What is BMR (Basal Metabolic Rate)?

What is BMR (Basal Metabolic Rate)?

In theory, it seems so simple: the way to ensure weight loss  is to expend more calories than you consume. But how do we know how many calories your body needs and how can we determine the appropriate calorie level that will allow weight loss to occur for YOU, as an individual?  Everyone is different, and what may be an appropriate calorie level for one person may not work for someone else.  To determine where to start, we first calculate your Basal Metabolic Rate (BMR).

What is your BMR?

Your BMR is a measurement of the energy your body needs to support its basic functions while resting.  The “official” definition requires certain criteria to be met, such as being in a fasting state, in an environment with a controlled temperature, and in relaxed physical and psychological state.  Since that is not always possible, we will just keep it simple and call it the baseline number of calories your body requires to function at rest.

What factors affect BMR?

As always, nothing about weight loss is as simple as it seems.  Your Basal Metabolic Rate is not simply based on your body size or weight, it is also affected by other factors.  Some of these factors are listed below.

AGE
In general, the younger you are, the higher your BMR will be.  As we get older our BMR’s slow down with each decade.  This means we have to change our food strategies (adjusting our calories, and our balance of protein and carbohydrate), and adjust our exercise/activity as we get older, to compensate and succeed.  Hormone changes such as loss of estrogen or testosterone can also slow BMR, and we have strategies to address that.

GENETICS
Individuals may be born with genetic tendencies to have ‘faster’ or ‘slower’ metabolisms, and two otherwise identical people might have metabolisms that vary by 30%, simply because of genetics!  So-called ‘thrifty genes’ which slow metabolic rate, may have been inherited and switched on at some point in our development.  This may have been a great advantage for ancestors who faced food shortages, but can be a challenge in the modern world. People with thrifty genes may require targeted, specific food strategies in order to achieve and maintain a healthy weight.   

There is a whole new field known as ‘epigenetics’ which studies the effects the environment can have on our genes.  Our genes can be affected by what was happening in our mother’s bodies even before we were born (if our mothers were either overweight OR underweight, or were diabetic during pregancy, we might be at higher risk of weight gain due to epigenetic effects.)   Although we can’t change what happened before we were born, we CAN  compensate for it, and set up our future environment and lifestyle to help us succeed.   

PRIOR WEIGHT HISTORY / WEIGHT LOSS
They say “once we buy a fat cell, we own the fat cell” - in other words, when we  lose weight, our bodies may ‘fight it’ and  try  to regain back to our previous weight, by slowing down our BMR.

To illustrate what this means, if you have two people who both weigh 200 pounds, are the same age, the same sex, the same body fat, and otherwise identical, but person A used to weigh 300 pounds, and person B has never weighed more than 200 pounds, person A is going to have a lower BMR (a slower metabolism) than person B.  Not fair, and this can be frustrating, but we need to account for it, and plan for this, in order to succeed.  Specific food strategies and exercise/activity patterns can help combat this problem.

Another effect from prior weight loss attempts is possible  excess loss of muscle, due to poor diet strategies (and inadequate protein).  When people cut too much protein, they lose muscle, and lower BMR - NOT a good idea!  We will help you maintain proper protein intake to avoid this trap.   We can help you REBUILD your muscle - and your metabolism.  We can help you get the proper PROTEIN, at the proper times, along with proper calories for your needs. Studies suggest that two diets with the same calories, may have VERY different metabolic effects: the higher protein versus lower protein diets may increase the 'calorie burn' but 300 calories or more per day! Same calories "in", and extra 300 calories "out" - pretty impressive. People also feel less hungry on diets which have adequate protein.  

One more concern of many is a prior history of ‘yo-yo dieting’.  The bad news is that extremely low calorie diets can slow down BMR excessively.  The GOOD news is that we can FIX this problem with restoration of healthy eating and exercise patterns!  Don’t worry, you didn’t “break yourself” permanently!  

LIFESTYLE
Stress, and poor sleep quality/quantity can slow down or lower your BMR.  Both issues can affect multiple hormones, and end up not only lowering your metabolism, but also increasing your hunger and cravings.

SLEEP
Working on ‘sleep hygiene’ to improve your sleep quality:  keep your room cool, dark, and quiet (or use ‘white noise’ for background, such as a fan or ‘wave machine’).  Before bed avoid caffeine, fatty foods (which can lead to acid reflux), alcohol (which blocks REM sleep), excess exercise (which can trigger insomnia in some people), emotional conflict, and blue light from electronic screens.  Aim for 7 good hours of sleep.

