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Visorių g. 2, Vilnius
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Metabolism is the biological basis that determines how the body extracts energy from food, how muscles grow, and how weight is maintained. However, many myths surround this concept: some blame "slow metabolism" for weight gain, while others hope for miraculous supplements that would speed it up in a few days.
The reality is much more specific. The metabolic rate is shaped by measurable factors: genetics, muscle mass, hormones, and daily habits, and their effects are based on precise scientific logic, not advertising phrases.
It is further explained how metabolism works at the cellular level, what symptoms indicate its disorders, the differences between "fast" and "slow" types, and scientifically proven ways to sustainably speed it up.
Metabolism encompasses all chemical reactions in the body that convert food into energy and building materials for cells. These reactions occur continuously in every cell and ensure basic vital functions, growth, and renewal.
The process is divided into two directions. Catabolism breaks down complex molecules (carbohydrates, fats, proteins) into simpler ones, releasing energy in the form of ATP. Anabolism, on the other hand, uses energy to create more complex structures, such as muscle protein synthesis after exercise or the formation of new cells.
Total daily energy expenditure consists of four components:
BMR makes up the largest portion because even during sleep, the body needs energy for heartbeat, breathing, brain activity, maintaining body temperature, and hormone production. These functions operate 24 hours a day, so their energy demand exceeds even the expenditure of intense training.
Metabolism is often confused with digestion, but digestion is only one part of the bigger picture. The TEF component, responsible for food processing, accounts for just 5–15% of daily energy expenditure. The remaining metabolic activity includes all biochemical processes at the cellular level, from oxygen transport to fatty acid oxidation in the mitochondria.
The speed of metabolism is shaped by several interrelated factors: genetics, muscle mass, age, sex, hormones, body composition, and physical activity. Each of these contributes to how much energy the body uses per day.
Muscle mass is one of the most important indicators. A muscular person burns more calories at rest because muscle tissue is metabolically more active than fat and requires a constant energy supply to maintain cellular functions.
Sex also affects BMR. Men generally have a higher basal metabolism due to greater muscle mass and a lower percentage of fat compared to women.
The influence of age is often overestimated. A 2021 study by Pontzer and colleagues, published in the journal "Science," showed that metabolism remains stable from about 20 to 60 years of age. Significant slowing, about 0.7% per year, begins only after 60. Weight gain in middle age is more often associated with reduced activity and muscle loss, not metabolism itself.
Hormones complete this picture. Thyroid hormones T3 and T4 directly regulate how quickly cells produce energy, so imbalances in their levels can significantly change the metabolic rate.
The difference between "fast" and "slow" metabolism is often much smaller than assumed. In reality, the BMR difference between people of similar size, age, and sex is only up to 200–300 kcal per day, not thousands as popular myths claim.
The greatest individual difference is determined by NEAT (non-exercise activity thermogenesis): unconscious daily movement: walking, gesturing, restless sitting, or changing posture. According to energy expenditure studies, the NEAT difference between two people can reach up to 1000 kcal per day.
Therefore, people with a "fast metabolism" are usually not genetic exceptions. They simply eat less naturally due to a lower appetite and move more without noticing. That is why thin people often say "I eat everything," although in reality their energy balance remains stable.
However, an excessively "fast" metabolism can also be a signal. Sudden weight loss, increased heart rate, excessive sweating, and irritability often indicate hyperthyroidism, an overactive thyroid. In such cases, a TSH test and an endocrinologist consultation are necessary.
The myth about "overloading metabolism" by eating more also does not hold up to criticism. The body temporarily increases TEF, but this does not cause a long-term magical acceleration. On the contrary, with a constant calorie surplus, energy expenditure increases only due to increased body weight, not because of faster metabolism.
Slowed metabolism manifests with several characteristic signs that develop gradually and last longer than a few weeks. The most commonly observed symptoms are:
These signs are often associated with hypothyroidism, when the thyroid produces too little T3 and T4 hormones, causing metabolism to slow down. If symptoms are persistent, an endocrinologist usually prescribes a TSH test, which shows thyroid function.
However, it is necessary to distinguish a true medical condition from the popular "slow metabolism" myth. For most people complaining of slowed metabolism, the real cause is reduced daily movement or insufficient nutrition, not the BMR itself.
Moreover, long-term strict diets cause adaptive thermogenesis: the body reduces energy expenditure adapting to calorie deficit, so weight stops dropping despite restricted eating.
It is worth consulting a doctor when symptoms last longer than a few weeks and are combined with pulse changes, significant hair loss, or unexplained weight changes. Self-diagnosis based on one symptom is unreliable.
Metabolism can be influenced through four areas: nutrition, physical activity, sleep, and hydration. These factors work together, so a single change yields limited results. Sustainable effect is achieved when all areas are combined daily, not applied episodically.
