Metabolism

Metabolism refers to all the chemical reactions by which the body converts nutrients into energy, building materials, and waste products. It is a fundamental requirement for life - without a functioning metabolism, the body couldn't maintain temperature, repair cells, or produce energy for movement and thinking. Metabolism is divided into two main types: anabolism (building reactions, such as muscle protein synthesis and bone renewal) and catabolism (breakdown reactions, such as fat burning and glycogen breakdown for energy). These processes occur simultaneously in every cell of the body, around the clock.

Basal metabolic rate or BMR (Basal Metabolic Rate) accounts for 60-70% of total daily energy expenditure. It includes everything the body does automatically: breathing, blood circulation, nervous system function, hormone production, cell renewal, and temperature regulation. Typically, a woman's basal metabolic rate is approximately 1300-1500 kcal and a man's 1600-1900 kcal per day. The remaining energy expenditure consists of the thermic effect of food (TEF, approximately 10%) and physical activity (20-30%).

Factors affecting metabolism are numerous. The single most important factor is muscle mass: each kilogram of muscle burns approximately 13 kcal per day at rest, while a kilogram of fat burns only about 4.5 kcal. Age slows metabolism by approximately 2-3% per decade after age 30, but this is mainly due to loss of muscle mass - not aging itself. Sex plays a role in that men have on average more muscle mass and therefore a faster metabolism. Hormones - especially thyroid hormones (T3 and T4) - directly regulate the speed of metabolism. Genetics, stress levels, sleep quality, and even ambient temperature also have an effect.

Speeding up metabolism is one of the most searched topics in the context of weight management. Research has shown the most effective methods to be: 1) Resistance training - strength training permanently increases metabolically active tissue. Just 2-3 workouts per week is sufficient. 2) Adequate protein intake - protein's thermic effect is 20-30%, meaning the body uses about a quarter of protein's energy just for digestion, compared to 5-10% for carbohydrates and only 0-3% for fats. 3) Sufficient sleep (7-9 hours) - sleep deprivation disrupts hormonal balance and lowers metabolism. 4) Increasing daily activity (NEAT) - walking, taking stairs, and general movement can increase expenditure by up to 500 kcal per day. 5) Cold exposure - in cold conditions, the body activates brown fat tissue for heat production, which increases energy expenditure.

One of the most common myths is 'slow metabolism' as the cause of being overweight. Studies show that differences in basal metabolic rate between people of the same size and age are typically only 200-300 kcal per day - not thousands of calories, as is often believed. Paradoxically, overweight individuals generally have a *faster* metabolism than normal-weight people, because a larger body requires more energy for maintenance. True 'slow metabolism' is usually related to hypothyroidism, which is worth checking with a doctor through blood tests if weight loss isn't progressing at all despite a normal calorie deficit.

Another significant myth is that certain foods or supplements 'boost' metabolism significantly. Green tea, chili, and coffee can temporarily raise metabolism by 3-8%, but in practice this means only 30-80 extra calories per day - not a decisive difference in weight management.

Metabolic adaptation is the metabolism's natural adjustment mechanism. When you eat too little for too long - especially under 1200 kcal per day - the body enters energy-saving mode: basal metabolic rate drops by up to 20-30%, body temperature decreases, daily activity unconsciously decreases, and hormone production is disrupted. This explains why strict diets work at first but slow down, and after stopping, weight returns easily. Metabolic adaptation can be avoided with a moderate calorie deficit size (300-500 kcal below TDEE) and regular maintenance phases.

Practical tips for supporting metabolism: never eat below your resting calories long-term, do strength training 2-4 times per week, eat sufficient protein (1.6-2.2 g/kg/day), sleep 7-9 hours, stay active in daily life, and avoid extreme diets. Metabolism is directly connected to BMR, TDEE, resting calories, and calorie deficit concepts.

Last updated: March 30, 2026