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What kind of stuff are we made of?

The old saying goes that “little girls were made of sugar and spice and everything nice and little boys were made of snakes and snails and puppy-dog tails.” That definition might have sufficed when we were young, but as adults we know that what we are made of is a lot more complex. Furthermore, changing what we are made through weight loss and improved fitness all too often proves very challenging.


When we step on a scale, it registers the total weight or mass of our body. However, this is just a general measurement and does not really provide us with an accurate assessment of the individual contributions made by the different types of substances to our weight. Said another way, the scale is not sensitive to body composition.


If we break the himan body all the way down to its most simplified form we would discover that the elements carbon, hydrogen, oxygen, and nitrogen make up greater than 90 percent of our body weight. We also acknowledged that these elements are components of the major types of molecules in our body in the form of water, protein, fat (triglycerides) and carbohydrates. Meanwhile, minerals make up most of our remaining body weight.

Energy Metabolism, Body Weight & Composition ...

What Is The Composition Of Our Body?

  • What kind of stuff are we made of?
  • How do the different tissues contribute to our weight?
  • Why do we store excessive energy as fat?

If we were able to remove the water from our body, we would find that we are then mostly made up of energy molecules such as protein, fat, and carbohydrate. In fact, greater than 80 percent of what would be left over is energy providing substances in one form or another. So we can be viewed as a container of energy similar to the foods we eat. This is important for when we are not satisfying our energy needs with external sources (food), we are able to power bodily functions by tearing down internal energy sources. Keep in mind that our cells are tireless in their operational efforts and must be fed twenty-four hours a day.


How do the different tissues contribute to our weight?

While it is interesting to know how much water, protein, fat, carbohydrate and minerals are found in the body it is often more helpful to take it up a level and look at the contributing tissue. In fact, the contribution of various tissues explains the relative contributions made by the different molecules and minerals.


Muscle and fat (adipose tissue) are typically the greatest contributors to body weight. For instance, a generally lean, fit man will be about 40-45% muscle and 14-17% body fat. That means that muscle and fat make up half to about two-thirds of his body mass. For this man, bone might contribute about 8% and the skin 2%. The rest of body weight is comprised of organs and tissue such as the heart, lungs, liver, kidneys, intestines, pancreas, brain, spinal cord and our circulations (blood, lympahatic).

Why do we store excessive energy as fat?

We store most of the excessive energy we consume in the form of body fat. It is a matter of efficiency as more than double the amount of energy can be stored in a gram of fat than in carbohydrate and protein (9 calories vs 4 calories per gram). Furthermore, carbohydrate and protein attract water, thus storing excessive energy exclusively as glycogen or protein would increase body water tremendously. For instance, each gram of glycogen attracts about 3 grams of water. Thus storing energy primarily as carbohydrate or protein would make us much heavier, larger, and somewhat waterlogged. This would be a huge disadvantage, as body weight would likely to at least double if possible at all!

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