# How Caloric Deficit and Basal Metabolism Work ## Basal Metabolism (BMR) **Basal Metabolic Rate (
Weight loss is one of those topics that seems to come up on every street corner. Yet the more information that becomes available, the greater the confusion seems to be. Diets promising miracles in two weeks are replaced by trendy nutritional movements, social media is full of contradictory advice, and people get lost in it all. And yet the foundation of successful and, above all, sustainable weight loss is surprisingly simple – it rests on two pillars that are closely connected: understanding basal metabolic rate and correctly setting a caloric deficit. Once a person truly understands these two concepts and learns to work with them, they stop looking for shortcuts and start building results that last.
Imagine Petra, a thirty-four-year-old accountant from Brno, who decided to lose about ten kilograms after her second pregnancy. She tried intermittent fasting, a gluten-free diet, and popular detox programmes. She always shed a few kilograms, but they came back after a few months. It was only when she started to look into how much energy her body actually needed and how to set a sensible deficit that she began achieving results that this time stuck. Her story is not an exception – it is the experience of thousands of people who stopped experimenting and started approaching weight loss systematically.
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What is basal metabolic rate and why is it so important
Basal metabolic rate, abbreviated BMR, represents the amount of energy the body consumes at complete rest – solely to maintain basic vital functions. It is the energy needed for breathing, maintaining body temperature, and the functioning of the heart, kidneys, brain, and other organs. In other words, even if a person were to lie still all day without sleeping, their body would still burn a certain number of calories. And this number is surprisingly high – in the average adult woman it ranges from around 1,300 to 1,600 kilocalories per day, and in men between 1,600 and 2,000 kilocalories.
Basal metabolic rate accounts for 60 to 75% of most people's total daily energy expenditure. This means that movement, sport, and everyday activities make up only the remaining portion. This is precisely why knowing this number is so important – if someone sets their caloric intake below their basal metabolic rate, they are literally depriving their body of the energy needed to survive. The result is not faster weight loss, but rather a slowing of the metabolism, loss of muscle mass, fatigue, and hormonal imbalance.
A whole range of factors influence basal metabolic rate. Age plays a crucial role – as the years pass, metabolism naturally slows down, by approximately 2% per decade after the age of thirty. Sex significantly affects BMR, because men generally have more muscle mass, which is metabolically more active than fat. Height and overall body weight are also important, but particularly body composition – two people with the same weight can have markedly different basal metabolic rates depending on their ratio of muscle to fat. Genetics, thyroid function, and hormonal balance further complicate this equation.
How can basal metabolic rate be calculated? Several formulas are available, and the most widely used and at the same time most accurate for the general population is the Harris-Benedict equation, which was last revised in 1984 by scientists Mifflin and St Jeor. The so-called Mifflin-St Jeor formula is as follows:
- For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
- For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
A specific example: a thirty-five-year-old woman weighing 70 kilograms and measuring 165 centimetres has a basal metabolic rate of approximately 1,469 kilocalories. However, this number still does not represent total daily energy expenditure – it is merely the foundation from which further calculations are made.
Caloric deficit: how to set it correctly for sustainable weight loss
Once a person knows their basal metabolic rate, it needs to be converted into total daily energy expenditure, which also accounts for physical activity. For this purpose, the so-called PAL coefficient (Physical Activity Level) is used, by which BMR is multiplied. A sedentary lifestyle without exercise corresponds to a value of 1.2, light activity one to three times a week adds a coefficient of 1.375, moderate activity three to five times a week corresponds to 1.55, and very active people or athletes work with values of 1.725 to 1.9.
Returning to the example of the woman mentioned above with a basal metabolic rate of 1,469 kcal, who exercises three times a week – her total daily expenditure will be approximately 1,469 × 1.55, which is roughly 2,277 kilocalories. This is the amount of energy at which her weight would remain stable. In order to begin losing weight, she needs to create a caloric deficit.
