Can you burn calories when doing absolutely nothing?

What is your ‘metabolism’? 

There are lots of misleading claims suggesting ways in which you can manipulate your metabolism; such as eating certain foods, drinking green tea, or “try this diet to boost your metabolism and lose weight.” However, the evidence to support these claims is pretty much non-existent for this somewhat mysterious biological process. Your metabolism is not a muscle that you can flex and control; it’s in every cell of your body. Metabolism is a chemical process that turns the calories you eat into fuel. When we refer to ‘basal metabolic rate’ (BMR), or ‘resting metabolic rate’ (RMR), we are talking about the calories you burn when you are doing nothing. Your vital organs such as the brain, liver, heart and kidneys etc, account for about half of the energy burned at rest, while the digestive system, fat and muscles account for the rest.

So where does exercise come into this?

The benefits of physical activity on your metabolism when resting has been shown to have a direct effect on the total amount of energy used throughout the day, compared to the total amount of energy you would use just to complete the activity. As RMR accounts for most of our energy expenditure, an increase in the overall expenditure in response to physical activity, will make a significant difference to your total daily expenditure (energy used).Studies have shown that regular exercise increases lean muscle mass which subsequently raises RMR. This is because muscle mass burns more calories purely for just existing alone. Interestingly though, extreme exercise can potentially reduce RMR due to the body going in to ‘flight mode’. The body can interpret extreme levels and duration of exercise as ‘flight’ and so reduces RMR to preserve energy when at rest in preparation for another ‘flight episode’. 

What’s the happy medium?

To improve RMR through physical activity, the level of intensity needs to be considered. Exercise that places the body in training related distress may induce fatigue and provoke metabolic, hormonal and neural responses, which will slow the RMR to restore and conserve energy. By keeping the intensity of exercise low, the body will not enter into a state of exercise induced distress and will therefore help raise RMR by increasing lean muscle mass and promote fat burning. Whilst the science behind all of this is very fascinating, the most important thing to remember is the enjoyment factor! If exercise is something of a chore, we are less likely to engage in it at all! 

References:

Maunder, E. Plews, DJ. and Kilding, AE. (2018) Contextualising Maximal Fat Oxidation During Exercise: Determinants and Normative Values. Front Physiol.9 : 59 9. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5974542 (Accessed 24/09/2020). 
 

Speakman, J. and Selman, C. (2013) Physical activity and resting metabolic rate. Available at: https://www.ncbi.nlm.nih.gov/pubmed/14692598 (Accessed 24/09/2020). 
 

Woods, AL. Rice, AJ. And Garvican-Lewis ,LA. (2018) The effects of intensified training on resting metabolic rate (RMR), body composition and performance in trained cyclists.Available at: https://www.ncbi.nlm.nih.gov/pubmed/29444097 (Accessed 24/09/2020).