BMI

Body Mass Index

BMI (Body Mass Index) is a calculation that uses your height and weight to estimate whether your body weight falls within certain population-based categories.

It is calculated as:

weight (kg) ÷ height (m²)

In the UK, BMI categories for adults are generally:-

• Below 18.5 – Underweight
• 18.5 to 24.9 – Healthy weight
• 25 to 29.9 – Overweight
• 30 and above – Obese

It is used in NHS assessments, GP appointments, and health check programmes as a screening tool.

However, it can be misleading as it doesn’t differentiate between muscle and body fat:-

• Muscular people can have a high BMI
• Slim-looking people can have an elevated BMI
• It doesn’t account for body composition

It can influence:-

• Whether you’re offered weight-management support
• Surgical eligibility
• Risk discussions

But it rarely comes with much explanation about its limitations.

For a reluctant patient, that’s where frustration can creep in – the number carries weight (no pun intended), but the nuance often doesn’t.

BMI is useful at a population level. It helps health services identify trends and risks across large groups of people.

But at an individual level, it is:-

• A starting point
• Not a full health assessment
• One indicator among many

It does not measure:-

• Muscle mass
• Fat distribution
• Fitness
• Diet quality
• Mental health
• Metabolic markers

It’s a screening tool – not a complete picture.

From the Case Files