Metabolism | What we need to know

27.11.2025

Metabolism is the process of converting food consumed by the body into energy, which is necessary for the life of the organism and the proper functioning of vital functions such as breathing, digestion, blood circulation, contraction of the heart muscle, etc.

Table of Contents

Metabolism is a set of biochemical processes that occur continuously in each cell.

When we think about metabolism, we often focus on how the body burns calories from food and drink. This is known as metabolic rate and includes:

Energy used for basic (basal) functions, such as breathing, heart rate, etc.
The energy needed to digest and process food

The energy that the body needs for physical activity

Metabolism is a complex system that is not easy to change.

What is the function of metabolism?

As mentioned, metabolism is a continuous process that ensures the production of energy from food to ensure all vital functions, such as:

Breathing
Blood circulation
Digestion of food
Growth and cell renewal
Hormone production
Maintaining body temperature

All of these processes require the cell to work continuously, both during activity and at rest, and to adapt to a changing environment. The need for adaptive processes arises:

Hunger
Physical activity
Illness and injuries
During pregnancy and lactation
etc

This means that the “rate” of metabolism is not always at the same level. At different times, metabolic processes require different amounts of energy production and expenditure.

Metabolic processes

Metabolism generally consists of two main processes - anabolism and catabolism.

Catabolism The process of breaking down macronutrients, during which energy is generated and released. The energy generated during catabolism is used by the entire organism – from cellular processes to motor movements.

Through catabolic reactions:

Polysaccharides, or complex carbohydrates, are broken down into simple carbohydrates – sugars. Starch is broken down into glucose, which enters the blood and, with the help of insulin, reaches the cells. Glucose absorbed by the body is stored in the muscles and liver in the form of a more complex carbohydrate – glycogen. Carbohydrates obtained with food and glycogen accumulated in the body – are one of the most important sources of energy for the production of vital functions.
Proteins are broken down into amino acids, which are used in the body to make other proteins. When needed, the products of protein breakdown are used to synthesize glucose.

The energy released during the breakdown of nutrients is stored in cells (mainly in muscles) in the form of adenosine triphosphate (ATP) molecules.

Anabolism The opposite process of catabolism is the process of synthesis, from simple units, to produce more complex structures. Anabolic processes involve the synthesis of new proteins, the formation of cells, and the renewal of tissues. Bone tissue renewal, muscle mass growth, and mineralization are examples of anabolism.

A number of anabolic hormones are involved in the process of anabolism:

Growth hormone: A hormone produced by the pituitary gland that stimulates the process of growth and renewal.
Insulin: A hormone produced by the beta cells of the pancreas that converts glucose from food into a form that cells can absorb.
Testosterone: The hormone responsible for the development of male characteristics, which stimulates the growth of bone and muscle mass.
Estrogen: A hormone responsible for the development of female sexual characteristics, which is also involved in the process of bone mineralization.

How does metabolism affect weight?

The regulation of the metabolic process is determined by the body's needs. Metabolism is not the isolated cause of weight gain or loss, although various processes in the body determine how many calories are spent on a particular process.

Body weight is defined as the difference between the energy produced by the body during catabolism and the energy expended during anabolism. Excess energy is stored as fat (in adipose tissue) or as glycogen (in the liver and muscles).

1 gram of fat produces 9 calories, while 1 gram of protein and 4 gram of carbohydrates only produce 4 calories.

Although obesity and adiposity are usually the result of excess calories being consumed and stored as fat, sometimes hormonal and other disorders prevent the body from fully utilizing energy, contributing to the development of obesity.

What is the difference between fast and slow metabolism?

A fast basal metabolism implies a high calorie expenditure for basal functions, while a slow metabolism requires fewer calories to perform these functions. However, metabolism is a very complex and multi-component process, so its empirical connection with body mass is incorrect.

