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In the modern world, an extremely high value, both for aesthetic and health reasons, is attached to… weight. We often wonder if our body weight is correct or if our shapes are within the normal range.
Numerous specialists in medicine, sports, healthy eating and public health are also concerned with these issues. For their needs, many methods have been developed to assess the correctness of the structure, proportions and composition of the human body.
A well-known method is the assessment of the body mass index, or BMI for short. It indirectly determines the degree of excess or deficiency of adipose tissue in the body by determining the ratio of body weight and height.
The BMI value can be easily and quickly calculated from the following formula:
BMI = body weight (kilograms) / height (meters) 2
The obtained result is in one of the four main ranges:
- <18,5 — niedowaga
- 18,5 – 24,9 – correct weight
- 25 – 29,9 – overweight
- > 30 – obesity
In addition, the category of extreme obesity, morbid obesity when BMI exceeds 40 and extreme underweight when BMI is lower than 15. As can be seen from the above list, the range of norms in relation to body weight is quite wide. For example, for a person with a height of 170 cm, both 53,5 kg and 72 kg weight will be considered in terms of the correct weight. And that’s almost 20 kg of difference!
The BMI index is used to roughly assess the amount of adipose tissue in the body and the associated risk of developing cardiovascular, osteoarticular diseases, diabetes and some cancers. Numerous studies have proved that there is a correlation between the excessive amount of fat and the increased incidence of these civilization diseases. Too low amount of adipose tissue (as in the case of patients with anorexia) may also cause health problems, e.g. hormonal disorders, difficulties in getting pregnant.
What is the advantage of using BMI, i.e. the ease and speed of obtaining a result by specifying only two easily measurable parameters, is also its disadvantage. The BMI index does not take into account other variables, it is not modified due to, for example, gender, age, build and body structure, hence its use is limited, and the obtained results do not always reflect reality.
Body weight is not just a simple growth function, it also depends on the amount of muscle tissue and bone mineral density. The decrease or increase in weight does not have to result only from a change in the amount of adipose tissue (it would be difficult to define a muscular bodybuilder as obese), therefore the statement of a given BMI value does not clearly mean belonging to a specific “weight” category, but rather this affiliation suggests and obliges to take into account and analyze the other factors mentioned above. Due to the imperfection of the method, the body mass index should be determined with caution in the elderly (due to the often accompanying osteoporosis), infirm (muscular atrophy) and people with an athletic body structure (large amount of muscle tissue). BMI is not calculated for pregnant women and children and adolescents. The latter use special scales, the so-called percentile grids, which make it possible to relate the child’s weight to his height against the background of peers of the same sex, which is more accurate and reliable than basing on the two-dimensional BMI scale. A child with a body mass index below the 15th percentile is underweight and above the 85th percentile overweight (such a percentile value means that 85% of children of that age and gender have lower weight than the child in relation to their height).
The level of overweight or underweight can also be estimated using the modified body mass index – BMI Prime. It is calculated by dividing a person’s BMI by the BMI value which is the upper limit of the norm, ie 25. If the obtained number is within the range of 0,74 to 1, the weight is within the normal range. Value below 0,74 is underweight, above 1 is overweight. The result can be translated into an estimated percentage of excess / deficiency of adipose tissue, eg BMI Prime 1,2 means 20% excess body weight. The BMI Prime indicator allows, for example, a doctor to visually show the problem of overweight in his patient and quickly calculate how many kilograms he should lose so that his weight returns to normal.
In medicine, simple methods of measuring the waist circumference or waist and hips are also used to determine the risk of developing overweight and obesity-related diseases. Abdominal obesity, which is the main component of the metabolic syndrome, is when the waist circumference in women exceeds 80 cm and in men it exceeds 94 cm (values adopted for Europeans, in the United States these values are 88 cm for women and 102 cm for men, respectively). A waist / hip ratio (obtained by dividing the waist circumference in cm by the hip circumference in cm) greater than 0,85 in women and 0,90 in men is also an indicator of abdominal obesity. On the basis of many scientific studies, it has been found that the fat deposited on the abdomen and around the abdominal organs (the so-called visceral fat) is more dangerous than that accumulated in other areas of the body, e.g. on the thighs or buttocks. Hence, it is not the determination of overweight or obesity using the BMI index as much as the determination of the body type (“apple”, “pear”) and the distribution of adipose tissue is important for the full assessment of the risk of developing cardiovascular diseases and type 2 diabetes.
With the help of more or less advanced technologies, using the differences in the physical properties of muscle, fat and bone tissue, the percentage of fat in the total body weight can be calculated. In moderately physically active people, this indicator ranges from 25 to 31% in women and from 18 to 24% in men. Higher values indicate overweight and obesity, lower values characterize athletic people.
Approximately the percentage of adipose tissue can also be calculated using the BMI using the following formula:
Body weight% fat = (1.20 × BMI) + (0.23 × age) – (10.8 × gender) – 5.4
* gender – women put the value 0, men 1
The BMI body mass index is a useful but imperfect tool for assessing the correctness of body weight and the risk of developing civilization diseases caused by an excessive amount of adipose tissue. In combination with the other indicators described above, it presents more complete, more reliable and reliable results, allowing for better capturing of people at risk of cardiovascular diseases and diabetes.
Calculate your BMI
Author: lek. med. Aleksandra Czachowska