Resting Energy Expenditure may not be something you have heard a lot about. Let’s dig in and find out what it’s all about.

Amidst all the complicated explanations behind weight-loss strategies, have you ever wondered if there is a simple principle behind weight loss or weight gain?

Well… there is.

Why Do You Need to Know About Resting Energy Expenditure?

The reasons why we have controlled diets, workout sessions and choose certain foods over others have all got to do with two processes that embody one basic concept – Energy Intake < Energy Expenditure. I.e. Energy intake should be less than energy expenditure.

On the one hand, we reduce our energy intake and on the other, we increase our energy expenditure. Basically, it means eat less, work more. This is the fundamental principle behind weight loss or weight gain.

It is for the increased Energy Expenditure process that we perform exercises or calorie-burning activities.

To many of us who have struggled with weight loss or weight gain at some point in our lives, we must have realized that the majority of energy expenditure does not happen when we exercise. In fact, it is a continuous process and there is a very common word used to describe this – “Metabolism”.

We must have heard that a certain person has a slow metabolism and therefore, has trouble losing calories. And inversely, a certain person has a fast metabolism and therefore, has trouble gaining weight.

All of this is tied to one central concept – the Basal Metabolic Rate (BMR).

For practical purposes, you may think about it as synonymous to the aforementioned “metabolism”. BMR is, in turn, directly related to the Resting Energy Expenditure (REE) – the tendency of a human body to burn calories at rest.

In fact, 60-75% of your daily calorie expenditure is via this process and it ultimately decides whether you maintain, gain, or lose weight. So suffice to say that it ties directly with all our efforts for weight loss or weight gain.

But partial-knowledge about some topics (esp. health-related) can be more dangerous than ignorance.  The truth is that it will be worth it for you to have a good understanding of this topic as it is a vital part in daily energy expenditure. It definitely helped me out.

This is also the underlying concept behind most weight loss/gain practices that are advocated by many. Knowing how this works will give you more clarity about how it can help you with your fitness goals and tweak any related practices that you feel is necessary.

Basic Metabolic Rate vs. Resting Metabolic Rate

Basal metabolic rate (BMR)

This is the rate of energy expenditure per unit time by endothermic animals at rest. Endothermic animals are those that can regulate the heat of their body using their internal bodily functions. Humans are endothermic.

It can also be defined as the amount of energy per unit time required by a person to keep the body functioning at rest.

This includes the energy required to maintain the vital processes for living like respiration, blood circulation, cell growth, controlling and maintaining body temperature, brain and nerve function, breathing, and muscle contraction.

Resting metabolic rate (RMR)

This has a similar definition as BMR. RMR is the amount of energy required to keep your body in perfect homeostasis while resting (including sleeping).

The main difference between BMR and RMR is the time at which the above two are measured. The measurement of BMR is done under very restrictive conditions. The BMR reading is taken immediately upon waking from 8 hours of sleep. This is more like a value in an ideal steady-state and hence, a more scientifically accurate value will be obtained¹ (Wikipedia).

RMR reading is more flexible in the sense that it can be taken when a person is asleep or awake and there is no requirement for 8 hours of sleep. Most other conditions in the measurement of BMR and RMR are same. The RMR can be 10-20% higher than BMR due to the thermic effect. 

Your takeaway needs to be that both BMR and RMR more or less refer to a similar concept and that a layman need not consider a distinction between them for weight control activities.

That being said, BMR is mainly used for scholarly/clinical/scientific purposes.

From a practical standpoint (like weight control), RMR or REE is more useful.

What Is Resting Energy Expenditure (REE)?

In very simple terms, REE is the amount of energy that you burn at rest.

Resting Energy Expenditure (REE) is in direct proportion to Resting metabolic rate (RMR) ¹ (Wikipedia). This means that the more your RMR, the higher will be your REE.

Will Resting Metabolic Rate (RMR) Change With Age And What Does This Mean For You?

Yes. RMR decreases with age.

This is one of the reasons why you are advised to reduce calorie intake as you grow older² (Manini, 2010). The peak of metabolic rate can be somewhere in the teens to the early twenties based on your genetics. It starts slowing down for almost everyone after 30.

How Can You Use Resting Energy Expenditure (REE) to Your Advantage?

Understanding the factors that impact resting energy expenditure can be helpful for weight-loss.

Some of these factors are naturally occurring. Nonetheless, being conscious of them, using them to your advantage whenever possible and planning your diets or workouts based on this knowledge may help you achieve your desired results.

