Total Body Mass vs Body Weight

TBM vs Body Weight

First let’s do some Maths literacy and look at defining ‘mass, weight and matter’.

Mass is the quantity of matter of an object.

Matter is anything that takes up space by having volume.

Weight is how heavy something is, so the amount of force that acts on the mass.

The human body is made up of matter therefore it has mass therefore the gravity of this mass is measured with weight.

Whoa! Now that you know the difference let’s look at what the composition of the human body is actually is.

When we measure body weight, what are we really measuring?
The total mass of the human body is made up of many different life giving tissues:

  • The skeletal system comprising of bones, ligaments, tendons and other connective tissue which is about 20% of total body weight.
  • The muscular system is approximately 40% of a person’s total body weight. You have more than 600 muscles by the way! Included in this is not just the skeletal muscle but the heart muscle, digestive organs and blood vessels.
  • Total body water is approximately 65% of the human body with about ⅔ inside the cell walls (intracellular) and ⅓ outside the cells (extracellular).
  • Our blood volume is between 7 and 10% of our body weight. Blood volume increases as body weight increases.
  • Fat mass – we have essential fat mass which is important for regulating body temperature and is also a form of energy storage. It also cushions organs and is very important for reproductive functions and bone health. We also have non essential fat mass which is excess fatty acids that are stored around the organs as visceral fat and under the skin as subcutaneous fat.

Why does my weight fluctuate?
Day to day it is normal for weight to fluctuate and it can be up to a couple of kilograms. That seems a lot but the body is in a constant growth, repair and maintenance cycle. Fluctuations can be due to hormones, whether you’ve had a bowel movement, excess sodium and fluid retention or your hydration status. Long term weight cycling (fluctuation) which is seen as a result of ‘yo yo dieting’ can lead to a poor health status. There’s a higher risk of metabolic disorders like cardiovascular disease.

What really matters then – weight or body composition?
The health and composition of your body’s tissues are more important than weight alone. Unfortunately, many people have goals of weight loss without understanding of the importance of body composition. It is true that undertaking exercise alongside a healthy diet can help build muscle, strength and fitness and result in fat loss. If that improves your health status, that’s great but if an exercise regime is undertaken along with a diet low in an adequate supply of energy by not eating enough; this can result in more detrimental health outcomes. Short term looking to long term dietary and exercise patterns along with adequate sleep and reduced stress matter more in improving your health status than the number on the scale.


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