Benedict formula helps derive corrected MET values because it accounts for individual age, height, weight, and gender/sex differences (Byrne et al., 2005).

Corrected MET value = Standard MET value x 3.5/RMR predicted by Harris-Benedict equation (ml/kg/min)

Calculate corrected MET value

Example:

Calculate the corrected MET value of sleep for a 20-year-old female, 5 feet 7 inches tall (170.18cm), weighing 132 pounds (60kg).

Corrected MET value = Standard MET value x 3.5/RMR predicted by Harris-Benedict equation (ml/kg/min)

[Note: We previously calculated the predicted RMR for the subject as 1450.093 kcal/day kcal/day using the Harris-Benedict equation.]

Step 1. We first convert RMR expressed as kcal/day to RMR expressed as ml/kg/min (see conversion rates here):

Step 1(a). Convert 1450.093 kcal/day to kcal/min equivalent:

1450.093/1440 = 1.007009 kcal/min

Step 1(b): Convert kcal/min to L/min:

1.007009/5 = 0.201402 L/min

Step 1(c): Convert L/min to ml/kg/min:

0.201402/60 x1000 = 3.3567 ml/kg/min

The subject’s predicted resting oxygen consumption after correcting for her age, weight, height, and sex = 3.3567 ml/kg/min (approximately 3.4 ml/kg/min).

Step 2: Calculate the corrected MET value of sleep:

Corrected MET value of sleep = 0.95 x 3.5/3.4 = 0.9779 MET (or 0.98MET)

The corrected MET value of sleep is thus approximately 1, meaning that our young subject’s SMR is roughly equal to her RMR (Seale and Conway (1999).

However, we’d likely get different results with older subjects because the Harris-Benedict equation yields significantly lower values of RMR for older people. In other words, older people tend to have a higher MET value of sleep than young adults and teenagers.

A higher MET value of sleep is also consistent with research studies suggesting many older people have a higher-than-expected Sleeping Metabolic Rate associated with decreased sleep quality (Valenti et al. (2017)).

Calculate Sleeping Metabolic Rate using standard MET value

An average female burns about 50 calories per hour while sleeping overnight. Pic credit: Pixabay

Example:

Calculate the Sleeping Metabolic Rate (SMR) of a 20-year-old female, 5 feet 7 inches tall (170.18cm), weighing 132 pounds (60kg) using the standard MET value.

According to the Compendium of Physical Activities, the standard MET value for sleeping is 0.95.

SMR= Standard MET x 3.5 ml/kg/min x (weight in kilograms)/200

SMR= 0.95 x 3.5 x (60)/200 = 0.9975 cal/min = 59.85 calories per hour

Calories burned sleeping 8 hours = 59.85 x 8 = 478.8 calories

Below are estimated MET values for some activities (Mendes et al., 2018):

Lying down: 1.0 (±0.2)

Sitting: 1.3 (±0.3)

Standing: 1.2 (±0.3)

Slow walking (3km/h): 3.0 (±0.6)

Brisk walking (6km/h): 5.4 (±1.0)

Running (8km/h): 8.2 (±1.1)

Kozey and associates (2010) reported the following METs measured using a portable metabolic system and an accelerometer:

Ascend stairs (16 story building): 10.3

Descending stairs: 4.4

Washing dishes: 2.1

Gardening: 4.0

Mowing: 5.9

Raking: 4.7

Basketball (Shooting baskets): 9.3

Sleeping Metabolic Rate vs Basal Metabolic Rate (BMR)

Some studies suggest that sleeping metabolic rate is higher thann BMR. Pic credit: Pixabay

Sleeping Metabolic Rate (SMR), or Overnight Metabolic Rate (OMR), refers to calories burned while sleeping.

Sleeping Metabolic Rate (SMR) is similar to Basal Metabolic Rate (BMR) because both consist mainly of energy expenditure required to sustain essential bodily functions, such as blood circulation, digestion, body temperature regulation, respiration, tissue repair, and brain metabolism.

However, some studies reported a significant difference between the number of calories burned while sleeping (SMR) and Basal Metabolic Rate (BMR). Other studies reported no significant difference between both.

