Metabolism: The Complete Guide

If you run a fitness facility, metabolism is a word you hear every day. Trainers on your floor promise sessions that will speed it up, fitness magazines build entire issues around it, and members arrive with firm opinions about what does and does not work. If the idea is that popular, there must be something behind it. But what exactly? And what is metabolism in the first place?

Most people, asked to define it in a sentence, end up repeating the word itself. That is not much use to an operator who has to choose equipment, build a timetable and answer members honestly. So this guide takes the subject as a whole, in plain language, and then translates it into what it actually means for a professional gym floor.

What is metabolism?

Metabolism is the set of chemical processes that take place in every cell of the body and convert the calories you consume into the energy you need to function. It supplies energy for every activity of life, including ones as simple as breathing, sleeping or reading.

Fundamentally, metabolism covers two opposite processes: catabolism and anabolism.

Catabolism is the breakdown of large particles, such as proteins or fats, into smaller ones, such as amino acids and fatty acids. When you digest a meal, catabolism breaks each food down into smaller units so that it can supply energy, for example in the form of glucose.

Anabolism is the opposite process. It is responsible for combining small molecules, such as amino acids, into larger structures. Its main job is growth and construction. Bone development and muscle gain are anabolic processes, and so is wound healing: layers of new tissue form around the wound as a result of anabolism.

Why does this matter to you? Because it explains one principle that underpins every training programme you will ever host. If a member wants to build or maintain muscle mass, the body has to be put into an anabolic state, which is achieved among other things through strength training. If the goal is to shed fat tissue, the body has to spend more time in a catabolic state, which cardio training helps to drive. That is the physiological reason a serious facility needs both a strength area and a cardio area, not one or the other.

Metabolism and the functions of daily life

The body is a remarkably complex piece of machinery. Every minute of your life, whatever you happen to be doing, thousands of chemical reactions are running inside it to keep your cells and organs healthy and working.

To keep operating at its best, the body needs a supply of energy, and that supply comes from the food and drink consumed during the day. It spends that energy in several distinct ways.

• Resting energy. This is the absolutely fundamental amount of energy the body needs to function correctly when you are doing nothing at all: beating the heart, distributing blood to the cells and maintaining an adequate body temperature. At this level, metabolism is called resting metabolism, and it usually accounts for 60 to 80 percent of total energy needs. For an average healthy man, the accepted energy figure is 7 100 kJ, or 1 700 calories per day. For an average healthy woman, it is 5 900 kJ, or 1 400 calories per day. It is worth remembering that the body’s energy expenditure changes over the course of the day and decreases with age, which means that the older you are, the fewer calories your body burns at rest.
• The energy needed to digest food. This is known as the thermic effect: the energy required to digest, absorb and eliminate food. It is estimated to use around 10 percent of your total daily energy.
• The energy spent on physical activity. This is by far the most variable component, generally representing 20 to 50 percent of the body’s total expenditure. It is not only sport that feeds into it, but also everyday and recreational movement: standing, walking, dancing, even cooking.
• The energy spent while sleeping. This is the part of metabolism that keeps working while you sleep. According to many experts, it runs at greater intensity in the second half of the night, when the body is in deep sleep.

These components are estimates and their ranges overlap, so they should be read as orders of magnitude rather than as a budget that adds up neatly to one hundred percent. The practical conclusion is stable regardless: the only line an operator can genuinely influence is the activity line.

Factors that affect metabolism

Many factors influence the rate of your metabolism, among them eating habits, activity level, genetics, sex, age and body composition. Some of them deserve a closer look.

