Calorie consumption, basal metabolic rate, power metabolic rate - How to determine the ideal calorie amount

How many calories you eat is a decisive factor in whether you gain or lose weight. Determining the ideal amount of calories, however, is not that easy.

In closed systems, energy is constant, according to the first law of thermodynamics. This means that energy does not simply appear out of thin air, nor does it simply dissipate. If we consider the human body as a closed system, it quickly becomes clear what significance this central basic rule of physics has: If the amount of energy is constant, that is, if you add as many calories through your diet as you consume, there will be no change in total energy. The logical conclusion: if you want to lose weight, you have to add fewer calories to the system than you consume. If, on the other hand, you want to gain weight, you need a calorie surplus.

Consider the complexity of the human body!

So far, so simple. But fortunately, the days when people stubbornly based their weight on the body mass index (BMI), i.e. the ratio of body weight to height, as the only relevant parameter, are over. If you take a closer look at the human body, you will quickly realize that it is possible to bring about weight changes outside the guidelines of thermodynamics. This is usually achieved by controlling the water balance. An example: The great initial success of low carb or ketogenic diets is mainly due to the fact that carbohydrates store water in the muscles in the form of glycogen. If you reduce your carbohydrate intake, the amount of stored water also decreases. The result: you lose weight even though you have not changed the amount of calories. Furthermore, it is possible to build muscle and lose fat at the same time through intensive training, although the total amount of energy remains the same.

The consequences would be even more drastic: due to the larger muscle mass, the calorie requirement would increase despite the body weight remaining the same. And then the amount of energy our body has to expend to make the supplied energy usable is not the same for all macronutrients. This is referred to as postprandial thermogenesis. For example, energy consumption increases by only around three percent when fats are consumed, while it rises by five to ten percent for carbohydrates and by as much as twenty to thirty percent for proteins.

Do not overvalue formulas!

What does all this tell us? A stubborn calculation of calorie requirements using formulas is only useful to a limited extent, especially if you do intensive sports. Nevertheless, such formulas are not completely useless. They can be used as an initial guide. The best known formula is certainly the Harris-Benedict formula.

This is for men:

G = (66.5 + 13.7 × body weight in kg) + (5 × height in cm) - (6.8 × age in years).

And for women:

G = (665.1 + 9.6 × body weight in kg) + (1.8 × height in cm) - (4.7 × age in years).

G = (665.1 + 9.6 × 62) + (1.8 × 168) - (4.7 × 29)

G = 1.260,3 + 302,4 - 136,3

G = 1.426,4

The result G thus corresponds to the basal metabolic rate, i.e. the amount of calories that the body needs to maintain its function at an outside temperature of 28 degrees Celsius and at complete rest. However, since our physical activity in real everyday life is different, we have to add the power metabolic rate if we want to determine the total calorie consumption. The PAL value (Physical Activity Level) is used for this purpose. The following table shows by which factor the basal metabolic rate must be multiplied in order to determine the total calorie consumption.

Factor	Activity	Examples
Normal weight	0,95
Overweight	1,2	Bedridden people
Obese	1,4-1,5	Office work at a desk
Normal weight	1,6-1,7	Pupil, student, cab driver
Overweight	1,8-1,9	salesman, craftsman, waiter
Obese	2,0-2,4	Construction worker, competitive athlete

To get the most accurate figures, you should multiply the factors by the number of hours you spend doing that activity. These values are then added and finally divided by 24.

Example:

E

in 23-year-old man with a height of 184 cm and a body weight of 82 kg, according to the Harris-Benedict formula, comes to a basal metabolic rate of:

G = (66,5 + 13,7 × 82) + (5 × 184) - (6,8 × 23) = 2.266,3

He sleeps eight hours a day, goes to university for six hours a day and then works four hours as a waiter. In addition, he does one hour of sports daily. The rest of the time he spends primarily on the couch. For the PAL value, this means:

2,266.3 x 0.95 x 8 = 17,223.8

2,266.3 x 1.4 x 5 = 15,864.1

2,266.3 x 1.6 x 6 = 21,756.5

2,266.3 x 1.8 x 4 = 16,317.4

2,266.3 x 2.0 x 1 = 4,532.6

Adding these values gives 75,694.5. Divided by 24 gives a daily calorie consumption of 3,153.9 calories.

But how accurate is this figure? In any case, it is no more than an approximate value. There are many reasons for this. For one, the calculation of basal metabolic rate does not take into account body composition, that is, the distribution of muscle mass and body fat. While body fat is inert mass, muscle requires energy. So it can happen that twins with identical height and weight nevertheless have entirely different calorie requirements, simply because one has a body fat percentage of seven percent, the other of twenty percent. In addition, the calculation of PAL values is prone to error. In addition, almost no one's day is the same. The PAL values also showed this quite nicely: every increase in activity level significantly increases the amount of calories you can eat each day.

