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Metabolism, energy and nutrient requirement

Published: October 28, 2016


Metabolism: your body's clockwork
Metabolism: your body's clockwork
According to certain headlines you can boost your metabolism in 5 easy steps, lose weight by improving your metabolism, and rev up your metabolism by eating certain foods and performing specific types of exercise.
If you have an interest in losing weight, or maintaining a healthy body weight and being physically active you have probably come across the word "metabolism".
But, what do we mean by "metabolism" and what is the relationship between the nutrients we consume and metabolism?
What is metabolism?

  • the sum total of all the chemical reactions that occur in living cells to maintain life
  • chemical or metabolic reactions are involved in the synthesis and degradation of organic molecules, and the extraction, storage and use of energy from organic compounds within the cells of living organisms
  • every metabolic or chemical reaction requires energy
  • energy metabolism refers to all of the chemical reactions by which energy is obtained from food and expended by the millions of cells in your body in some way
  • digestion one metabolic pathway wherein the carbohydrate, fat and protein contained in the food that you eat is broken into glucose, fatty acids, amino acids, and vitamins and minerals which can be absorbed into your body
  • three other cellular metabolic pathways break down glucose, fatty acids and amino acids to release energy in the form of ATP the energy molecule
  • vitamins, minerals, and other nutrients contained in the food you eat, as well as water are required for these metabolic pathways to function optimally

The food and beverages you consume are the fundamental source of nutrients which supply your body with energy and the essential components which your body requires for metabolic reactions.  Some of these nutrients such as glucose and fatty acids can be stored in your body.  Amino acids are not stored in your body in significant amounts.

What is the relationship between metabolism and energy requirement?
Your metabolism is closely tied to your energy requirement and the number of calories you need to consume. However, human metabolism is highly complex and there are many factors which affect your metabolism.

  • Basal metabolic rate (BMR): the rate at which your body uses energy when at complete digestive, physical and emotional rest under specified conditions.
  • Resting metabolic rate (RMR): similar to BMR, but the testing criteria are less stringent and the measurement is usually higher than that for BMR.
  • Metabolic activity differs according to cell type and function: brain, liver, heart and kidneys account for 60% of BMR. Muscle mass accounts for approximately 25% of BMR while bones, glands, small and large intestines and skin account for 15-20% of metabolic activity. Body fat accounts for approximately 5% of metabolic activity. 

Major factors which affect BMR include:

  • age: BMR decreases with age generally due to loss of lean tissue
  • life stage: growth years, pregnancy, and breast feeding increase BMR
  • gender: men in general have a higher BMR than women usually due to increased muscle mass
  • height: taller people have higher BMR than shorter people
  • body weight: higher body weight increases BMR

Body leanness, fever, illness, stress, some drugs, caffeine, nicotine, environmental temperature, starvation, fasting, malnutrition, weight loss, hormones and sleep also influence your BMR in some way. Link to the full article to learn more.

Energy is also required for:

  • Physical activity generally increases BMR
  • Thermic effect of food: different nutrients require different amounts of energy for digestion and absorption
  • Thermoregulation: maintenance of your body’s core temperature influences your BMR

What is the relationship between metabolism, energy and nutrient requirement?

Whether you are focused on weight loss, weight maintenance, weight gain, and/or physical activity and exercise performance understanding how nutrients interact in metabolism can help you achieve your goals.
You cannot change many of the factors which influence your BMR.
However, consuming a varied diet containing adequate carbohydrate, fat, protein, and vitamins and minerals, and ensuring that you have adequate physical activity in your daily routine you may be able to optimise your metabolism and your energy requirement.
Human metabolism is a complex process. Weight maintenance is often presented as energy in = energy out, but this is an over simplification.
Weight gain is not only about eating more and/or expending less energy and weight loss is not merely about eating less and/or expending more energy.
You need to take into account the all factors that affect your BMR most of which you cannot change.
Link to the full article to learn how weight gain and loss affects your BMR and energy requirement

Related Topics

Digestion  Metabolism  Your Body 


Whitney, E. & Rady Rolfes, S. (2005). Understanding Nutrition. Belmont, CA: Thomson Wadsworth
Gropper, S.S., Smith, J.L. & Groff, J.L. (2005). Advanced Nutrition and Human Metabolism (4thEd.). Belmont, CA: Thomson Wadsworth.
Horton et al. (2002). Principles of Biochemistry (3rd Ed.). Upper Saddle River, NJ. Prentice Hall