Metabolism Explained – Learn How a Body’s Metabolism Works


Metabolism is ultimately a collection of chemical reactions that takes place in the body’s cells converting the fuel in the food we eat into the energy needed to power everything we do, from moving to thinking to growing. In fact, thousands of metabolic reactions happen at the same time – all regulated by the body – to keep our cells healthy and working.

There are two processes, or rather, two interactive channels by which metabolism runs.

  • Catabolism refers to the breakdown of food components (such as carbohydrates, proteins and fats) into their simpler forms, which can then be used to create energy. Think of it as your “destructive metabolism” which produces the energy required for all activity in the cells. In this process, cells break down carbohydrates and fats to release energy and fuel all anabolic reactions, such as heating the body, giving the muscles power to contract and the body to move. As complex chemical units are broken down into more simple substances, the waste products released in the process of catabolism are removed from the body through the skin, kidneys, lungs, and intestines.
  • Anabolism is your “constructive metabolism” that gives which is all about building and storing. All anabolic processes support the growth of new cells, the maintenance of body tissues, and the storage of energy for use in the future.

These are governed by your Hormonal and Nervous systems. Interestingly, they work together like a team complimenting every single cellular action in your body.

Trying to determine your caloric need for the day? Your body’s metabolic rate (or total energy expenditure) is the one that says it all – you are what you eat, how you move, how much you rest and how well all cells and tissues are able to recuperate. Energy expenditure is continuous, but the rate varies throughout the day. The lowest rate of energy expenditure is usually in the early morning.

The complexity of metabolism can be divided into three components:

  1. Basal metabolic rate (BMR) – is the amount of kilojoules burned at rest and contributes 50-80% of your energy used. The BMR refers to the amount of energy your body needs to maintain itself. This accounts for 50-80% of your total energy use. Total lean mass, especially muscle mass, is largely responsible for the BMR. So, anything that reduces lean mass will reduce BMR. That’s why it’s important to preserve muscle mass when you try to lose weight, since the BMR accounts for so much of the energy we use. An average male may have a BMR of around 7,100kJ per day, while an average female may have a BMR of around 5,900kJ per day.
  2. Energy used during physical activity – this is the amount of kilojoules burned during movement and physical activity. The energy expenditure of the muscles makes up only 20% or so of the total energy expenditure at rest but, during strenuous exercise, the rate of energy expenditure of the muscles may go up 50-fold or more. Since energy used during exercise is the only form of energy expenditure that you have any control over, take advantage of this phenomenon and start moving more!
  3. Thermic effect of food – this is the energy you use to eat, digest and metabolize food. Regardless of what you thought before, eating actually raises your metabolism. No wonder diet-obsessed meal-skippers burn fewer calories AND have no energy to move. After each meal, the metabolic rise occurs soon after you start eating and peaks two to three hours later. It can range between 2-3% and up to 25-30%, depending on the size of the meal and the types of foods eaten. Fats raise the BMR by 4%, carbohydrates by 6% and proteins by up to 30%! Hot spicy foods can also have a significant thermic effect.

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About Author

Elena Voropay

Elena Voropay is a Certified Personal Trainer, Fitness Instructor and Certified Nutritionist. She also holds accreditations for her knowledge in Iridology and Herbal Medicine. Elena has conducted presentations and lectured on various health, fitness and science-related topics. See my profile page for more information!

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