Proteins have the greatest impact on metabolism through the thermic effect of food (TEF): their digestion consumes about 20–30% of the calories obtained, while carbohydrates account for 5–10%, and fats only 0–3%. Therefore, a protein-rich diet makes the body work more intensively even at rest.
Metabolism-supporting products include eggs, cottage cheese, legumes, chili pepper (due to capsaicin), broccoli, flax seeds, and green tea. These products combine proteins, fibers, and bioactive compounds that together support energy expenditure.
Hydration is no less important. Even mild dehydration can reduce basal metabolism by a few percent, so 1.5–2 liters of water per day is a minimal guideline for an active person.
For athletes, reaching the daily norm of 1.6–2.2 g of protein per kilogram of body weight from food alone can be challenging, so quality protein supplements are helpful to compensate for daily deficits after training or on busy days.
In fat metabolism, an important role is played by L-carnitine, a compound resembling an amino acid that transports fatty acids into mitochondria where they are converted into energy.
Strength training is the most effective way to increase long-term BMR, as each additional kilogram of muscle burns about 13 kcal per day at rest. Over a year, this becomes a significant difference that cardio training alone cannot achieve.
Interval HIIT training works through another mechanism: the EPOC effect (increased oxygen consumption after training). The body burns extra calories during recovery, and this effect can last up to 24 hours after intense exercise.
However, the greatest hidden contribution often comes from NEAT, daily unconscious movement. Taking stairs instead of the elevator, walking during breaks, standing work, and even gesturing can add 200–500 kcal per day, exceeding the expenditure of most workouts.
The best result comes from a combination: 2–3 strength training sessions per week to build muscle mass, 1–2 cardio sessions for cardiovascular health, and consistently active daily life. These three pillars complement each other and work through different physiological mechanisms.
You can find broader context in the article about weight loss, where physical activity is combined with dietary changes.
Sleep directly regulates hormones that control appetite and energy expenditure. When sleeping less than 6 hours, cortisol and ghrelin levels increase, while leptin decreases. The body signals hunger even when energy is sufficient, and daily movement naturally decreases.
Chronic stress acts similarly. Constantly elevated cortisol promotes abdominal fat accumulation and can disrupt thyroid function, leading to decreased T3 hormone activity and slowed metabolism.
For sustainable results, 7–9 hours of sleep, a regular sleep schedule, and daily stress management practices are recommended: breathing exercises, walking outdoors, or meditation.
Energy utilization is also influenced by insulin sensitivity, which depends on carbohydrate choice. Complex carbohydrates with fiber maintain a more stable glucose level, so the body uses the obtained energy more efficiently instead of storing it as fat.
Metabolism is the sum of all chemical reactions in the body that convert food into energy and building materials for cells. These reactions occur continuously, even when a person is resting or sleeping.
The process consists of two parts. Catabolism breaks down nutrients to release energy, while anabolism uses it to build new cells, muscles, and tissues.
The simplest comparison is the body's engine running 24/7. It never turns off because even during sleep the heart beats, lungs work, and cells renew.
A fast metabolism is neither an advantage nor a disadvantage by itself, and the concept is often misunderstood. The BMR difference between people of similar size, age, and sex is only up to 300 kcal per day, so talk about radically different metabolism is usually a myth.
The real explanation for individual differences is NEAT, unconscious daily movement, which can differ by up to 1000 kcal per day between two people.
However, excessively rapid weight loss, heavy sweating, and increased heart rate may indicate thyroid hyperactivity (hyperthyroidism). In such cases, it is necessary to consult a doctor and perform a TSH test.
The most common signs of slowed metabolism are constant fatigue, unexplained weight gain, feeling cold even in a warm environment, dry skin and hair loss, and digestive problems, especially constipation.
When these symptoms last longer than a few weeks and occur together, they may indicate hypothyroidism. It is worth consulting an endocrinologist and performing a TSH test to assess thyroid function.
However, in most cases, there is no real metabolic disease. The problem is usually decreased daily activity, insufficient sleep, or long-term calorie deficit, not the metabolism itself.
No, metabolism slows down with age much less than commonly thought. A 2021 study by Pontzer and colleagues, published in the journal "Science", showed that basal metabolic rate remains stable from age 20 to about 60, and significant slowing (about 0.7% per year) begins only after 60.
Thus, weight gain in middle age is usually related not to metabolism itself, but to decreasing muscle mass, reduced daily activity, and hormonal changes. These factors can be corrected with strength training, protein intake, and regular movement.
A balanced diet and regular physical activity are the most reliable ways to maintain a healthy metabolism, but appropriate supplements can help achieve results faster. Quality proteins help maintain muscle mass, which directly affects basal metabolism since muscles burn more calories even at rest.
In the Papildupasaulis.lt assortment, you will find everything you need for your goal, from sports proteins to fat burners and other products that help active people. Visit the store at Visorių g. 2, Vilnius, or order online and get products delivered straight to your home.