Factors Impacting Resting Energy Expenditure

Below are some factors that affect our Basal Metabolic Rate (BMR) and therefore, our Resting Energy Expenditure (REE):

1. Lean muscle mass

People who tend to work out and build muscles have a higher REE than people with a sedentary lifestyle.

In fact, with regard to REE, it is inferred that anaerobic exercises (like weight lifting) may be more beneficial than aerobic exercises (like cardio workouts) as the former builds more muscle mass which will help in energy expenditure even while resting³ (Wikipedia).

2. Age

Age slows down metabolic rate. Young people in their growth spurts would have a much higher BMR than sedentary adults above 45 years of age.

Also, loss of lean muscle happens as you age. This is called Sarcopenia with Aging. This also factors into the reduced metabolism along with ageing.

3. Temperature

When it is cold, our metabolism has to expend energy to maintain body temperature. This leads to more calories being burned for even normal activities.

Inversely, when it is hot, the metabolism has to do work to lower the body temperature.

4. Gender

Generally speaking, men have more muscle mass than women. So men tend to have a higher metabolic rate than women.

5. Disease

If you are down with a fever, your metabolic rate will be higher. This is a common pathological cause for a temporary increase in the metabolic rate.

With a rise of your temperature in every Fahrenheit, the BMR increases by 7%.

6. Injury

If you are injured or had a surgery, the acuteness of the wound will correspondingly raise your metabolic rate as part of the healing process^{4, 5} (Murray, Sharecare; Şimşek et al., 2014).

This is just your body spending more energy to heal the wound.

7. Pregnancy

This is a no-brainer. When you are pregnant, you feed (at least) two people (yourself and the child). This considerably increases your BMR.

8. Lactation

Lactating mothers can expend a considerable amount of calories (about – 500-1000) per day via lactation. This, naturally, gives a major boost to your BMR⁶ (Wikipedia).

9. Body frame

Tall, thin people and people with bigger frames tend to have more BMR than the others who have smaller/shorter frames even if they have the same weight.

This is mainly because of the increase in skin area of the former through which more heat is lost via radiation.

10. Hydration

Dehydration can decrease the BMR as the body will be trying to conserve energy. Make sure to stay sufficiently hydrated to assist your metabolism.

Read our article on the 37 Benefits of Drinking Water to learn more about the importance of hydration.

11. Digestion

The digestive process accelerates BMR.

Small, healthy snacks at regular intervals can boost BMR whereas long periods between meals (especially between meals in which the calorie consumption is below 1000 calories) can slow down BMR.

12. Hormones

The hormones produced by Thyroid gland plays a vital role in BMR.

The main ones that I am talking about here are Triiodothyronine, also known as T3 and Tetraiodothyronine, also called thyroxin or T4.

They make all of the cells in the body to work harder, so the cells need more energy too. This results in an increase in body temperature and faster pulse and a stronger heartbeat.

Food is used up more quickly because energy stored in the liver and muscles is broken down. It also results in the activation of the nervous system. This leads to: improved concentration and faster reflexes; brain maturity and growth promotion in children⁷.

If you are a person with a weight problem (both weight loss or gain), it would be advisable to take a thyroid test to make sure that your thyroid function is normal.

13. Caffeine

Caffeine consumption increases the Resting Energy Expenditure.

A study⁸ (Acheson et al., 1980) had shown that metabolic rate increased significantly during the 3 hours after caffeine ingestion.

14. Fasting/Starvation

Going into hunger mode will slow down your metabolism as the body tries to ration energy for vital bodily functions⁹ (Debruyne et al., 2007).  

Now, this should not be taken to mean that fasting does not help with weight loss. It just means that being hungry can slow down your resting energy expenditure. And that may not be a problem if your calorie intake is less in the first place.

15. Stress

Stress increases the metabolic rate. But this doesn’t mean that stress can help you lose weight or is good for your health.

In fact, stress increases your appetite and leads to weight gain¹⁰ (McEwen et al., 2006).

16. Sleep

Sleep slows down metabolism or resting energy expenditure. This is temporary and confined to the time you are asleep.

17. Green tea

Resting Energy Expenditure increases by the consumption of Green tea¹¹ (Chacko et al., 2010).

Green tea has many other health benefits as well.

18. Smoking

Smoking increases your metabolic rate.

Studies have shown that subjects who quit smoking started gaining weight with the same lifestyle^9,12 (McEwen et al., 2006; McGovern et al., 2011).

That’s it, folks!

You may keep this in mind when you plan for diets or decide to opt for a certain weight-loss program. It will certainly benefit you, in the long run, to know how these factors are affecting you and what the intensity of that impact will be.