Metabolism : What is it?


A person’s metabolism describes the sum of all the chemical reactions that are occurring in the body at any one time.  These (bio)chemical reactions include those that break down food into energy which is needed to move our muscles, as well as reactions involved in body maintenance, growth, and repair.

Every moment of our lives we have many chemical reactions occurring that release energy from the fat, carbohydrate, and protein either from the food that we eat or our body’s energy stores.  At the same time there are many reactions occurring that use this energy from food just to keep us alive as an organisation of many trillions of individual cells.  This transfer of energy between energy producing (or catabolic) reactions and energy consuming (or anabolic) reaction is not 100 percent efficient and some of the energy involved in each reaction is lost as heat.  Indeed, this is where our body heat comes from.

Except for relatively small amounts of energy used for doing mechanical work, or that stored in the body when we grow, all metabolism results in heat.  So, if we were to put ourselves in a room which could measure the body’s heat production (and we sat still and were not growing) the heat produced by our bodies would represent the net rate of all the chemical reactions going on at that time.  This is what we call our metabolic rate and direct measurement of heat release from the body to measure our metabolism is called ‘calorimetry’.

Calorimeters that can fit in a person are large, expensive and rare.  Only specialist scientific institutions or universities would have these.  Fortunately there is another way of measuring metabolic rate.  ‘Indirect calorimetry’ is based on the fact that the heat produced from our bodies is directly proportional to the amount of oxygen our bodies consume.  Thus, the rate at which we consume oxygen is proportional to the rate at which our body produces heat.  Consequently, our metabolic rate is often simply expressed as the rate at which we use oxygen (denoted as VO2) in litres per minute (L/min).  The maximum rate at which we consume oxygen (thus, our maximal sustainable metabolic rate) is termed our VO2max.  It is well know that success in many sporting events requires a person to have a high VO2max.

More about VO2max in upcoming articles.

The only way to fuel metabolism is via the energy in the food we eat.  If we eat food energy at a greater rate than our metabolic rate requires we stores the excess energy on our body, primarily as fat.  If we don’t eat enough food energy to support our metabolism, then we use up some of the body’s energy stores – hopefully fat!  Considering more than half of NZ adults are overweight or obese (i.e. we have stored too much energy on their bodies as fat), most of us are interested in ways to increase our metabolic rate so that the latter scenario will apply.  We will investigate various ways in which we can increase our metabolism in the next article.

For the next article in this series:
Metabolism part 2 – Hit the Turbo Click here….

Dr Stephen Stannard is a senior lecturer at Massey University with expertise in metabolism and exercise; he also has professional interests in prolonged exercise, the effects of fasting and type II diabetes.

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The views expressed in this article are not necessarily those shared by Body Concepts Ltd. Content is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always consult a doctor before undertaking an exercise or nutritional plan.

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