We shall review the studies and the conflicting results after we have defined the relevant terms:

Sleeping Metabolic Rate (SMR) is the rate at which you burn calories while sleeping.

Basal Metabolic Rate (BMR) is the rate at which your burn calories while awake but resting (reclined) in a thermal neutral zone at least 12 hours after your last meal.

A thermal neutral zone is the range of environmental temperatures in which an average healthy person can maintain a normal range of body temperatures without the need to expend energy above BMR.

Researchers measure BMR in a clinical setting under carefully controlled conditions.

BMR is preferably measured in the morning after the subject has fasted for 12 hours, rested overnight (8 hours), and refrained from vigorous physical activity for up to 24 hours.

The subject should have avoided taking stimulants, including nicotine and alcohol, for 12 hours.

Resting Metabolic Rate (RMR), also known as Resting Energy Expenditure (REE), is usually measured as a close approximation of BMR.

Are calories burned while sleeping equal to Basal Metabolic Rate?

Zhang and associates (2002) measured calories burned while sleeping (Sleep Metabolic Rate, SMR), Total Daily Energy Expenditure (TDEE), and Resting Metabolic Rate (RMR) in 18 healthy, pre-menopausal, obese, and non-obese female subjects (6 Caucasians and 12 African-Americans).

Their ages ranged from 22 years to 45 years.

They took the measurements using a human respiratory chamber.

They reported that SMR decreased continuously during sleep and reached its lowest level in the early hours before the subject awakened in the morning.

They also reported that Sleeping Metabolic Rate (SMR) tended to be significantly higher than Resting Metabolic Rate (RMR) at the beginning of the sleep period. But it decreased during the night until it fell to a minimum below RMR in the early hours before waking.

According to the researchers, the rate of decrease of SMR after the beginning of the sleep period increased with increasing body weight and body mass index (BMI). Thus, while averages of SMR and RMR were “similar,” average SMR “tended” to be lower than RMR in obese subjects but higher than RMR in non-obese subjects.

Seale and Conway (1999) measured Overnight Energy Expenditure and BMR of 69 adult subjects in a room-sized indirect calorimeter. They reported that although energy expenditure dropped significantly below BMR during sleep, Overnight Energy Expenditure and BMR (expressed as megajoules/day) were equal.

According to the researchers, energy expenditure dropped significantly below BMR for about 60 minutes during sleep. However, Overnight Energy Expenditure was equal to BMR.

Seale and Conway’s conclusion that SMR and BMR were equal appeared to conflict with Zhang and associates, who reported that average SMR was higher than BMR in non-obese subjects but lower in obese subjects.

Goldberg and associates (1988) conducted a study to assess FAO and WHO energy requirement recommendations that assumed the energy cost of sleep (SMR) was equal to Basal Metabolic Rate (BMR).

They used whole-body indirect calorimetry to measure Overnight Metabolic Rate (OMR/SMR) and BMR in 80 healthy subjects, including 40 “normal lean” subjects.

The researchers found that the mean ratio of OMR and BMR in “normal lean subjects” was 0.95, indicating that Sleeping Metabolic Rate (SMR) was lower than Basal Metabolic Rate (BMR) by about 5% in lean subjects.

They also reported that the mean ratio of the lowest SMR and BMR was 0.88, meaning that SMR continued to drop during the night while the subjects slept until it was lower than BMR by about 12%.

Goldberg and colleagues concluded that their study suggested that assumptions that overnight energy expenditure (or overnight MR) was equal to BMR may lead to an average overestimation of SMR by approximately 5%.

However, the overestimation was negligible when estimating 24-hour BMR or TDEE.

The conclusion by Goldberg and colleagues appeared to contradict Zhang and associates, who reported that average SMR “tended” to be higher than RMR in non-obese subjects.

It also appeared to contradict Seal and Conway, who reported that average SMR was equal to BMR.

