# body weight

The body weight , body mass actually is a biometric feature and refers to the physical mass of a human (or animal), usually expressed in kilograms (kg). It is lowest shortly after birth and then increases steadily along with body size until adulthood with normal development.

Many people, especially in developing countries, are underweight because they don't have enough to eat. Obesity (or its severe form, obesity ) is a common problem that has increased sharply in developing and developed countries.

Also, eating disorders can cause underweight (z. B. anorexia and bulimia ) or lead to obesity (z. B. binge eating ).

In adults, the blood volume is approx. 4.5 to 6.0 liters (approx. 8 percent of body weight (body weight); 77 ± 10 ml / kg body weight in men and 65 ± 10 ml / kg body weight in women).

The skin forms an average of 14 kilograms (excluding the subcutis) and thus makes up around 20 percent of the body's weight. The skeleton makes up twelve percent of the total weight; in a person weighing 75 kilograms, the bones weigh an average of nine kilograms.

## Birth weight

The birth weight of newborns is determined, recorded and statistically evaluated in many countries. There is a correlation between (over) weight of the parturient and (over) weight of the newborn. Being overweight in the womb makes the birth riskier (from 4000 grams the birth risks increase a little, from 4500 grams significantly) and can result in lifelong problems for the newborn.

Overweight women are more likely to suffer from gestational diabetes . Then your blood contains too much sugar. The baby stores the sugar in its organs in a modified form. Although the children grow, they remain immature and often do not achieve the necessary performance.

## Calculation formulas, indices

Body weight can be measured quickly and easily using a scale . A quantitative assessment of body weight in relation to body size is considered problematic. A number of indices have been developed for this purpose over the past 150 years.

### Broca index

The Broca index is a measure for calculating the "normal weight" of a person. It was developed by Paul Broca , a French doctor , surgeon and anthropologist (1824-1880).

Based on the height (in cm ), the index defines a normal weight (in kg ) according to the formula: ${\ displaystyle l}$ ${\ displaystyle m}$

${\ displaystyle m _ {\ mathrm {norm}} = (l-100 \, \ mathrm {cm}) \, {\ tfrac {\ mathrm {kg}} {\ mathrm {cm}}}}$

In the second half of the 20th century, an “ideal weight” of only 90% for men and only 80% for women of the value calculated above was often assumed, but more for aesthetic than medical reasons.

The Broca index allows only a rough estimate and is best for the medium height range; For very tall and very small body sizes, the BMI is somewhat more precise (a limit value analysis can illustrate the limitation: How much can a person with 1 m body size according to Broca weigh? The Broca ideal weight is too low for very small body sizes and too high for very large ones ). From a graphical point of view , the Broca ideal weight is a straight line, depending on body size, the body mass index is a slightly curved curve (parabola).

Because particularities of the respective body structure are not taken into account, both the BMI and Broca index are limited in their informative value; For example, a bodybuilder has a very low percentage of body fat, but may have a BMI of well over 25 due to his high muscle mass.

The advantage of weights calculated according to Broca is that a person who thinks metrically can calculate them in his head.

Example:

For a 1.75 m tall man, the Broca index gives a normal weight of 75 kg and an ideal weight (−10%) 67.5 kg. This corresponds to BMI values ​​of 24.5 or 22, i.e. values ​​within the normal weight range. For a 1.65 m tall woman, the Broca index yields a normal weight of 65 kg and an ideal weight (−20%) 52 kg. This corresponds to BMI values ​​of 24 or 19, i.e. values ​​within the normal weight range. From the age of 65, 2.5 kg are added to the ideal weight for men and women.

### Body mass index

The body mass index (BMI for short), sometimes also called body mass index or number in the German-speaking world , determines an index from the body mass (in kg) and height (in m) using the formula: ${\ displaystyle m}$${\ displaystyle l}$

${\ displaystyle {\ mathit {BMI}} = {\ frac {m} {l ^ {2}}}}$

This is compared with - depending on the source, gender or age-dependent - standard values.

Since it is naturally impossible to differentiate between fat and muscle mass when measuring body weight, the determination of the BMI is often combined with a measurement of the body fat percentage . Nominal overweight in combination with a low body fat percentage indicates a muscular person rather than health-endangering fat. However, it should also be remembered that the load on the hip and knee joints and the lumbar spine is only determined by the weight, regardless of whether the weight comes from shoulder and arm muscles or from abdominal fat pads.

### Ponderal index

The Ponderal Index is similar to the BMI. His formula is:

${\ displaystyle {\ mathit {PI}} = {\ frac {m} {l ^ {3}}}}$

Values ​​between 11 and 14 kg / m 3 are considered normal. This index of the dimension of a mass density almost fulfills the conditions of a dimensionless number of the similarity theory , since it is dimension-analytically independent of the body size and therefore also applicable for children and very tall people. The Ponderal Index is, however, not widely used.

### Waist-to-hip ratio

The waist-to-hip ratio , also known as the waist-to-hip ratio , ignores the relationship between body weight and height and is based solely on body shape. Originally mainly used as an indicator for different health risks with the same BMI, the waist-hip ratio is now also used as the sole indicator of obesity.