So why all the effort? The calculated calorie consumption is a good basis for accurately determining the actual calorie consumption. So our student from the example could now start to consume the roughly calculated 3,150 calories daily. Whether this amount fits or not will become apparent after some time. If the weight increases, we can assume that the calorie intake is higher than the actual requirement. If, on the other hand, one loses weight, the actual consumption is probably higher than calculated. In order to rule out falsifications due to water retention, which is particularly common in women during the menstrual cycle, it is advisable to weigh oneself daily and to form a weekly average from the values.

Can't it be simpler?

The procedure described is indeed quite complex. However, there are of course ways to simplify it. For one thing, there are now quite precise gadgets that are worn on the body all day and determine calorie consumption with great reliability, completely without formulas and calculations. The catch: these gadgets are usually quite expensive. Less expensive, but less precise: If you keep a precise record of how many calories you consume each day and weigh yourself at the same time, you will soon be able to make a very precise statement about whether the amount of calories you consume is in line with your needs. For this purpose, a weekly average value is taken for calorie intake and weight and this is observed.

What remains is the effort for weighing, but above all for tracking the calories. Although there is now a whole host of apps for this, it is still time-consuming. However, there is hardly any way around this effort. Only very rigid nutrition plans with exact specifications without deviations save you this procedure.

I want to lose weight, how much deficit do I need?

If the goal is weight reduction, a calorie deficit makes sense. In theory, it is possible to lose weight with a balanced calorie intake by building muscle and losing fat, but progress is likely to be marginal. When it comes to the size of the deficit, one should always act according to the principle as much as necessary, as little as possible. Someone who loses weight with a calorie deficit of 200 calories does not need a deficit of 800 calories. Although this would accelerate short-term weight loss, it is not effective in the longer term. Background: Our body is very adaptable. As soon as the energy supplied in the form of calories is no longer sufficient to cover the daily requirement, it takes the difference from the body's own stores. At the same time, however, it also tries to reduce calorie consumption. This can be compared to the power-saving mode of a smartphone or laptop.

The consequence: For further weight loss, the deficit must be further increased. But those who have already largely exhausted their margin at the beginning now face a problem. Because one should go with the calorie supply if at all only very short term under the basic conversion rate. The reason: the higher the deficit, the more the body tends to switch off energy consumers. These are in the body above all also the muscles, which are then literally wegdiätet. But since muscles are very metabolically active, the basal metabolic rate continues to drop and at some point you get into a vicious circle. Also, various bodily functions such as hormone formation are negatively affected. As a rule of thumb, an energy deficit of around ten percent of the daily calorie requirement is therefore a good starting point.

In general, the goal should always be to reduce body fat. Therefore, focusing too much on body weight is often not conducive to achieving the goal. Therefore, in addition to body weight, it is advisable to regularly measure the circumferences of the abdomen and hips to determine the hip-abdominal circumference (HBU). The German Society for Sports Medicine and Prevention (Deutscher Sportärztebund) gives the following guide values for this:

	Women	Men
Normal weight	< 0,8 0,84xtagstartz/td>	> 0,99

Although fat distribution varies widely, a decreasing HBU is a strong indication that body fat has been reduced. Alternatively, body fat can of course be measured. The main methods available for this are caliper measurement and bioimpedance analysis. Caliper measurement can provide quite accurate results, but must be performed by a very experienced person. Bioimpedance analysis is highly susceptible to interfering factors. Therefore, one should not attach too much importance to the absolute values determined. However, if the values are documented, the development over time is quite meaningful.

It should be noted that in most cases the more promising approach is not only to reduce calorie intake, but also to increase physical activity.

I want to gain weight, how much more do I need to eat?

If, on the other hand, you want to gain weight, you generally need more calories. The same principle applies here as for losing weight. There are certainly exceptions. Especially male adolescents with a high sports workload often need immense amounts of calories to gain weight at all. In practice, however, it is much more common to observe cases in which the calorie surplus actually required is massively overestimated. The result: Instead of the hoped-for muscles, one gains mainly body fat. Therefore, even if you want to build mass, you should proceed discreetly and keep an eye on the HBU.

Too complicated?

Granted, of course it is also easier. Eat half should work for most people who want to lose weight, at least temporarily, without calculating, tracking and measuring. And if you simply eat everything you can get your hands on, you're sure to build muscle if you train intensively. Neither is ideal for the reasons described.

The nice thing is that once you have made this effort for some time, you develop a pretty good sense of how much you can or should eat. You can also estimate the calories of different meals much better, so that you can reduce the effort significantly. So there is a learning effect from which you benefit in the long term.