Basal Metabolic Rate vs Resting Metabolic Rate
Some experts use the terms basal metabolic rate (BMR) and resting metabolic rate (RMR) interchangeably. These two terms are very similar. But there is a slight difference in the definition of BMR and the definition of RMR that is helpful to understand.
Resting metabolic rate is a measurement of the number of calories that your body burns at rest. Resting metabolic rate is usually measured in the morning before you eat or exercise and after a full night of restful sleep.
Basal metabolic rate (BMR) is a measurement of the number of calories needed to perform your body’s most basic (basal) functions, like breathing, circulation and cell production. This includes processes such as:
- Keeping their brain functioning
- Moving blood throughout the body
- Keeping the heart beating
- Taking oxygen in through the lungs
- Ensuring the kidneys are working, filtering water and waste materials
- Keeping their liver running at full capacity
- Making sure any necessary tissues are being repaired and replaced
- Maintaining contraction of all smooth muscle tissues (which are the tissues of the heart and organs)
BMR accounts for all non-motion-related activities and is the largest contributor of the total daily calorie burn, accounting for about 60-75% of total daily energy expenditure.
The most important factor that influences the BMR value is the total level of lean muscle mass tissue. Muscle is very metabolically active, meaning it burns a high amount of energy on a daily basis, simply sustaining itself. Therefore, someone who has a great degree of lean muscle mass will typically experience a higher overall BMR than someone who does not have as much lean muscle mass.
This is also why men tend to be able to eat more than women without worrying about weight gain. As men tend to have more lean muscle mass in general (thanks to the hormone, testosterone, they have in their body), this helps elevate their resting metabolic rate. Therefore the biggest determining factor over your BMR value is your total level of muscle mass (bodyweight).
Factors That Influence BMR
There are other factors that can influence BMR values as well. These include:
An individual who suffers any type of injury (this could be a sports-related injury or an injury such as a burn or broken bone), their resting metabolic rate will rise. Their body will be working to repair those cells and tissues related to the injury and while doing so, will be utilizing more energy on a day-to-day basis.
It is just the luck of the draw on whether one has a good genetic card or not. Some individuals have a naturally fast metabolism and are naturally thin. These are known as “ectomorphs”. Others who have a slow or sluggish metabolism and have a very low daily calorie burn known as “endomorphs” have a preponderance of body fat. Unfortunately, you cannot change your genetic foundation. The good news is that you can do things to move your natural tendency in a better direction.
If your client had been following a very low calorie (especially a low carb) diet, for an extended period of time, this tends to slow down their resting metabolic rate. The human body adapts to fewer calories consumed and downgrades how much energy it is burning off on a daily basis.
Exercise Selection and Frequency
Exercise selection and frequency are two additional factors that can dictate the metabolic rate your client experiences on a daily basis. If they are performing intense physical training (i.e. sprint training or weight lifting), they can elevate their resting metabolic rate for up to 48 hours after the activity is over. Therefore they are boosting their RMR. Doing this three or more times per week, spread over the course of the day, may in fact lead to a permanently higher metabolic rate as long as this pattern is continued.
The last thing that can influence resting metabolic rate is the climate in which your client lives. Colder climates tend to increase metabolic rates as the body uses more energy to keep the body warm. Keep in mind that this difference is quite minimal and generally does not need to be of concern.
Many people often believe that age is a big factor driving metabolic rate. It has been heard people complain that since they are getting older, ‘their metabolism just isn’t what it used to be.’ Often they are stating this as an excuse as to why they cannot lose weight (or why they have gained so much weight in the first place). Note that it usually is not the actual increase in age causing the metabolic rate to slow down, but more, the fact that over the years, they have become less active and this has led to the loss of lean muscle mass tissue.
As muscle mass tissue is lost, that is what then causes the metabolic rate to slow down.
Researchers have discovered that starting between the ages of 25 and 30, most people begin losing 5-10 pounds of lean muscle for each decade of life that follows, illustrating just how powerful this concept really is. Remember it’s never too late to begin a proper strength training program. Put the effort in now and you will be looking better because of it in the years to come. In this regard, it’s very possible to sustain a higher metabolic rate as one age provided they are performing proper strength training exercises to keep their muscle levels up.
As can be seen, an individual’s BMR is influenced by a few different things. This can account for the differences from one individual to the next. Generally speaking, if there are two individuals of the same weight and body composition level, they will have relatively the same RMR values.
One study published in the American Journal of Clinical Nutrition noted that generally speaking, only 2% of the observed variability in BMR values across individuals was due to factors unrelated to fat-free mass levels. Fat-free mass is the driving factor determining your BMR value.
How to Measure Your BMR
If you are looking to reach or maintain a healthy weight may find it helpful to calculate your BMR. You can either find the number using a formula designed by scientists, you can get it tested in a lab, or you can use an online calculator. No method is perfectly accurate, but a lab test will probably give you the best estimate.
But since lab tests can be costly, many dieters and exercisers use one of the other two methods to determine basal metabolic rate and/or the total number of calories they burn each day.
The equation to Calculate Your BMR
The Harris-Benedict Equation is often used to estimate basal metabolic rate.
- Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)
- Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)
Learning about your basal metabolic rate and the total number of calories you burn each day is a positive step in the process of reaching or maintaining a healthy weight. The more you know, the easier it is to make changes in your life that produce real results.
Track your numbers, keep a weight loss journal, gather support from your trainer or coach, friends and family, and connect with your healthcare team to find a plan that works over the long-term for you.
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