STRESS
Unmanaged stress can lead to lower BMR, and studies have shown that short term stress can measurably slow metabolism!  Long term stress can lead to ‘burn out’ and exhaustion which can lower BMR (and lower our willpower and ability to cope and make good decisions for ourselves).  Many people use meditation (or ‘walking meditation’, also called ‘forest bathing’ by the Japanese, walking outdoors in nature) to help relax, and many use other strategies such as talking to a friend, getting support from a counselor, tai chi or yoga, or engaging in enjoyable hobbies such as music, reading, art, knitting, etc, to help relax.  It is important for us to try to meet needs in our life for relaxation, down-time, creativity, spirituality, healthy socializing - even healthy ALONE time, doing nothing at all sometimes!  

MEDICAL CONDITIONS
Health issues may lower our metabolism, such as pre-diabetes, diabetes, sleep apnea, depression, hypothyroidism, Vitamin D deficiency,  chronic pain, Cushing’s syndrome, and more.  It is important to identify and treat any conditions which may be lowering our BMR.  We commonly identify medical problems which have been either previously undiagnosed, or inadequately treated, which are slowing down metabolic rate.  

MEDICATIONS
There are many medications which can cause your metabolism to be slower, and lead to weight gain.  Common categories of medications which are culprits include over-the-counter antihistamines such as Benadryl/diphenhydramine (a common ingredient in over-slow sleep pills), and certain prescription medications for depression, high blood pressure, diabetes, and more.  We are often able to help patients switch to medications which work as well (or better) for medical conditions, but do not slow down metabolic rate.  

GENDER
Males generally have a higher BMR (faster metabolism) than females, for several reasons.  First, men tend to be larger on average than women, which means their bodies burn more calories, just to stay alive.  Second,  men tend to have more muscle mass, and higher muscle percentage, than women (even women of the same height and weight) -  and muscle ‘burns’ extra calories even at rest when we’re not exercising.  It is important to understand that men and women generally need different calorie levels for weight loss.

Both men AND women can build muscle - and improve BMR and insulin function - with proper diet and exercise strategies.

How do we calculate BMR?

There are various ways to do this,  from low-tech mathematical formulas, to high-tech devices.  In our office we use a method called Bioelectrical Impedance Analysis (BIA) to measure body fat percentage, muscle mass, and water, and the computer uses this information along with your height, age, and sex to provide a good estimate of BMR.  (Biolectric impedence sends a tiny electrical signal from one side of your body to the other,  and is able to estimate your body fat percentage by the speed the signal is transmitted, since the signal is transmitted at different speeds through muscle and fat.)  This method gives a good scientific estimate of BMR, but is not 100% accurate, since your individual genetics, medical history, stress level, and past weight and dieting history may also affect your current BMR.  Nevertheless, it is a great starting point in helping us establish a calorie range for you, to help you achieve your weight loss goals.   If you are not achieving the weight goals we planned, at a given calorie range, it may be a sign that your individual BMR is lower than predicted,  and we can adjust the calories at your next visit.  

Other ways to estimate BMR - Mathematical equations:

Harris-Benedict Equation

This equation uses your height, weight, age to determine BMR.

Men: BMR= 66.5 + (13.8 x weight in kg) + (5.0 x height in cm) - (6.8  x age in years)

Women: BMR= 655.1 + (9.1 x weight in kg) + (1.8 x height in cm) - (4.7 x age in years)

This can then be multiplied by “activity factors” to determine your calorie needs.

Note: this equation often overestimates BMR - see below for a different equation.

Mifflin-St. Jeor Equation

This equation also uses your height, weight, and age to determine BMR, however has been determined to be slightly more accurate than the Harris-Benedict Equation.

Men: BMR= (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5

Women: BMR= (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161

Katch-McArdle Formula

This equation takes into consideration your lean body mass (LBM) and body fat percentage.  It is the same for both men and women.

BMR= 21.6 x fat-free mass + 370

Fat-free mass = Weight - (body fat percentage x weight)

The good news is that our Bioelectric Impedence Device does the calculating FOR you, so you don’t have to!

There are other devices which measure BMR, but are cumbersome.  One is called direct calorimetry, which would be virtually impossible to do!  This involves putting you in an insulated chamber and measuring your body heat.  Not very practical!  Another method is called indirect calorimetry.  This involves hooking you up to a machine and measuring your inhaled oxygen, exhaled carbon dioxide, and excreted urinary nitrogen.  Again, time-consuming and not very practical, and unnecessary!  Our BIA device, plus followup consults, will give us all the information we need!

Learn more about our program at healthyweightcenter.com, and give us a ring if you'd like some help. That's what we're here for! (603) 379-6500. We now offer phone nutrition support, as well, and virtual nutrition visits, if you can't make it in to see us in person.

Today's blog was a team effort by Amy Buzzell, Cara Gourgoumis, and Dr. Jennifer Warren. Learn more about them here: http://www.physicianshealthyweightcenter.com/about_us