What is Metabolism?

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Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the organism. Metabolism can be conveniently divided into two categories:

  • Catabolism - the breakdown of molecules to obtain energy
  • Anabolism - the synthesis of all compounds needed by the cells

Metabolism is closely linked to nutrition and the availability of nutrients. Bioenergetics is a term that describes the biochemical or metabolic pathways by which the cell ultimately obtains energy. Energy formation is one of the vital components of metabolism.

metabolismImage Credit: VectorMine / Shutterstock.com

Nutrition, metabolism and energy

Nutrition is the key to metabolism. The pathways of metabolism rely upon nutrients that they breakdown in order to produce energy. This energy in turn is required by the body to synthesize molecules like new proteins and nucleic acids (DNA, RNA).

Nutrients in relation to metabolism encompass factors like bodily requirements for various substances, individual functions in the body, the amount needed, and the level below which poor health results.

Essential nutrients supply energy (calories) and supply the necessary chemicals which the body itself cannot synthesize. Food provides a variety of substances that are essential for the building, upkeep, and repair of body tissues, and for the efficient functioning of the body.

The diet needs essential nutrients like carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, and around 20 other inorganic elements. The major elements are supplied in carbohydrates, lipids, and protein. In addition, vitamins, minerals and water are necessary.

Carbohydrates in metabolism

Foods supply carbohydrates in three forms: starch, sugar, and cellulose (fiber). Starches and sugars form major and essential sources of energy for humans. Fibers contribute to bulk in diet.

Body tissues depend on glucose for all activities. Carbohydrates and sugars yield glucose by digestion or metabolism.

The overall reaction for the combustion of glucose is written as:

C6H12O6 + 6 O2 -----> 6 CO2 + 6 H2O + energy

Most people consume around half of their diet as carbohydrates. This comes from foods such as rice, wheat, bread, potatoes and pasta.

Proteins in metabolism

Proteins are the main tissue builders in the body. They are part of every cell in the body. Proteins help in cell structure, functions, hemoglobin formation to carry oxygen, enzymes to carry out vital reactions and a myriad of other functions in the body. Proteins are also vital in supplying nitrogen for DNA and RNA genetic material and energy production.

Proteins are necessary for nutrition because they contain amino acids. Among the 20 or more amino acids, the human body is unable to synthesize 8 and these are called essential amino acids.

The essential amino acids include:

  • Lysine
  • Tryptophan
  • Methionine
  • Leucine
  • Isoleucine
  • Phenylalanine
  • Valine
  • Threonine

Foods with the best quality protein are eggs, milk, soybeans, meats, vegetables, and grains.

Fat in metabolism

Fats are concentrated sources of energy. They produce twice as much energy as either carbohydrates or protein on a weight basis.

The functions of fats include:

  • Helping to form the cellular structure;
  • Forming a protective cushion and insulation around vital organs;
  • Helping absorb fat-soluble vitamins,
  • Providing a reserve storage for energy

Essential fatty acids include unsaturated fatty acids like linoleic, linolenic, and arachidonic acids. These need to be taken in diet. Saturated fats, along with cholesterol, have been implicated in arteriosclerosis and heart disease.

Minerals and vitamins in metabolism

The minerals in foods do not contribute directly to energy needs but are important as body regulators and play a role in metabolic pathways of the body. More than 50 elements are found in the human body. About 25 elements have been found to be essential, meaning a deficiency produces specific deficiency symptoms.

Important minerals include:

  • Calcium
  • Phosphorus
  • Iron
  • Sodium
  • Potassium
  • Chloride ions
  • Copper
  • Cobalt
  • Manganese
  • Zinc
  • Magnesium
  • Fluorine
  • Iodine

Vitamins are essential organic compounds that the human body cannot synthesize by itself and must, therefore, be present in the diet. Vitamins particularly important in metabolism include:

  • Vitamin A
  • B2 (riboflavin)
  • Niacin or nicotinic acid
  • Pantothenic Acid

vitamins and mineralsImage Credit: Siberian Art / Shutterstock.com

Metabolic pathways

The chemical reactions of metabolism are organized into metabolic pathways. These allow the basic chemicals from nutrition to be transformed through a series of steps into another chemical, by a sequence of enzymes.

Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy. These reactions also are coupled with those that release energy. As enzymes act as catalysts they allow these reactions to proceed quickly and efficiently. Enzymes also allow the regulation of metabolic pathways in response to changes in the cell's environment or signals from other cells.


Further Reading

Last Updated: Jun 14, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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  1. mohammad yasin mohammad yasin United States says:

    Lenir Richardson.. Try to put yourself on vegetable no bread nor rice, just vegetable for three months and do exercise too. You`ll see the different.

    You can blend your vegetable and fruit together in a blender if you wish to do so too. I am working in the medical field and this method works perfect.

  2. Mutethya Makau Mutethya Makau Kenya says:

    This is good work. however, it needs to be revised. For instance the paragraph ('The diet needs essential nutrients like carbon, hydrogen, oxygen...') is not very clear because what you have given there are elements but not nutrients.

  3. Roxy Powers Roxy Powers United States says:

    What nutrients are NOT broken down into smaller pieces during by metabolism?

  4. Omprakash Pawar Omprakash Pawar India says:

    Very very good knowledge gained. I was on the way to boycott potatoes. But from reading this material it shows that potatoes is essential as it contains carbohydrate which in turn is helpful to build metabolism

  5. Agnes Neal Agnes Neal United States says:

    Is it true that it is hard to keep warm if metabolism is low?

  6. Michele Cinowski Michele Cinowski United States says:

    What is my problem, suddenly I have lost all my fat and in five months lost over 50pounds. Been through tests but no one can find a answer.I weigh 92 pounds and feel very sick all the time. What to do next?

  7. Gillian Woolleson Gillian Woolleson United Kingdom says:

    Michelle re your sudden weight loss, have you had any tests done, blood, thyroid etc? I lost a lot of weight rather quickly and I went to my doctor about it I had blood tests done and I was diagnosed diabetic plus I have thyroid issues as well, the symptoms you described are the same, diabetes attacks the fat first and then attacks the muscles in fact diabetes affects all the organs in the body, so get yourself tested asap you are seriously under weight good luck

  8. Mathieu Bishara Mathieu Bishara Canada says:

    It would be very helpful if o got a response

  9. carl james jimenez carl james jimenez Philippines says:

    My metabolism is not deactivated to fatten me how to do the solution?

  10. BBalta BB BBalta BB Colombia says:

    i have this homework and it asks me how does the metabolism of a skinny person works? what makes a person not gain weight? and imaginary, what would happend and how would happen if a fat person with bad metabolism changes radically its metabolism? sorry for my english

  11. Guruprasad Panamalai Guruprasad Panamalai India says:

    If metabolism in a person's body system fails, does it affect the kidney function?

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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