Resting Metabolic Rate
You’ve probably heard of resting metabolic rate many times. But, do you know what it is? How to measure it? How to increase it? And how it burns fat? Well, wonder no more, as we are here to explain it all.
What is resting metabolic rate?
Let’s take it word by word here. Resting means that you are at rest a.k.a. not doing anything. Metabolic refers to metabolism of course. What is metabolism? Metabolism includes all chemical reactions in your body, that are necessary to keep you alive. Three main purposes of metabolism are: converting food to energy, converting food to protein, lipids and other structural elements of your body, and eliminating byproducts of these reactions – nitrogenous wastes. All these processes can be divided in two groups: anabolic (which builds tissue and use energy) and catabolic (which break down tissue and food to get energy). Last word is rate, which is an assigned value, according to a particular scale.
From this analysis we can conclude that resting metabolic rate (RMR) is a measurement of your metabolism while at rest. This means that it measures the energy your body needs to perform basic functions while resting, just to keep you alive.
Don’t confuse resting metabolic rate and basal metabolic rate (BMR). They both measure energy needs while resting. The difference is that basal metabolic rate refers to awake individuals, resting in bed for 24 hours, in ideal condition (e.g. perfect room temperature), so no more than minimal energy is needed. It is mostly used for clinical purposes.
Metabolic rate differs from person to person
We are all individuals. We differ in many things including resting metabolic rate. There are many elements that cause these variations, like:
- Genetics – Of course it is kind of predetermined by genetics. Some people are blessed with faster metabolism, while others are cursed with slower one.
- Gender – Men, on average, have more muscle mass, and lower body-fat percentage than women, meaning they naturally have higher BMR.
- Age – Children have higher BMR than adults. As you get older, your BMR decreases.
- Height – Greater body surface and lean muscle mass mean higher BMR. Simply put – taller people have higher BMR.
- Weight – More weight = higher BMR. Muscles contribute more to the increase of BMR than fat.
- Diet – Very restrictive diets and starvation decrease BMR.
- Body temperature – as chemical reactions are faster at higher temperature, BMR will increase with the body temperature. For every 0.5 degrees C, there will be an increase in BMR by 7%.
- External temperature – The colder it is, more energy your body needs to keep its temperature at wanted levels. Therefore, colder external temperature increases BMR.
- Hormones – Thyroid hormones are the main contributors to BMR. More of these hormones means higher BMR. Too much of this hormones can double BMR and lead to a condition called thyrotoxicosis. Less of these hormones, of course means decreased BMR. Adrenaline can also increase BMR, but not as much as thyroid hormones.
- Exercise – As we mentioned before, more muscle means higher BMR. So workouts that build muscle can increase BMR.
How to calculate resting metabolic rate and basal metabolic rate?
There are few ways to calculate RMR ad BMR. An accurate, but difficult method is calorimetry. It uses expired gases for its calculations. Calorimetry can also determine which food is being used for energy. After measuring oxygen uptake(VO2), and carbon dioxide output(VCO2), Abbreviated Weir Equation can be used to calculate RMR.
RMR = (3.9 (VO2) + 1.1 (VCO2)) x 1.44
Respiratory quotient (RQ) – tells which food is used for energy
RQ = VCO2 / VO2
For fat RQ = 0.7, protein = 0.8. carbohydrate = 1, fat storage >1, ketosis <0.7, mixed energy = 0.85.
More commonly used, simpler, but less accurate are several formulas to determine RMR and BMR. The calculations are for calories/day.
Haris – Benedict equation
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)
Katch – McArdle BMR formula
370 + (21.6 x LBM)
500 + (22 x LBM)
LBM refers to lean body mass. To calculate it you need to know your body fat percentage first. Than subtract it from your weight in kilograms. So if you weigh 90kg, and your body fat percentage is 20 %, your LBM is 90kg – 20% (18kg) = 72kg.
Why should you calculate resting metabolic rate?
First of all knowing your RMR can help you increase it and lose more weight. With RMR you can calculate total daily energy expenditure (TDEE) and find out how much calories is your body using in a day.
TDEE = RMR + TEF + NEAT + EPOC + Ex
TEF – thermogenic effect of food, NEAT – non-exercise activity thermogenesis, EPOC – excess post-exercise oxygen consumption, Ex – exercise.
How to increase resting metabolic rate?
Most of the factors that contribute to metabolic rate are predetermined, you can’t do much there. You want to focus on the ones you can interfere with. I’m not talking about inducing fever, taking thyroid hormones or locking yourself into freezer. These are, well not so smart or effective. Focus on exercises that build muscle. High intensity interval training (HIIT) is currently considered the best option to increase BMR. It raises the heart rate, burns calories during workout and builds muscle. Regular muscle building exercises are also good. Downside is that they don’t burn as much calories as HIIT.
As RMR decreases with age, you want to do everything you can to bring it back up. One study, from 1994. done on healthy 50-65 year old men, shows that 16 week heavy resistance strength training increased RMR by 7.7 %. This results indicate that training increased muscle mass, and thus increased RMR as well.
Diet can be helpful as well. One study shows that low fat diet, with increased protein intake was effective at raising RMR. The same study notes that the best results are achieved by combining the diet with strength training.