The terms “overweight” and “obesity” refer to body weight and body fat content. However, they are not the same. What is behind them, how to distinguish them and on what basis can we say whether the problems they describe concern us?
Obesity and overweight
Obesity is a disease that poses a threat to health and sometimes even life. It is characterized by pathological accumulation of adipose tissue in the body (>15% of the body weight of an adult man and >25% of the body weight of an adult woman), exceeding its physiological needs.
Being overweight should be treated as a prelude to obesity, a warning condition, a warning signal that it is high time to start fighting excess kilograms. How do we recognize that we are dealing with one or the other? The simplest and most commonly used “tool” for this purpose is the BMI index, also called the Quetelet index (after the Belgian mathematician, astronomer and statistician Adolf Quetelet, who proposed its use in 1832).
BMI, or the formula for obesity
BMI (body mass index) is the quotient of body weight expressed in kilograms and height expressed in meters squared:
BMI = kg/m2
To calculate the value of this indicator, it is enough to divide the weight (in kilograms) twice by your height (in meters). For example: if you weigh 60 kg and measure 1.64 m, your BMI is approx. 22.3 kg/m² (60 : 1.64 = 36.6 : 1.64 = 22.3).
BMI scale – from underweight to extreme obesity
Now it’s time to interpret the results. According to the BMI calculator developed on the basis of data from the World Health Organization (WHO), individual BMI values mean:
BMI < 18.5 kg/m² – underweight,BMI 18.5–24.9 kg/m² – normal body weight,BMI between 25.0 – 29.9 kg/m² – overweight,BMI ≥ 30 kg/m² – obesity, with three grades:
I degree – BMI in the range of 30.0–34.9 kg/m²),
Grade II – BMI in the range of 35.0–39.9 kg/m²,
Grade III (known as extreme, morbid, or fatal obesity) – BMI ≥ 40.0 kg/m².
When BMI is not enough
However, the BMI index, popular mainly due to its ease of calculation, has its drawbacks and limitations. It is calculated for an average adult without distinction of sex. BMI does not allow you to estimate the share of body fat in body weight, and what is muscle, bone and water. It also does not take into account the distribution of this tissue, i.e. the type of obesity (abdominal vs. buttock-femoral obesity), which, according to research, plays the most important role in assessing the risk of diseases associated with this disease.
For this reason, the use of a BMI calculator, for example, in athletes and physically active people who have extensive muscle tissue, can lead to incorrect conclusions. The BMI calculator is also not used for pregnant and lactating women, the elderly and children. Growth charts are used to assess body weight in the latter group.
The amount of body fat can be precisely determined using many methods. These include computed tomography (CT), nuclear magnetic resonance (MRI) or dual-energy X-ray absorptiometry (DXA). Due to the limited availability of specialized equipment and high costs, these tests are very rarely done in practice.
Skinfold thickness measurement – electrical bioimpedance (BIA)
Skinfold thickness measurement is much more common, and recently the technique of electrical bioimpedance (BIA) has been used. It is a non-invasive method of body composition testing that measures the electrical resistance of soft tissues through which a low-intensity current is passed. The portable equipment used for this is relatively inexpensive and easy to use, which is why it can be found in doctor’s offices, dietary clinics or even fitness clubs.
A tool for a simple assessment of the type of obesity most of us have at home. It is a tailor’s tape measure, thanks to which we can measure the waist circumference and determine the WHR (waist-hip ratio), which determines the ratio of waist circumference to hip circumference. If it is ≥ 0.8 in ≥a woman and 1.0 in a man, it means abdominal obesity (also known as visceral, android or visceral). Lower WHR values indicate gluteofemoral obesity (also known as gynoid obesity).
If you want to find out if your weight is within the normal range and what type of obesity you tend to, it is worth calculating your BMI and WHR. If their values concern us, a more detailed assessment of body composition, including the content and distribution of body fat in the body, is recommended.