BMI 2025: understanding it, reading it, acting on it for lasting health

Introduction

BMI 2025: should we still rely on the body mass index in 2025? Created nearly two centuries ago, BMI is still used everywhere: in medical check-ups, in public health campaigns, even in online nutrition calculators. Yet its limits are known, and new alternatives are appearing. So why does BMI remain a reference? How do you really understand it, and above all, what do you do with that information once you know your BMI? This article offers a clear exploration, based on recent research, to help you read your body better through this index, with practical advice for adjusting your BMI if needed, naturally and lastingly.

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What exactly is BMI?

BMI stands for body mass index. It is used to estimate an adult's build from two simple measures: height and weight. The formula is:

BMI = weight (in kilos) / height squared (in metres)

This calculation gives a single figure. According to that figure, a person can be placed in a category: underweight, normal weight, overweight or obese. This scale has been defined by the World Health Organization (WHO) since 1997:

• Under 18.5, underweight
• Between 18.5 and 24.9, normal build
• Between 25 and 29.9, overweight
• From 30 upwards, obesity

The index was devised in the nineteenth century by Adolphe Quetelet, a Belgian statistician. His original aim was not medical but sociological: he was trying to establish an "ideal" average build across the population. It was only much later, in the twentieth century, that doctors took up this calculation to assess the risks linked to being overweight. BMI 2025.

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How is BMI calculated?

BMI rests on a simple mathematical principle: weight is set against the surface of the body. By dividing weight by height squared, the effect of being tall on body mass is neutralised. So a person of 60 kg at 1.60 m will have the same BMI as a person of 75 kg at 1.77 m, provided the weight over height squared ratio is equivalent.

A concrete example:

• A woman of 60 kg at 1.65 m gives BMI = 60 / (1.65 x 1.65) = 22.04
• A man of 90 kg at 1.85 m gives BMI = 90 / (1.85 x 1.85) = 26.29

In the first case, the BMI indicates a normal build. In the second, it signals mild excess weight.

This tool is quick, free and usable by everyone. It remains one of the most consulted health indices on the internet.

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Why BMI is still relevant in 2025

Despite the criticism, BMI is still used because it makes it possible to detect health risks at scale. Many studies confirm that the higher the BMI, the higher the risks of cardiovascular disease, type 2 diabetes, joint problems and certain cancers.

Another important point: BMI is used to track major public health trends. It helps health authorities identify at-risk populations, set medical priorities and design effective prevention campaigns.

In practice it also opens a dialogue between patient and health professional. A doctor who sees a high BMI can suggest a fuller assessment, or personalised advice.

Be careful, though: BMI does not tell you everything. You need to read it with some distance and, above all, never interpret it on its own. That is what we look at next.

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The limits of BMI

BMI is simple, but it sometimes simplifies too much. It does not distinguish between different body masses. A very muscular athlete can have a BMI of 28 or 29, and so be considered overweight, when they have not a gram of surplus fat. Conversely, someone with little muscle but a lot of body fat can have a "normal" BMI without being in good health.

Another limit: BMI takes no account of how fat is distributed. Yet where the fat sits is essential. Abdominal fat in particular is far more dangerous to metabolic health than fat on the thighs or arms.

Recent studies also show that the thresholds used to interpret BMI do not adapt well to every ethnic background or every body shape. Some populations show increased risk at lower BMIs, others at higher values.

Finally, BMI does not measure a person's actual metabolic state. It says nothing about inflammation, tissue quality or hormonal balance. It is a broad indicator, useful across a population but insufficient at the individual level.

Modern alternatives to BMI

Faced with the limits of BMI, several complementary measures are used today. They give a finer picture of body composition and of health risks.

1. Waist circumference

Measuring waist circumference (at the navel, without pulling the stomach in) makes it possible to assess visceral fat. A waist over 94 cm in men or 80 cm in women signals excess abdominal fat, even with a "normal" BMI.

2. Body fat index

This assesses the percentage of fat mass in the body. It can be estimated with bioimpedance scales, or more precisely with medical devices (scanner, DEXA and so on). A high body fat index with a normal BMI reveals a "thin outside, fat inside" profile, known as TOFI.

3. The bioimpedance scale

It sends a very weak electrical current through the body and measures the resistance. This makes it possible to assess the split between lean mass, fat mass and body water. It is useful for tracking a physical transformation, but the results can vary with hydration, body temperature or the model used.

4. The SBSI (Surface-Based Shape Index)

More recent, this index combines several measures (height, weight, waist, estimated body surface) to assess metabolic risk more finely than BMI. It is still little used in everyday practice but is the subject of a good deal of research.

🧠 The hidden side of the numbers

A BMI can look "perfect", and yet a person can be living with silent metabolic syndrome. Conversely, someone classed as "overweight" can have an excellent metabolic profile, high vitality and no inflammatory markers.

Numbers do not replace listening to the body. Chronic fatigue, abdominal storage, sleep problems, cravings, prolonged stress: all these bodily signals often say more than a single index.

The future of prevention lies in reading the body in several ways, well beyond the standard figures. BMI 2025.