Weight-to-height ratio is one of the most accessible and informative indicators for understanding a person's physical condition and whether there are risks associated with being underweight or, conversely, overweight. This assessment is based on the body mass index (BMI), which provides a basic understanding of how well one's current condition corresponds to physiological parameters.
What is taken into account when assessing physical condition
When assessing a person's physical condition, weight and height aren't the only factors considered. Age, physical activity level, body type, and weight trends also influence the overall assessment of physical health. However, the height-to-weight ratio remains the primary benchmark and the most common reference point. It allows for comparisons between different groups of people and alignment with international recommendations.
What is body mass index?
The body mass index (BMI) is a calculated indicator that helps determine whether a person's weight is appropriate for their height. It is based on a simple mathematical relationship and is used in many countries as a primary benchmark for assessing physical parameters.
While BMI remains the most universal and understandable preliminary assessment method, its interpretation must always take into account its limitations. BMI does not measure muscle mass or fat percentage, does not reflect tissue distribution, and does not take into account individual body characteristics. Therefore, athletes with pronounced muscles may be in the range formally considered overweight, although in practice their condition will be completely normal.
The history of the BMI indicator
This parameter was originally proposed by the Belgian statistician and sociologist Adolphe Quetelet in 1832, and was named the Quetelet index in his honor. Quetelet developed it to calculate the parameters of the average person, whom he defined as a social standard. Initially, the formula was intended for the adult European population and was used primarily in theoretical research.
The origin of the term “body mass index” is attributed to the American physiologist Ancel Keys, who used it in 1972 in one of his studies.
Over time, BMI gained practical significance in medicine. The World Health Organization standardized the indicator's ranges, making them a universal reference for assessing body weight in adults. Today, BMI is used not only to diagnose underweight or overweight, but also to assess the risks of cardiovascular, metabolic, and endocrine diseases.
BMI formula and its practical application
The body mass index formula is based on dividing your weight in kilograms by your height in meters squared. For convenience, you can use online calculators or calculate it yourself—all you need to know is your height and weight. For the formula, your weight remains in kilograms, but your height must be converted to meters.
Height is measured barefoot, standing upright with your back and heels against a wall. It's best to record weight on a flat surface, in light clothing, and at roughly the same time of day to ensure consistent results. However, it's important to remember that BMI is a starting point, and the final assessment should be contextualized, taking into account lifestyle, activity level, health status, and the purpose for which the measurement is being made. BMI is not intended to be used for diagnosis.
BMI values
Once calculated, you can focus on the main categories. International recommendations identify several ranges that reflect a general understanding of the norm. A value below a certain limit may indicate underweight, while values above the norm indicate increased stress on the body.
The world is guided by the following indicators.
1. BMI value (kg/m²): <18.5.
Body weight category: underweight.
Risks: Risk of nutritional deficiencies and health problems
2. BMI value (kg/m²): 18.5–24.9.
Body weight category: normal.
Risks: optimal weight-to-height ratio for health.
3.BMI value (kg/m²): 25–29.9.
Body weight category: overweight.
Risks: Increased risk of cardiovascular and metabolic diseases.
4.BMI value (kg/m²): 30–34.9.
Body weight category: obesity stage 1.
Risks: high risk of concomitant diseases, weight control required.
5. BMI value (kg/m²): 35–39.9.
Body weight category: obesity stage II.
Risks: very high risk of disease, medical correction required.
6. BMI value (kg/m²): ≥40.
Body weight category: obesity stage III.
Risks: extremely high risk, requires comprehensive medical care.
To get a complete picture, you may need additional data, such as waist circumference, body composition, or lab results.
BMI in men and women: what's the difference?
Although the formula for calculating body mass index is the same for men and women, the interpretation of the results may differ. Physiological differences mean that the same value for both sexes does not always reflect the same physical condition.
Men, on average, have more muscle mass and less fat, so their weight may be denser for the same BMI. Women, on the other hand, naturally have a higher percentage of fat, especially in areas related to reproductive function. Hormonal levels also influence results: in women, BMI values can fluctuate depending on age, pregnancy, or menopause. Therefore, gender must be taken into account when evaluating results. A value that is at the upper limit of the normal range for a man may be closer to the middle for a woman.
What to do if your BMI readings are outside the normal range
If your BMI calculation shows that it's outside the normal range, it's time to consider your lifestyle. If you're underweight, consider your diet, including protein sources, vitamins, and minerals. If you're overweight, consider assessing your calorie intake and increasing your physical activity.
A comprehensive approach is essential: changes should be gradual and safe. If significant deviations occur, a consultation with a doctor or nutritionist is recommended to determine a personalized correction plan.
Differences between BMI and other health indicators
• Body fat percentage
This shows what proportion of body mass is made up of adipose tissue. This is important because excess fat, especially in the abdominal area, increases the risk of cardiovascular and metabolic diseases. It is measured in various ways: using bioimpedance scales, skinfold calipers, or more accurate clinical methods such as densitometry (DEXA).
• Waist circumference
Allows you to assess the amount of visceral fat, which envelops internal organs and increases the risk of disease. It is measured standing with a tape measure along the upper border of the pelvic bones or just above the navel. The norm is up to 94 cm for men and up to 80 cm for women; values exceeding these values indicate an increased risk.
• Waist-to-Hip Ratio (WHR)
It shows how fat is distributed throughout the body and is a more accurate indicator of disease risk than weight or BMI alone. Waist and hip circumferences are measured, then the former value is divided by the latter. A WHR above 0.9 in men and 0.85 in women indicates an increased risk of cardiovascular disease.
Together, these indicators provide a much more comprehensive picture of your overall health than BMI alone. They reveal not only your overall weight but also your body composition, the distribution of fat and muscle mass, and potential health risks.
The body mass index remains a simple and accessible tool for a preliminary assessment of one's health. It allows one to determine whether one is within a healthy range and to identify potential risks associated with being underweight or overweight. Using this indicator in conjunction with other methods, one can gain a more accurate understanding of one's health and take timely measures to maintain it within healthy limits.