What does Metabolism actually mean?

Sometimes I feel there is terminology that we use in terms of Nutrition, Health, Wellness, Fitness without really understanding what it is. We’ve heard the words through media or possibly studied it in school but do we really understand what it means? And more importantly how to make it relevant to how we live. So that is why I have chosen to write this post today about Metabolism.

Starting at the beginning, what is your metabolism? Despite what many think, metabolism is not just an organ or a muscle that we can adapt and control. Michael Jensen obesity researcher from the Mayo Clinic describes metabolism as a “series of chemical processes in each cell that turn the calories you eat in to fuel to keep you alive” 1. What’s important to note is that it is a series of processes in the body that need to work together to work efficiently? And what is relevant to understand if you have a kink in the chain the resulting reactions might not be favourable for you.

If you are anything like I am, when I first starting looking at nutrition all those years ago, my brain shut down when I heard things like BMR, RMR. I just wanted to know what to eat. However this is not how it works, because you need to know your body so that you can make the better choices.

We consume food to fuel ourselves.

Our body needs energy for 3 main reasons…

  1. Basal Metabolic Rate is the energy we need when you are actively doing nothing but your body is silently working away. It’s the calories you use as you function: the energy your heart, liver, kidneys, muscles, brain and even your fat store needs. And super interestingly for most people this series of interaction uses about 70% of the energy we consume.
  2. Digestion requires energy, so breaking down what you eat into a form that your body can use to create energy to fuel your daily actions EVEN requires energy. This is a thing we call the thermic effect of food and it uses 10% of the energy we consume.
  3. Physical Activity is usually accepted to use about 20% of our energy intake. That is unless you are working out for multiple hours or have a very physical active job. This is a key point to note in terms of influencing weight. Physical activity has more impact metabolism than BMR and Digestion, this we have very little control over.

Something that is important for you to know is that science does not yet understand why one person can eat more than another person and not put on weight, we don’t completely understand that mechanism YET. I know this might be hugely frustrating and you might not want to hear this. However I offer you this piece of knowledge so that you do not get sucked in by the next headline that claims to “BOOST your Metabolism and loose all your body FAT in 3 weeks”. This is particularly relevant during these uncertain times where we are all feeling a tad vulnerable about our health.

We do know there are determinants of how fast your metabolism might be, some of the kinks in the chain.

  1. Genetics – a very curious question for many researchers.
  2. Sex – women might notice a higher metabolic rate in the first half of their cycle(3).
  3. Muscle/Fat ratio – muscle burns more calories than fat, you know this one. But does that mean you can eat what you want? Unfortunately not, one still needs to thin about how much they need to fuel BMR, Digestion and the activity(4).
  4. Age – naturally you just slow down and still very much so a mystery.
  5. Stress & emotions – acute stress might make you want to eat less while chronic stress might lead to poorer food choice, body weight gain, hormonal disruptions and energy use (5).

We have learned that major restriction or dieting can slow down your metabolism.

The short term gain is that you lose the weight and feel better, yay! However I have some news for you, many current studies are now showing that those who lose that weight rapidly ultimately end up regaining the weight after a period of time. Why is this? Well if you’ve been at a particular weight for a period of time, the body gets happy there. Our body and brain are lazy, they like being comfortable. And for reasons not fully understood yet, our body does everything it can to get back to this metallic set point, the one where it’s comfortable (6).




Right so we’ve had the basics of what it is, what might impact it and it might be all sounding a little gloomy.
But hold that feeling, its not all bad. I am no scientist but it seems to me that if we can get our body comfortable at this new set point we have the possibility of influencing weight even with a slower metabolism. Many clients I work with are undernourished, what do I mean? Basically they aren’t eating enough to fuel this BMR and digestion energy need of our body. So if we focus on fuelling our body with adequate but balanced nutrition and increasing movement, could we gradually shift your muscle/body fat ratio to your favour without sending that series of chemical processes in a whirlwind of chaos?

“Without self-acceptance, self-improvement is only noise.” Anon
I feel is really important for all goals, but in terms of my discussion here today, its so relevant for weight loss goals and understanding metabolism.




Just as you do not want to accept this slower metabolism, I did not want to accept I have a gene that triggers my skin condition. However the longer I kept fighting the inevitable the more stressed I became and the more inflamed the evidence of this struggle was. After much support, I choose to acknowledge my feelings around my condition and over the longer term with many lifestyle changes, the inflammation reduced, the inner battle subsided. Over time I grew to not only accept but to appreciate what my body was telling me.

The thing about lifestyle changes is that it just doesn’t happen that one day you get up and live this new way forever more. As we all know about the last diet we followed, one day a point comes where something so unsettling pulls us back to our old behaviours. Do you know why? Because that’s where we feel comfortable, both our body and our mind. We learn and live through rewards, when you eat cake, you feel good and whatever discomfort you were feeling will most likely soften. This is the cool habit loop that we survive in, we like to feel good.

And when you think of the CRASH diet, I haven’t heard too many people say they get much of that positive feeling from the bag of lettuce. Because diets guide you towards a reward that is only received if the weighing scales tells you the numbers you want to see. A lifestyle change happens when you being to feel the reward in the moment, when you being to understand those triggers for behaviour and interact with them in a new way.

And I don’t want to let you off this week without anything to practice. Something that might be interesting for you to think about is to have a check of what your BMR is, you can do it here. Have a think of how much you do actually eat? Do you give yourself enough calories? Are you exercising more but eating less? Are you searching for a number in the hope that it will bring happiness? Or could you accept things as they are, practice eating with pleasure and slowly see the changes unfold in your life while FEELING happier today in the skin you are in.

Have a restful Sunday,



  1. Belluz, J. (2020). Your metabolism starts slowing down at age 18, and other facts about a widely misunderstood process. Retrieved 3 October 2020, from https://www.vox.com/2016/5/18/11685254/metabolism-definition-booster-weight-loss
  2. Lazzer, S., O’Malley, G., & Vermorel, M. (2020). Metabolic And Mechanical Cost Of Sedentary And Physical Activities In Obese Children And Adolescents [Ebook]. ECOG.
  3. Comitato, R., Saba, A., Turrini, A., Arganini, C., & Virgili, F. (2014). Sex Hormones and Macronutrient Metabolism. Critical Reviews In Food Science And Nutrition, 55(2), 227-241. doi: 10.1080/10408398.2011.651177
  4. Park, J., & Kim, S. (2016). Validity of muscle-to-fat ratio as a predictor of adult metabolic syndrome. Journal Of Physical Therapy Science, 28(3), 1036-1045. doi: 10.1589/jpts.28.1036
  5. Van der Kooij, M. (2020). The impact of chronic stress on energy metabolism. Molecular And Cellular Neuroscience, 107, 103525. doi: 10.1016/j.mcn.2020.103525
  6. Aamodt, S. (2020). Retrieved from https://www.ted.com/talks/sandra_aamodt_why_dieting_doesn_t_usually_work?language=en

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