What does body composition really mean? How can you estimate body fat, and which assessment methods are available?

Understanding body composition interests more people than ever, and assessment has become more accessible. Read on for an overview.

What is body composition?

We want to understand the amounts of fat tissue, skeletal muscle, bone, organs and other tissues making up the weight on a conventional scale.

– We often equate gaining or losing weight with gaining or losing fat, but they are not the same.

– Really?

– Depending on training, food and other factors, weight can rise without fat gain, or fall without fat loss.

– Mind blown.

How useful are weight and BMI?

How weight is distributed matters alongside total weight. Weight and BMI alone cannot show whether training or nutritional planning has changed fat, muscle or fluid. BMI does not distinguish these components or fully account for athletic builds. A muscular athlete can fall into an “overweight” category without having excessive body fat.

Neither weight nor BMI alone describes health or fitness. Body composition, strength, mood, performance and sleep can add useful information, without any one measure providing a complete diagnosis.

Body-composition goals also depend on sex, age, sport, playing position and other factors. Body-fat estimates are one tool for monitoring change, rather than a universal target.

How can you estimate body fat?

Imaging and laboratory methods can provide detailed estimates. MRI avoids ionising radiation but requires expensive equipment; no single method is the most accurate for every body component and purpose.

Two practical options are bioelectrical impedance analysis (BIA) and anthropometry. They are more accessible but depend on assumptions and measurement conditions. Which is preferable?

Bioimpedance scales or anthropometry?

In sport, standardised anthropometry is useful for tracking skinfolds and body dimensions. Its accuracy depends on technique and equations; it does not universally outperform BIA. Use a trained practitioner, with recognised training such as ISAK (International Society for the Advancement of Kinanthropometry). Read Anthropometry: what it is, what it measures and why it matters.

BIA can be quicker and performed in light clothing, but its estimates also depend on the population and protocol. Read Scales and bioimpedance for body composition for practical measurement advice and the original article’s scale selection, introduced there as 10 options although only two are described.

At the INDYA centre in Valencia, we choose anthropometry or BIA according to individual needs.