Do you own a fitness watch that not only measures your steps and heart rate, but also tells you how many calories you have allegedly burned? Do not believe the alleged calorie expenditure that your fitness watch displays. This calculation can deviate by up to 92% from your actual expenditure. It is impossible to accurately calculate your individual calorie needs based solely on certain parameters such as height, weight and activity level. This number can only provide a rough guideline, as your calorie expenditure is highly individual and depends on many factors that fitness watches are unable to even take into account. It comprises your basal metabolic rate, your physical activity level, the thermic effect of food and food-induced thermogenesis. To find out exactly what these terms mean and how they affect your calorie expenditure, keep on reading.
Basal metabolic rate
The basal metabolic rate is the amount of energy your body needs at complete rest under thermoneutral conditions (27-31°C for undressed people and 20-22°C for dressed people). The basal metabolic rate keeps the body's vital processes running. This includes involuntary mechanical processes, such as sustaining the cardiovascular system, breathing or maintaining muscle tone. It also includes supplying the organs with nutrient- and oxygen-rich blood, as well as cellular growth, remodeling and maintenance processes. The basal metabolic rate depends on your age, your sex, your height, your body composition, your hormones, possible illnesses, possibly being on medication, stress and the climate which you live in. Each of these influencing factors is individual and determines your basal metabolic rate.
For example, with increasing age, the metabolic processes in the body continuously slow down and with the reduction in muscle mass which often coincides with the ageing process, the basal metabolic rate also decreases. Taller people have a larger body surface area, which releases more heat into the environment, as well as a higher mass of body tissue. All of this requires additional energy. The ratio of muscle to fat tissue also plays an important role: muscle tissue consumes 3-5 times more energy than fat tissue (depending on the study). An underactive thyroid, for example, can also have a negative impact on your basal metabolic rate.
Physical activity level
The physical activity level is the amount of energy that the body needs in 24 hours beyond the basal metabolic rate. This includes, for example, physical and mental activity, work, exercise, thermoregulation in different climates, or regeneration and recovery after illness or injury. This can be your commute to work, your daily routine at work (i.e. whether you have a job that requires manual labor or not), going for a walk or exercising. It is important to note that involuntary movements, such as moving your feet, gesticulating or playing around with objects, are also an important factor and can have a major impact on your calorie expenditure. A person who moves a lot (voluntarily or involuntarily) will have a higher metabolic rate than a person who has an inactive lifestyle and mostly sits or lies still.
The basal metabolic rate and the physical activity level are relatively well-known factors when conversing about calorie expenditure. However, this is also influenced by the thermic effect of food and food-induced thermogenesis, which are less well known.
Thermic effect of food
The thermic effect of food is the amount of energy lost through digestion. Since not all nutrients are fully digested and absorbed in the gut, a digestive loss of up to 10% can be expected. In addition, the metabolic processes during digestion further increase the energy expenditure after eating. The various macronutrients require different amounts of energy for digestion, metabolization and transport processes in the body. The digestion of fats has the lowest metabolic rate with an increase of 2-4% of the basal metabolic rate. For carbohydrates it is 7% and for proteins even 18-24%. The effect is greatest with proteins because the process of breaking them down takes up to 18 hours, meaning that more energy is required to support the metabolic processes than with carbohydrates and fats.
Food induced thermogenesis
Food-induced thermogenesis refers to the increase in energy expenditure following food intake, which increases the body temperature and leads to a transmission of heat. This also requires around 10% of the energy consumed. Such heat loss can also be triggered by smoking, caffeine or constant restlessness, for example.
Conclusion
In other words, no fitness watch in the world is able to take all these factors into consideration and therefore definitively determine your individual energy expenditure. Fitness watches are super inaccurate when it comes to specifying calorie expenditure, as they are unable to factor in many of the aspects that determine our “real” calorie expenditure. And how should that be possible? Our calorie expenditure is super unique and it is very likely that two people of the same weight, height and age will still have varying calorie expenditures. No fitness watch in the world can take into account, for example, your involuntary movements, your stress level, your hormone level, your exact body composition, the medication you are on or the climate you are in. They will also never be able to factor in food-induced thermogenesis or the thermic effect of food. So please do not get carried away by the calorie expenditure displayed on your fitness watch and ideally do not even look at it. Instead, focus on your diet and see where you can improve it. I'd be happy to help you with that!
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