• Emotional state. It will hardly come as a revelation that stress is not good for your metabolism, but there is evidence behind the claim. Research shows that stress reduces the number of calories burned after a high-fat meal. Scientists also link metabolism to another mental health condition, depression. The explanation runs as follows: if your metabolism is working properly, your energy level should stay stable and high during the day, which stops you feeling tired, and when you do not feel tired your mood is generally better too.
• Sleep. Sleep matters for more than its restorative properties. It also maintains the hormonal and metabolic processes of the body. Insufficient sleep or sleep disorders can disrupt those processes and lead to increased oxidative stress, glucose intolerance and insulin resistance.
• Nutrition. What you eat has a significant impact on how your metabolism functions, because the nutrients you supply are the raw material from which the hormones regulating metabolic rate are built. A balanced diet based on good-quality products and rich in nutrients supports normal metabolic function. Without it, metabolic disturbances can develop over time into more serious conditions.
• Activity level. The positive effect of physical exercise on metabolic rate has been known for a long time, and recent research only confirms it. One study looked closely at 200 metabolites, the substances produced during metabolic processes, which show how metabolism responds to activity. The results showed that systematic physical exercise not only consumes a very large amount of energy, but that a large share of it comes from fat. That in turn affects the efficient use of protein in the body, the building of lean muscle mass and the loss of fat tissue.
• Age. Most people become less and less physically active as they get older, and metabolism slows accordingly. Research suggests, however, that metabolism does not respond to age so much as to activity level. So if you want to look after your metabolism, do not neglect daily exercise, whatever your age.

The components of daily energy expenditure at a glance

How to look after a healthy metabolism

The headline advice is simple: stay active, sleep well, eat sensibly and avoid excessive stress. That is general enough to be useless on its own, so here is what it looks like in practice.

• Activity. Try to find even a short moment every day for physical exercise. It can be a session at home, a visit to the gym, running, cycling or swimming. Whatever the format, make time for it, and if you genuinely cannot find any, use one of the short workouts designed for the busiest people.
• Sleep. Be regular. Aim not only for a certain number of hours, but for falling asleep and waking up at the same times.
• Nutrition. Follow a balanced diet, based on as many unprocessed products as possible, providing good sources of carbohydrates, protein and fat as well as vitamins and minerals. Eat frequently, at least five times a day, and remember to drink water regularly.
• Stress. Stress in itself is useful and helps you handle future situations better, but excessive stress is a threat. If you have problems at work, at school or in a relationship, look for solutions rather than despairing. If you feel overwhelmed, make sure you find time and a way to relax, whether that is seeing a psychologist, listening to music, visiting a spa or meeting friends. You will never eliminate stress completely, and you do not need to.

What this means for a professional facility

For an operator, the practical lesson is that the activity line is the only one your equipment can move, and that it moves in two different directions depending on what you install. Strength equipment supports the anabolic side, cardio equipment drives the catabolic side, and a floor that offers only one of the two will always disappoint half of your members.

It also explains why an accessible, low-barrier entry point matters as much as the heaviest machine in the room. Since metabolism responds to activity level rather than to age, the members who benefit most from your facility are often the ones least likely to walk in unaided: older members, deconditioned beginners and people returning after a long break. Equipment they can use without supervision, and a floor plan that does not intimidate them, is what turns a physiological argument into actual attendance.

You can build both sides from our ranges of professional cardio equipment and professional strength training machines.

Frequently asked questions

Can you really speed up your metabolism with training?

You can influence total energy expenditure, mainly through the activity component, which is the most variable of them all. Resting metabolism can also be affected indirectly, since building lean muscle mass changes body composition. What no single session does is transform metabolic rate overnight.

Does metabolism inevitably slow with age?

Expenditure at rest does decrease with age, but the research cited above suggests that metabolism responds far more to activity level than to age itself. Most of the slowdown people attribute to getting older tracks the fact that they move less.

Is cardio or strength training better for metabolism?

They do different jobs. Cardio training drives the catabolic side and is the more direct route to reducing fat tissue; strength training drives the anabolic side and builds the lean muscle mass that supports resting expenditure. A facility that programmes both serves its members better than one that picks a side.

Why does sleep appear in a metabolism guide?

Because sleep maintains the hormonal and metabolic processes of the body. Poor or insufficient sleep is associated with oxidative stress, glucose intolerance and insulin resistance, which is why it belongs in the same conversation as diet and training.

Turning the theory into a floor plan

Understanding metabolism is useful precisely because it stops equipment choices being arbitrary. Anabolism and catabolism are not marketing words: they describe the two things your members come to you for, and they map directly onto the two halves of a well-specified gym.