Body mass index (BMI) is a widely used tool for assessing the relationship between a person’s weight and height. Despite its simplicity, it remains a basic reference in nutritional diagnosis and body weight classification. However, its usefulness goes beyond the number: interpreting it correctly can help identify risk factors associated with overweight, obesity or malnutrition.
In this article, we explain in detail what BMI is, how it is calculated, what its values mean, and why in some cases, such as lipoedema, it may be insufficient to reflect the patient’s clinical reality.
Body mass index (BMI) is a measure that allows us to estimate whether a person’s weight is within a healthy range in relation to their height. It is calculated by dividing body weight (in kilograms) by height (in metres) squared:
BMI = weight (kg) / [height (m)]²
Its main use is to provide quick, standardised guidance on an individual’s nutritional status. Based on the values obtained, weight can be classified into categories such as underweight, normal weight, overweight or obese.
Despite being a statistical and indicative tool, BMI is used by international organisations such as the World Health Organisation (WHO) and is present in medical protocols, public health programmes and initial clinical assessments.
BMI was developed in the 19th century by Belgian mathematician and statistician Adolphe Quetelet, who was looking for a simple formula to study human growth in populations. For this reason, it was initially known as the Quetelet index.
Its modern application was consolidated in the 1970s, when the WHO and other organisations adopted it as a screening tool for weight-related health problems. Since then, it has been used in epidemiological studies, medical assessments and global health policies.
However, its use must always be contextualised, as it does not distinguish between fat mass, muscle mass or body distribution, factors that significantly influence an individual’s actual health.
Calculating body mass index is simple, quick and does not require any specialised medical equipment. All you need to know is the person’s weight and height to obtain an approximate value that allows you to classify their nutritional status.
The standard formula for calculating BMI is as follows:
BMI = weight (kg) / [height (m)]²
Where:
This formula has been adopted by the World Health Organisation (WHO) as an international reference for assessing body weight in adults.
Let’s look at a practical example:
A person weighs 70 kg and is 1.65 m tall.
We square the height:
1.65 × 1.65 = 2.7225
We divide the weight by that value:
70 ÷ 2.7225 = 25.7
Result: BMI = 25.7
According to WHO criteria, this person would be classified as overweight (BMI between 25.0 and 29.9).
To facilitate this process, you can use our online BMI calculator available on this page. Simply enter your weight and height, and the system will automatically calculate your body mass index.
In addition, our tool includes an automatic interpretation of the result according to international reference tables, allowing you to know if you are in a healthy range or if there are risks associated with your current weight.
Important: although BMI is useful as a general guide, it is not a substitute for a complete medical evaluation. In specific clinical conditions such as lipoedema, BMI may not reflect the patient’s actual body condition, as we will see later.
Once the body mass index has been calculated, it is essential to interpret its value correctly. To do this, reference ranges defined by international organisations, such as the World Health Organisation (WHO), are used to classify a person’s nutritional status in a standardised way.
According to the WHO, BMI values are grouped into the following categories:
These ranges apply to adults between 18 and 65 years of age. For children, adolescents, or older adults, tables adjusted for age and gender are used.
Each BMI category has important clinical implications:
Correct interpretation of BMI allows for the establishment of evidence-based preventive or therapeutic strategies.
Although BMI ranges are the same for both sexes in adults, there are important physiological differences that must be taken into account:
Therefore, BMI should be used as an initial screening tool, not as a definitive diagnosis.
Although body mass index is a useful tool, its simplicity is also its main weakness. Not all people with the same BMI have the same body composition or health status. Therefore, BMI should be interpreted with caution and supplemented with other assessments when necessary.
BMI does not distinguish between fat mass, muscle mass, body water, or bone density. This can lead to misclassifications in certain profiles:
Furthermore, it does not take into account metabolic and hormonal factors or family history, so it is not reliable as the sole diagnostic measure.
To obtain a more accurate picture of the patient’s nutritional and metabolic status, it is recommended to combine BMI with other body measurements:
Together, these metrics offer a more comprehensive and personalised assessment, tailored to each patient.
Although body mass index is a useful tool in the general population, in specific cases such as lipedema, it can be misleading or even counterproductive if interpreted in isolation. Many patients with lipedema have been incorrectly classified as obese or overweight based solely on their BMI, delaying diagnosis and perpetuating ineffective treatments.
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Lipedema is characterised by a pathological and symmetrical accumulation of subcutaneous fat, especially in the legs and, in some cases, in the arms, but not in the hands, feet or trunk. This fat does not respond to diet or exercise and is accompanied by pain, bruising and progressive functional deterioration.
Since BMI does not assess the distribution or composition of body weight, many patients with mild or moderate lipedema may have a ‘normal’ or slightly elevated BMI and still have advanced disease.
Furthermore, in women with severe lipedema, BMI tends to overestimate obesity without reflecting the real cause of the excess volume: a specific lymphatic and adipose disorder, not a classic caloric or metabolic imbalance.
That is why the joint assessment of BMI together with other parameters such as the Waist-Height Index and the Waist-Hip Index will allow us to more reliably determine whether that accumulation of fat is disproportionate in the extremities and thus support the diagnosis of lipedema.
For example, a patient who has an overweight BMI and a normal Waist-Height Index suggests that the disproportion is in the extremities.
To correctly assess a patient with suspected lipedema, it is essential to go beyond BMI and perform a comprehensive clinical assessment, including:
Only then is it possible to distinguish between common obesity, lymphedema, lipedema, or combinations of these conditions, and to apply a truly effective treatment.
Body mass index is a useful, simple and standardised tool, but it has limitations that must be understood. Using BMI as a starting point is fine, but it should never replace clinical judgement or an individualised assessment of the patient.
In contexts such as lipedema, relying exclusively on BMI can lead to diagnostic errors and therapeutic frustration. That is why at Lipedema Advanced Care we always recommend a multidisciplinary assessment, combining objective tools with clinical experience to offer a truly personalised approach.