While it may require expert review and further research studies to explain the apparent differences between the results obtained by the three research teams, we may note the following differences in methodology:

  • Seale and Conway reported measuring BMR. Goldberg and associates also reported they measured BMR. However, Zhang and associates said they measured RMR. RMR, as we previously explained, is only an approximation of BMR, and there may be significant differences between the two depending on how the measurements were taken.
  • The study by Seale and Conway involved 69 adults of different genders, ages, weights, and heights but the race and ethnicity of the participants were not known. Goldberg and associates also didn’t specify the race/ethnicity of the participants in their study. However, Zhang and associates reported that 12 of the 18 subjects who participated in their study were African Americans. Some studies suggested that people of Black African descent may have lower BMRs or RMRs than people of caucasian descent (Gannon et al., 2000, Spaeth et al., 2015)

Does REM sleep burn more calories than non-REM?

REM sleeping (dream sleep) burns more calories than non-REM sleep. Pic credit: Unsplash

Multiple studies confirmed that metabolic rate decreased during sleep and reached its lowest level in the early hours before the subject awakened in the morning.

The decrease in energy expenditure during sleep occurs as the subject moves through the different stages of the sleep cycle.

Fontvieille and associates (1994) noted that changes in SMR during sleep were due to different rates of energy expenditure (EE) associated with the different sleep stages.

The researchers conducted a study to assess the relationship between EE and sleep stages. The study involved 29 subjets of different ethnicities (Caucasians and Pima Indians), gender (male and female), age, sex, and weight. Fontvieille and associates used electroencephalographic (EEG) readings to determine sleep stages and measured EE using indirect calorimetry.

The authors reported that SMR was related to sleep stages. Metabolic rates decreased as subjects progressed through the three stages of non-REM sleep, but peaked during REM sleep (stage 4).

However, the differences in energy expenditure (EE) between the sleep stages were not enough to account for differences in SMR between the subjects. The researchers reported that the differences in SMR between the subjects were due to differences in fat-free mass (FFM), fat mass, age, sex, and ethnicity.

Brebbia and Altshuler (1965) earlier reported significant differences in energy expenditure (EE) between the four stages of sleep, with REM sleep having the highest EE. Energy expenditure (EE) decreased as subjects progressed through the non-REM sleep stages (stage I — stage 2 — stage 3).

Sleep experts (Patel et al., 2021) recognize four stages of the sleep cycle based mainly on eye movements, muscle movements, and electroencephalographic (EEG) features (brainwave frequencies and amplitudes).

The four stages are:

1. Non-REM sleep consists of Stage 1 (lightest sleep), Stage 2 (deeper sleep), and Stage 3 (deepest sleep)

2. REM sleep (Stage 4) is characterized by dreaming, EEG that resembles wake time, and loss of skeletal muscle tone (atonic).

However, some experts split Stage 3 sleep into two stages (3 & 4) and thus recognize five stages of sleep.

A normal healthy sleep cycle progress through stages non-Rem stages 1, 2, 3, and 4, and finally REM (stage 5).

The progressive decrease in BMR as a healthy sleeper passes through the stages of non-REM sleep occurs because the body resets its temperature regulation at a lower level. The resulting drop in temperature is associated with lower metabolic rates since less energy (measured in calories) is needed to maintain the lower set temperature. Lower body temperatures are also associated with lower respiratory rates.

Factors that affect calories burned while sleeping

1. Age

Fast-grow infants, children, and adolescents have higher metabolic rates than adults. Thus, we’d expect infants and young children to have higher sleeping metabolic rates than adults.

According to Pontzer and associates (2021), fat-free mass-adjusted energy expenditure accelerates rapidly in neonates (newborns) to about 50% above adult levels in the first year of life. It declines slowly to adult levels at about 20 years and remains stable until about 60 years.

Although Pontzer and colleagues found that fat-free mass-adjusted energy expenditure was stable in middle-aged adults, other studies suggested that total energy expenditure decreases due to a decrease in fat-free mass.

Thus, metabolic rates tend to drop as we age (Schrack et al., 2000; McMurray et al., 2014). Middle-aged (40-60) and older adults (>60 years) have lower total metabolic rates than younger people.

According to Lazzer and colleagues (2010), data suggested that age-related decline in BMR was due to a reduction in lean mass (see also Alley et al., 2008) or fat-free mass (FFM).

Valenti and associates (2017) reported that an age-related decrease in sleep quality was associated with an increase in Overnight Metabolic Rate (OMR). In other words, some people experience an age-related increase in Overnight Metabolic Rate associated with decreased sleep quality.

