Definition of Metabolism
Metabolism is a term used to describe all the chemical reactions that occur in our body to sustain life. It includes processes such as digestion, absorption, transport, and utilization of nutrients from food. Our metabolism also involves the synthesis of new molecules and the breakdown of old ones.
Metabolism can be divided into two primary categories: anabolism and catabolism. Anabolism refers to the building up of complex molecules from simpler ones, such as the synthesis of proteins from amino acids. Catabolism, on the other hand, refers to the breakdown of complex molecules into simpler ones, such as the breakdown of glucose into energy.
Functions of Metabolism
Metabolism performs several essential functions within our body, some of which include:
- Energy Production: The primary function of metabolism is to convert food into energy that can be used by the body to perform various activities such as walking, running, and more.
- Growth and Repair: Metabolism is also responsible for the growth and repair of body tissues. It helps to replace damaged or dead cells with new ones.
- Waste Elimination: Metabolism eliminates waste products from the body by breaking them down and excreting them through urine and feces.
- Hormone Regulation: Metabolism helps regulate the production and secretion of hormones within the body, which are responsible for various bodily functions.
Measurement unit
Kilocalorie (which is equal to 1000 calories) is the unit we typically use to measure metabolism, and describes the amount of energy that the body expends while performing various activities. This is because the energy we obtain from food is also usually measured in kilocalories. One kilocalorie is the amount of energy required to raise the temperature of 1kg of water by one degree Celsius. In the next section, we will explore the components of our total daily energy expenditure, or in other words, the calories we burn in a day.
Total Daily Energy Expenditure
TDEE stands for Total Daily Energy Expenditure, which refers to the amount of energy, or calories, that a person burns in a day through various activities such as resting, moving, and exercising. It includes the Basal Metabolic Rate (BMR), Non-Exercise Activity Thermogenesis (NEAT), Thermic Effect of Food (TEF), and Exercise Activity Thermogenesis (EAT).
- BMR is the amount of energy the body requires to maintain basic life functions such as breathing, circulating blood, and maintaining body temperature while at rest. It accounts for around 60-75% of the total daily energy expenditure. BMR is influenced by factors such as age, gender, body mass and composition, and hormonal levels. It’s important to note that the genetic component accounts for only 3-8% of variation in the basic metabolic rate.
- TEF is the energy required for digestion, absorption, and metabolism of food. It accounts for approximately 7-15% of the total daily energy expenditure.
- NEAT refers to the energy expended for all activities of daily living that are not intentional exercise or sports-related. It includes activities such as walking, standing, and doing household chores. NEAT can vary significantly between individuals depending on their level of daily movement and habits.
- EAT is the energy expended during intentional exercise or physical activity. It can include activities such as running, cycling, weight lifting, and sports. EAT can vary significantly between individuals depending on their level of physical activity.
How to Improve Your Metabolism in Practice
Understanding Total Daily Energy Expenditure (TDEE) is empowering because it shows that metabolism isn’t something fixed or broken, it’s largely shaped by daily behaviors. While you can’t directly “control” your metabolism, you can influence the components that make it up in practical, sustainable ways.
Let’s break down what that looks like in everyday life.
1. Supporting Your BMR: Build and Preserve Muscle
Since Basal Metabolic Rate (BMR) accounts for the largest portion of your daily energy expenditure, the most effective way to support it is by maintaining or increasing lean muscle mass.
In practice, this means:
- Including strength training 2–4 times per week (bodyweight, resistance bands, or weights all count)
- Eating enough protein throughout the day to support muscle repair and maintenance
- Avoiding extreme calorie restriction, which can lead to muscle loss and a lower resting energy expenditure over time
2. Increase NEAT: Move More Without “Exercising”
NEAT (Non-Exercise Activity Thermogenesis) is one of the most overlooked—but powerful—ways to increase daily energy expenditure. Small movements throughout the day can add up significantly.
In practice, this looks like:
- Walking while taking phone calls
- Taking the stairs instead of the elevator
- Standing up or stretching every 30–60 minutes
- Doing household tasks like cleaning, cooking, or gardening
- Parking farther away or getting off public transport one stop earlier
3. Use Exercise Strategically (EAT)
Exercise Activity Thermogenesis (EAT) plays a smaller role in total calorie burn than many people expect, but it’s still essential for metabolic health, muscle preservation, and long-term sustainability.
In practice:
- Combine strength training with moderate cardio
- Choose activities you enjoy (walking, cycling, swimming, classes, sports)
- Focus on building a routine you can maintain long term, not burning the most calories in one session
4. Optimize the Thermic Effect of Food (TEF)
TEF is the energy your body uses to digest and process food. While it’s a smaller contributor to TDEE, your food choices still matter.
In practice:
- Prioritize protein-rich foods, which have a higher thermic effect than fats or carbohydrates
- Eat regular meals instead of skipping meals and overeating later
- Choose whole, minimally processed foods that require more digestion
As you can see, your metabolism has more to do with your actions than some magical curse that people can’t dispel. All the talk about “slow metabolism” is pure marketing to scare individuals into buying some non scientifical and useless solution, you can read more about it here.
Conclusions
Having analyzed and explained the phenomenon, we can consequently derive a set of deductions. Many people believe that they have a slow metabolism, which makes it difficult for them to lose weight. Pathological subjects aside (see thyroid dysfunction), there are no subjects with “slow” or “fast” metabolisms, but there are more or less sedentary individuals, with more or less dense body compositions and more or less thermogenic diets. The main factor that will influence metabolism will therefore be lifestyle.
A healthy diet, with a good share of proteins, will increase TEF. An active lifestyle will contribute to high levels of NEAT. Physical exercise will contribute even more to daily energy expenditure and to the improvement of body composition by increasing BMR and EAT.
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