Metabolic Health Beyond BMI: What I Actually Measure in Primary Care

BMI is probably the number we most commonly associate with weight and health. It is quick, inexpensive and useful, but in my day-to-day work as a GP, I would never use BMI alone to decide whether somebody is metabolically healthy.

I see patients with a BMI within the traditional “healthy” range who have hypertension, central adiposity, dyslipidaemia or rising blood glucose. Equally, two people with exactly the same BMI can have very different cardiometabolic risk profiles.

For me, BMI is a starting point. The more important question is: what is happening metabolically, and where is this patient's health heading?

Look beyond the scales

BMI has limitations. It does not tell us where somebody carries their weight, distinguish fat from muscle, or directly measure central adiposity.

One measurement I think we could use more routinely in primary care is waist-to-height ratio.

NICE recommends using waist-to-height ratio alongside BMI in adults with a BMI below 35 kg/m². It gives patients an incredibly simple message too: aim to keep your waist circumference to less than half your height.¹

This matters because central adiposity is associated with increased risks including type 2 diabetes, hypertension and cardiovascular disease.¹

It is a useful example of why someone can have a BMI that appears reassuring while still carrying metabolic risk.

What do I actually measure?

When I am assessing metabolic health, I am trying to build a picture rather than looking for one definitive number.

My assessment will vary according to the patient, their history and existing conditions, but I commonly consider:

• BMI and weight trajectory
• Waist circumference and waist-to-height ratio
• Blood pressure
• HbA1c
• Lipid profile
• Alcohol use
• Diet and physical activity
• Family history of type 2 diabetes and premature cardiovascular disease
• Existing conditions and medications

I also consider the patient's overall cardiovascular risk. For appropriate patients, QRISK3 can be much more meaningful than simply telling someone that their cholesterol is “a little high”.³

The important part is putting all of this information together.

A rising HbA1c alongside increasing waist circumference, hypertension and an adverse lipid profile tells me much more about someone's metabolic health than BMI in isolation.

HbA1c: don't wait for diabetes

One of our biggest opportunities in primary care is identifying deteriorating metabolic health before established disease develops.

HbA1c is particularly useful because it reflects average blood glucose over approximately the previous eight to 12 weeks.

An HbA1c of 42–47 mmol/mol is considered high risk for developing type 2 diabetes. An HbA1c of 48 mmol/mol or above may indicate diabetes and, in an asymptomatic patient, requires appropriate repeat testing to confirm the diagnosis.²

That 42–47 range is important.

I don't want patients to interpret it as: “I'm not diabetic, so everything is fine.”

Instead, it creates an opportunity for a different conversation: your blood glucose is moving in the wrong direction, so what can we change now?

That may involve structured lifestyle support, dietary changes, increasing physical activity, weight management and addressing other cardiovascular risk factors. NICE recommends at least annual blood testing for people at high risk in this range, alongside reviewing weight and lifestyle changes.²

What do I do with the results?

This is where metabolic assessment becomes clinically useful.

There is little benefit in measuring numerous biomarkers if we simply file the results as “satisfactory” or “abnormal”.

I try to explain the findings to patients as an overall picture and, importantly, a trajectory.

If blood pressure is elevated, we address it. If cardiovascular risk warrants intervention, we discuss lifestyle measures and, where indicated, lipid-lowering treatment. If HbA1c is rising, we discuss diabetes prevention. If excess weight or central adiposity is contributing to risk, we discuss appropriate evidence-based weight-management interventions.

We should not wait for weight loss before treating other risk factors. If we identify hypertension, dyslipidaemia or dysglycaemia, these need appropriate management in their own right.¹

Treatment also needs to be individualised. Metabolic health is influenced by far more than weight alone, including genetics, ethnicity, age, medication, sleep, physical activity, diet, smoking, alcohol and existing medical conditions.

Success should mean more than kilograms lost

This is another area where I think our language needs to evolve.

When someone is trying to improve their metabolic health, weight can be an important outcome, but it should not be the only outcome.

I want to know: Has their waist circumference reduced? Has their HbA1c improved? What has happened to their blood pressure and lipid profile? Are they more physically active? Are the changes sustainable?

Someone can make clinically meaningful improvements to their health even when the change on the scales is relatively modest.

Equally, substantial weight loss should not automatically lead us to assume that every other risk factor has resolved. We still need to measure.

Primary care is ideally placed to do this

One of the great advantages we have in general practice is longitudinal care.

We often have years of weight measurements, blood pressure readings, blood results, prescriptions and diagnoses available to us. Individually, these are data points. Viewed together, they can show us a trajectory.

BMI remains useful, and I am certainly not suggesting that we abandon it.

But BMI should prompt a conversation rather than end one.

When I assess a patient's metabolic health, the question I want to answer is not simply:

“What is their BMI?”

It is:

“What is their metabolic risk today, where is it heading, and what can we do now to change that trajectory?”

That, to me, is a much more useful definition of metabolic healthcare in primary care.

Download the cheat sheet

References

1. National Institute for Health and Care Excellence. Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity.
2. National Institute for Health and Care Excellence. Type 2 diabetes: prevention in people at high risk (PH38).
3. National Institute for Health and Care Excellence. Cardiovascular disease: risk assessment and reduction, including lipid modification (NG238).

About the author

Dr Saira Bano is a UK GP with a particular interest in obesity, metabolic health and preventative medicine. Alongside her work in NHS general practice, she is Co-Founder of SwiftDoctor, a GP-led online healthcare and pharmacy service. She has a particular interest in helping patients understand obesity as a chronic, multifactorial condition and in improving the identification and management of cardiometabolic risk in primary care.