2. Gender or sex

Men have higher basal metabolic rates than women due to multiple factors, including the role of hormones, such as testosterone.

Researchers believe that testosterone promotes leanness and partly explains why men have a higher muscle-to-fat ratio than women (Traish et al., 2014, Fui et al., 2016).

Men burn more calories at rest than women due to having a higher muscle mass percentage. Men also tend to lose weight faster than women (Williams et al., 2014).

3. Body weight

Lee and associates (2017) reported that sleeping energy expenditure was significantly higher in obese than non-obese children (children with high body mass index BMI), but weight-adjusted SEE (sleeping energy expenditure per unit of body weight) was not statistically different.

Zhang et al. (2016) reported that overweight people have a higher BMR than people with normal body weight.

4. Height

Censi and associates (1998) reported that taller people have a lower BMR per unit of body weight than shorter people.

The authors studied two groups of men (Tall vs. Short) with similar body fat percentages. The tall group (T) had a BMR 20% higher than the short group (S). However, when expressed as per unit of body weight and fat-free mass, group T had BMRs 12% and 10% lower than group S.

However, more studies are need to confirm whether lower BMR per unit of body weight for tall people was positively associated with lower SMR.

5. Physical activity level

Studies suggested that sedentary people burn fewer calories than physically active individuals while sleeping. People who engage in more intense physical exercise activity during waking hours have higher metabolic rates throughout the rest of the day, including during sleep.

Westerterp and colleagues (1991) studied the relationship between physical activity (PA) during the day and metabolic rate during sleeping (SMR). They found that Sleeping Metabolic Rate was positively correlated with physical activity.

However, Goldberg and associates (1998) reported that in “normal lean subjects,” the ratios of Overnight MR and BMR were not significantly affected by different levels of exercise during the day. In other words, exercise levels during the day did not significantly increase or decrease SMR in lean subjects.

The result appears to contradict Westerterp and colleagues (1991). More studies may be needed to clarify the relationship between daytime activity and Sleeping Metabolic Rate.

6. Fat-free mass

We previously noted that people with higher lean body mass have a higher metabolic rate than people with a lower lean body mass.

Zhang and associates (2002) conducted a study to determine the relationship between SMR and body weight (BW), body mass index (BMI), and fat-free mass (FFM).

They measured total energy expenditure (TEE), sleeping metabolic rate (SMR), and resting metabolic rate (RMR) in a respiratory chamber.

The researchers found that SMR decreased during sleep and that while it was higher than RMR at the beginning of the sleep period, it decreased until it was lower than RMR in the morning hours. They also reported that the rate of decrease in SMR was positively associated with BW, BMI, and FFM.

In other words, people with high fat-free mass experienced a faster decrease in SMR during sleep.

Zhang and associates also concluded that average SMR was lower than RMR in obese subjects and higher than RMR in non-obese subjects.

7. Genetic factors

Several studies indicate that genetic factors may also play a role in determining metabolic rates. Hellwege and associates (2017) investigated the genetic basis of the differences in RMR between individuals.

They suggested that understanding the genetic determinants of metabolic rates may help us understand the causes of obesity and how it relates to type 2 diabetes and cardiovascular diseases.

Konarzewski and Książek (2013) also reported that genetic factors play a role in metabolism and that there was a need to integrate molecular genetics into the study of intra-species variations in metabolism.

8. Hormonal factors

Many hormones, such as the adipocyte-derived hormone leptin, are involved in regulating metabolism.

Fischer and colleagues (2016) reported that an increase in leptin production promotes weight loss by increasing energy expenditure or thermogenesis and inducing a reduction in food intake (hypophagia).

A decrease in leptin production promotes weight gain by reducing energy expenditure and causing an increase in food intake (hyperphagia).

Bouret (2013) reported that metabolic hormones regulate hypothalamic circuits that control energy homeostasis.

Hormones such as ghrelin, insulin, thyroid hormone, and testosterone play a role in the regulation of metabolism (Mullur et al., 2014, Pradhan et al., 2014, Vargas et al., 2021).

9. Race and ethnicity

Studies have reported variations in metabolic rates between people of different racial and ethnic heritages.

According to some studies, people of Black African descent may have a lower BMR than people of caucasian descent (Spaeth et al., 2015).