### Waist circumference

As a further simplification of the waist-hip ratio , the pure waist circumference , regardless of body size, is used as an indicator of overweight. Because of its simplicity, this method is still favored by many doctors.

### Waist-to-size

The waist-to-height ratio (WHtR), i.e. the waist-to-height ratio, has been discussed since around 2010, which could have a future because of its advantages over the above-mentioned methods for determining healthy body weight. It describes the relationship between waist size and body size and thus also makes a statement about the distribution of body fat and allows greater informative value with regard to the health relevance of obesity (cf. study by Munich Ludwig Maximilians University with over 11,000 test subjects).

The main advantage of the WHtR compared to the BMI is that the BMI only allows a small amount of information about the health-relevant causes of being overweight or underweight , since, for example, very muscular men have a high BMI.

## Normal and ideal weight

Weight classes depending on body mass and height according to BMI data from the WHO

There is no medical consensus as to what the “desirable” or “natural” body weight of a person should be, to be described as normal. It is even debatable whether there is such a value to be determined. In this respect, there are various measurement formulas for determining normal or ideal and under or overweight, which result in similar values. Despite this discussion about the correct value of a normal or ideal weight, there are clear ideas about outside which weight range a person should be judged as (pathologically) underweight or overweight.

A large-scale study by US life insurance companies from the 1950s became particularly well known, in which the body weights with the highest life expectancy were determined - depending on body size, gender and severity of the bone structure - and these were referred to as "ideal weights". For example, the values ​​for a 180 cm tall man with moderate bone structure were 68 to 75 kg (≙ BMI 21 to 23), for a woman of the same height 63 to 70 kg; for a 170 cm tall man 61 to 67 kg, for a woman of the same height 56 ​​to 63 kg. The values ​​were 3 kg higher for heavy bones and 3 kg lower for light ones. For every 10 cm of height, the values ​​increased or decreased by 5 to 6 kg.

In addition to the usual calculation methods, quantiles (for under / overweight) or the median (for the ideal weight ) of empirically obtained distributions of the body weight of a population group are also used for assessment .

A current report by the WHO uses the BMI and defines normal weight with a BMI of 18.5–24.9.

## Underweight

A recent report by the World Health Organization (WHO) uses the BMI and defines underweight with a BMI of less than 18.5.

Underweight (as a result of malnutrition) is often associated with an inadequate supply of protein , fats and carbohydrates as well as vitamins and minerals . The skin and hair change, the bones can decalcify and the muscles shrink. In addition, some organs can no longer do their job properly because of a lack of nutrients .

## Obesity

A WHO report from 2000 uses BMI to define obesity as follows:

BMI
Pre-obesity (overweight in the strict sense) 25-29.9

The health assessment of these limit values ​​is, however, inconsistent among experts. Obesity is a risk factor for various diseases (e.g. heart attack , stroke , diabetes mellitus ). Regular exercise and moderate food (especially low in fat and low in carbohydrates) can reduce body weight.

Some highly regarded but controversial publications suggested that the stated values ​​should be reassessed. According to this, a BMI of 25 to 30 is beneficial for physical health, since people who are slightly to moderately overweight live longer on average, for which the term “obesity paradox” was coined. With some diseases, a higher fat reserve could be beneficial (for example, during surgery or severe infections ). From a statistical point of view, what is called overweight / pre-obesity is the ideal weight, since it is the weight with the highest life expectancy . For example, according to an Israeli long-term study on 10,000 men over 40 years of age, men who are slightly overweight (BMI 25 to 27) have significantly better prospects of longevity than men of normal weight. If you are very overweight (BMI> 27), life expectancy decreases again.

Two publications from 2009 and 2010, in which a large number of studies and meta-analyzes were compared and assessed, show that being slightly overweight is disadvantageous for susceptibility to some diseases and beneficial for others. It also depends very much on where the body fat is stored, if it is in the abdomen ("apple-shaped" figure), this increases the risk of cardiovascular diseases and diabetes . Fat on the buttocks and thighs ("pear-shaped" figure) can protect against precisely these diseases. However, according to current knowledge, the distribution of fat in the body is genetically determined and therefore cannot be influenced, and the risk of osteoarthritis in the joints of the lower extremities is increased by weight, regardless of the fat distribution. The publications mentioned by no means went unchallenged in the professional world.

However, the most comprehensive meta-analysis to date, published in 2016, found that the thesis of “healthy obesity” was not tenable. The “obesity paradox” does not therefore exist; overall mortality is said to be increased in overweight and obese people. Previous studies have not taken into account that some chronic diseases, smoking etc. reduce weight, but increase mortality and thus distort the statistics.

Wiktionary: body weight  - explanations of meanings, word origins, synonyms, translations

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8. ^ Metropolitan Life Insurance Company : Statistical Bulletin. Volume 40, 1959.
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14. Researchers at the Hadassah Hospital in Jerusalem according to a dpa report from January 4, 2007 ( memento of the original from February 10, 2007 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , dpa
15. Association with an increased risk of stroke
16. Short observation period
17. Inappropriate interpretation of the data
18. Main statement not justified
19. Emanuele Di Angelantonio et al .: Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents . In: The Lancet . tape 388 , no. 10046 , August 20, 2016, p. 776-786 , doi : 10.1016 / s0140-6736 (16) 30175-1 .