SCIENCEY TIME
Our resting metabolic rate (RMR) is simply the amount of energy that we burn whilst we are doing nothing, and generally makes up 60-75% of our daily energy use.
Essentially this represents the energy that is needed to maintain all of the body’s normal functions like breathing, pumping blood, thinking, producing hormones, and millions of other processes which our body just gets on with, without us being any the wiser. Of course, however fast or slow our RMR is will impact our waistline, with some slim people claiming a ‘fast metabolism’ being the reason for their success, and others using ‘slow metabolism’ as an excuse for their failures.
So, what factors actually influence RMR, and can we do anything to change it?
Fat-Free Mass
Thought to account for up to 85% of the variance in RMR Main contributors to energy use at rest are kidneys (7%), heart (10%), skeletal muscle (18%), brain (19%), liver (27%), and other sources (i.e. bones, lungs, intestines) (19%) Quite simply, larger bodies take more energy to run!
Whilst we cannot change the size of our organs, we can alter how much muscle mass we have, with each 1 kg added thought to increase RMR by around 50 kcal
Age
Our RMR is thought to decline by around 2% for each decade that we age The main change is that we tend to carry less muscle mass as we get older, due to reduced hormone production and being less likely to exercise strenuously
Gender
Women have an RMR which is generally 5-10% lower than men Again, the main factor is that women tend to have more fat and less muscle mass than men (whilst I’m sure that many of us wishes this were not the case, it’s simply a matter of biology)
Fat is not a metabolically active tissue, so it does not use energy, but muscle is; so, more muscle = more energy burning
Others
The menstrual cycle can impact RMR, showing 5-10% increases during the luteal phase There are some suggested differences between ethnicities, with Caucasians showing around 5% higher RMR than African American counterparts Body temperature can also have a large impact, with ranges of 33-38ᵒC being considered normal – an increase of temperature by 1ᵒC is thought to increase RMR by 13% The number of hormones our body produces can also have an impact; however, claiming low thyroid functions is far more popular than the medical prevalence which is less than 2% of people.
So, there are a number of factors which will impact how quickly we burn energy. Unless we are some strange creature that can alter our body size, age, or ethnicity, then the only factor from the above list which we can alter is how much muscle mass we have. This is why I think that any good weight-loss intervention should incorporate some form of muscle building strategy; meaning resistance exercise and a diet filled with high quality protein. Basically, gain more muscle > burn more energy > make it easier to achieve a calorie deficit
As a final side note, avoid any pharmaceuticals or supplements which claim to speed up metabolism as at best you will be wasting money, and at worst you could be doing yourself harm.
Leave a Reply