A caloric deficit simply means that the body takes in less energy than it expends. Body fat is an energy store – one kilogram of adipose tissue corresponds to approximately 7,700 kilocalories. For a person to lose one kilogram of fat, they therefore need to create a deficit of exactly this amount over a certain period of time. With a daily deficit of 500 kilocalories, this works out to approximately two weeks per kilogram – and this is the pace that experts describe as safe and sustainable.
This is precisely where most people make a fundamental mistake. They try to lose weight as quickly as possible and set the deficit too aggressively – 800, 1,000, or even more kilocalories per day below their expenditure. This may work in the short term, but the body soon begins to resist. It reduces thyroid hormone production, raises cortisol levels, limits energy expenditure during movement, and begins breaking down muscle tissue as a fuel source. Studies published in the specialist journal Obesity Reviews have repeatedly confirmed that overly strict diets lead to the so-called yo-yo effect – after the diet ends, body weight not only returns but often exceeds the original value.
So how should the deficit be set correctly? Nutrition and sports medicine experts agree that the optimal caloric deficit is between 300 and 500 kilocalories per day. This range allows for weight loss of approximately 0.5 to 1 kilogram per week, while the body has sufficient energy to preserve muscle mass, hormonal balance, and overall health. For the woman in our example, this would mean an intake of approximately 1,750 to 1,950 kilocalories per day – far more than many women would allow themselves to eat, and yet they would still be gradually losing weight.
It is also important to mention that the deficit does not need to be created solely by restricting food intake. Physical activity increases energy expenditure, and therefore also the room for food. A combination of moderately reduced intake and increased physical activity is in fact ideal for sustainable weight loss – it preserves muscle mass, improves fitness, and supports psychological wellbeing. As leading Czech nutritional adviser and author of several books on healthy living Martin Jelínek puts it: "Weight loss is not a punishment, it is an investment in yourself – and like any good investment, it requires patience and reason, not shortcuts."
An integral part of the whole equation is also the composition of the diet. A caloric deficit alone is not enough – what the calories come from also matters. Adequate protein intake (approximately 1.6 to 2.2 grams per kilogram of body weight) is key to preserving muscle mass during weight loss. Complex carbohydrates ensure stable energy levels and prevent mood swings and cravings. Healthy fats are essential for vitamin absorption and proper hormonal function. If you focus only on numbers and ignore the quality of your diet, results will come more slowly and you will feel worse.
Modern technology has made calculations significantly easier today. There are a whole range of apps and online calculators that, after entering basic information, calculate both basal metabolic rate and total expenditure, as well as the recommended intake for weight loss. Popular options include interfaces such as Cronometer or Czech apps focused on dietary tracking. However, it is important to treat these numbers as indicative values rather than absolute truth – every organism is unique and the values can differ from reality by 10 to 20%.
Regular monitoring and adjustment also play a major role. As the body loses weight, its basal metabolic rate changes too – a lighter body needs less energy. It is therefore advisable to recalculate the values approximately every four to six weeks and adjust the deficit accordingly if necessary. It is equally sensible to occasionally incorporate a so-called "refeeding" – a day or two of higher caloric intake, which helps restore the levels of hormones that influence metabolism and appetite, particularly leptin.
Sustainable weight loss is not a sprint, but a marathon. People who approach weight change with an understanding of their own body, with realistic expectations, and without unnecessary haste, achieve results they truly maintain. Petra from Brno, mentioned at the beginning, lost nine kilograms over seven months – more slowly than she had expected, but without a single yo-yo effect. Today, a year and a half after starting, she still weighs the same and says that for the first time in her life she does not feel as though she is "on a diet."
Understanding how the body works, how to calculate one's energy needs, and how to set a deficit that is sustainable in the long term is the most valuable thing a person can do for their health. No diet, no miracle supplement, and no shortcut can replace this basic mathematics. And once a person understands this mathematics, they will find that weight loss is actually surprisingly straightforward.