There are several methods for calculating the calorie intake required by the body, which take into account:

Body size and build type: The more muscle mass you have in relation to fat mass, the more calories your body needs.
Age: As we age, our body's calorie needs decrease. The main reason for this is a decrease in muscle mass.
Hormones: The lower the level of anabolic hormones, the fewer calories the body needs. As we age, testosterone production decreases in men and estrogen production in women. Both hormones are important anabolic hormones.
Physical activity: Older people are less physically active, which also reduces their body's need for energy.
Gender: Men have a faster metabolism than women. This is due to their greater muscle mass, so men need much more calories than women.

What does metabolic disorders mean?

A metabolic disorder refers to any condition in which the body's use of energy is disrupted. The symptoms of metabolic disorders are related to which process(es) in the body are disrupted.

The main causes of metabolic disorders are:

Nutrient deficiencies. For example, vitamin D deficiency causes a deficiency in the body's ability to absorb and utilize calcium. Iron deficiency causes anemia, etc.
Calorie deficit or excess. Insufficient calorie intake over a long period of time reduces basal metabolic rate. Prolonged consumption of excess calories leads to fat storage and weight gain.
Enzyme deficiency. Enzyme deficiency is mainly hereditary/genetic in nature. For example, phenylketonuria - the accumulation of phenylalanine due to a deficiency of the enzymes that break it down, which leads to degeneration of the child's nervous system and developmental delays.
Hormonal imbalance. An imbalance of thyroid hormones, which manifests as hypothyroidism, often causes a slow metabolism, which is accompanied by weight gain, lack of energy, hair loss, and more.
Side effects of medications, some toxins, and substances. Long-term use of some medications, such as steroids, can cause weight gain, swelling, and insulin resistance. Long-term use of alcohol or other toxic substances disrupts the metabolic processes of the liver.

Acquired metabolic disorders

Most acquired metabolic disorders primarily involve the endocrine system and manifest as hormonal imbalances. The development of acquired metabolic syndromes is mainly caused by pathologies of organs involved in metabolism or autoimmune processes:

Diabetes mellitus
Diseases of the thyroid gland
Weight loss or obesity
Metabolic syndrome
Insulin resistance
Cushing's syndrome (adrenal gland damage)

Inborn metabolic disorders

Also known as inborn errors of metabolism. This group of dysmetabolisms includes conditions in which the process of processing and assimilation of a particular nutrient is disrupted due to a genetic deficiency of a specific enzyme or biologically active substance. There are many genetic metabolic disorders. Some of them are very rare:

Glycogen storage disease
Hemochromatosis
Lysosomal storage diseases
Prickly pear syrup syndrome
Mitochondrial diseases
Tay-Sachs disease
Wilson's disease and others

How to maintain a healthy metabolism?

The health of metabolic processes is usually less dependent on the individual. However, there are specific steps we can take to help maintain a healthy metabolism and overall health:

Healthy diet. It is essential that the body's basic functions are constantly supplied with energy. Therefore, regular meals are important. Long gaps between meals or a prolonged calorie deficit slow down metabolic processes, which affects not only body weight, but also cell renewal processes and general health.
The right food products And choosing the right amounts. Monocomponent diets usually have a negative impact on our physical and mental health. Therefore, food must necessarily contain a properly balanced amount of protein, fat, and carbohydrates.
physical activity It is important for maintaining muscle mass. Muscle mass burns the most calories. The less muscle you have, the slower your metabolism.
sleep – Sufficient duration and quality. Chronic sleep deprivation disrupts cell renewal, the proper functioning of the immune system, and contributes to hormonal imbalance, which ultimately leads to a slowdown in metabolism, weight gain, swelling, and a number of other processes.
Fluid intake – Since all processes in cells involve water molecules, water deficiency has a critical impact on metabolic processes.
From extreme diets or prolonged starvation Restraint. Critically reducing calorie intake slows down many metabolic processes.

How to control metabolism?

Metabolic status can be monitored through regular laboratory tests. The following groups of tests are mainly used to assess metabolic status:

Liver function tests
Kidney function tests
electrolytes
Thyroid hormones
Reproductive system hormones
Vitamins
lipid spectrum
Glucose and insulin study
proteins and amino acids
Enzymes
etc

It is recommended to perform metabolic panel tests at least once a year. In the presence of risk factors or chronic diseases, additional instrumental and laboratory tests may be necessary.