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What do we mean when we say ‘metabolism’

By Darren O'Toole | In Health | on August 22, 2019

In the fitness industry, the word ‘metabolism’ is banded about frivolously – mainly in order to justify getting a client to do something that they don’t want to. Burpees: ‘It’ll get your metabolism up’, Heavy squats: ‘it’s good for the metabolism’ etc.

So, when we talk about ‘metabolism’, what are we talking about? Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the human body as a whole. Essentially these falls into two main categories: the breakdown of molecules to obtain usable energy; and the production of molecules that are needed by the cells.

Resting metabolic rate

Food is the fundamental building block in developing a higher metabolic rate. Exercise and having lean muscle tissue does play a role, however it is our ingestion of food which will be pivotal. Eat too little and our metabolism slows right down. This concept is a real pain when we discuss weight loss. This is because our resting metabolic rate (RMR) – the rate at which your body burns energy when it is at complete rest – will slow when we are in a period of dieting.
Also losing weight means your subsequent RMR is lower – doesn’t seem fair, right? Plus to top it all off, as we age our RMR drops further too.

Calculate your resting metabolic rate

For the maths buffs amongst you, if you wished to work out, roughly, what your RMR is, the calculations are below.

Harris-Benedict Equation for BMR

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)

Darren’s example
BMR = 88.362 + (13.397 x 70) + (4.799 x 172) – (5.677 x 33) =
BMR = 88.362 + (937.79) + (825.43) – (187.34) = 1664 kcals

From my example, this calculation says that for all of my bodily functions to take place, without any notable form of movement, I would burn 1664kcals each day.

The type of bodily functions that we are discussing here include:
• Body heat production
• Bone formation
• Muscle development
• Brain functioning
• Digestion and excretion
• Breathing and blood circulation
• Detoxification of the liver and kidneys
• Fat storage
• Protein formation

This is why some personal trainers will say that a workout will cause a rise in your metabolism. If you consider that the energy required to perform all of these activities on a 24/7 basis. Now add to that a workout which will increase your body’s heat, it’ll require an excess production of proteins and muscular development; they’ll impact on levels of fat storage plus an undoubted rise in circulation and breathing rate. The training stimulus will lead to a greater calorie burn that goes beyond the session itself ie, a rise in your metabolism.

Do we need to eat this much?

However a note of caution. My first being that I feel these calculations allow for excess caloric intake. To suggest that most women burn 1400kcals and men 1600kcals without moving a finger seems a dubious claim. My feelings are that, observing the rising levels of obesity, our RMR may be lower than these predictions and calculations suggest.

Secondly, these calculations could be hugely more accurate if they took into consideration 1. Lean muscle tissue; and 2. The levels of weight loss that have occurred on a week-to-week basis. These factors would highly determine a difference in two people of identical weight, height and age.

Fighting your body

Weight loss and changes to body composition will never be an exact science. In fact, the more we read, the harder it can be to decipher what is true for mass populations. However, what remains a constant, is that our bodies have a fundamental role to keep us as near to homeostasis as possible. In other words, our body aims to not change too much. It seeks to help us to maintain our weight. This means that it can be hard to pack on muscle and when we do, our body will find it easier to lose it than it was for us to build it. It also means that it is hard for us to lose body fat once we have established it. Neither seem quite fair! But the primary message is this: you’ll not get the body you wish without dedication and sacrifice. You’re going to be fighting against your body to get the body you want. Understand that, and you’ll have a greater understanding of what you need to do.

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