Are We Measuring Metabolic Health Wrong?

For years, “metabolic health” has largely been discussed in terms of body weight, blood sugar and cholesterol. If your BMI was in the healthy range, your fasting glucose was normal and your cholesterol looked reasonable, you might assume that your metabolism was working well. But our understanding of metabolic health is changing.

Research increasingly suggests that metabolic health is much more complex than simply asking “Are you overweight?” or “Is your blood sugar normal?” It involves how effectively different tissues handle nutrients, where fat is stored, how sensitive we are to insulin, the health of our liver and muscles, blood pressure, blood lipids, inflammation, physical activity, sleep and possibly even the timing of our meals.

This doesn't mean that traditional measures such as weight, waist circumference, blood pressure, glucose and cholesterol are unimportant. Rather, they are pieces of a much bigger picture.

What do we actually mean by metabolic health?

There isn't one universally accepted definition of metabolic health.

In practice, clinicians tend to look at a collection of markers including:

• blood glucose and HbA1c

• blood pressure

• triglycerides and HDL cholesterol

• waist circumference or other measures of abdominal fat

• body weight and body composition

• insulin resistance

• liver health

• cardiovascular risk

  
  

The problem is that metabolic dysfunction can develop before these markers become obviously abnormal. For example, insulin resistance can increase for years before someone develops prediabetes or type 2 diabetes. Similarly, fat can accumulate around internal organs and within the liver without necessarily producing obvious symptoms.

This is one reason why researchers are increasingly interested in what is happening inside the body rather than simply what we can see on the scales.

BMI doesn't tell the whole story

BMI is useful at a population level, but it is a relatively crude measure.

It doesn't tell us:

• how much of someone's weight is muscle

• how much is body fat

• where the fat is stored

• whether someone has excess visceral fat

• whether they have fatty liver

• how insulin-sensitive their tissues are

  
  

The 2026 American Diabetes Association guidance therefore recommends that, where feasible, excess adiposity should be assessed using measures such as waist circumference, waist-to-hip ratio or waist-to-height ratio alongside BMI. These measures can provide additional information about metabolic risk.

This helps explain an apparent paradox:

Someone can have a normal BMI but poor metabolic health, while another person with a higher BMI may have relatively good metabolic markers.

Body size is important, but it isn't the same thing as metabolic health.

It's not just how much fat you have — it's where you store it

One of the most important developments in metabolic research is our understanding of fat distribution. Subcutaneous fat, the fat stored underneath the skin, is not necessarily as metabolically harmful as fat accumulating around internal organs.

The more concerning pattern is often visceral and ectopic fat. Visceral fat accumulates around organs in the abdomen, while ectopic fat refers to fat stored in places where it isn't normally supposed to accumulate, including the liver and other organs.

When the body's capacity to safely store excess energy is exceeded, fat can begin to spill over into other tissues. This is associated with insulin resistance, inflammation and other metabolic abnormalities.

This helps explain why two people with exactly the same body weight can have very different metabolic profiles.

Insulin resistance is more complicated than we once thought

Insulin resistance is often described as though it is one single condition,

but different tissues can become insulin resistant to different degrees.

Your muscles, liver and adipose tissue all have different roles in regulating energy metabolism.

Muscle is particularly important because it is one of the major sites for glucose disposal after eating. The liver controls glucose production and plays a central role in lipid metabolism. Adipose tissue acts not simply as a passive storage depot but as an active endocrine organ that releases fatty acids and signalling molecules.

A fascinating study published in 2026 (1) illustrates this complexity. Researchers studying 229 adults found that around 42% had discordant patterns of muscle and adipose-tissue insulin resistance. Importantly, adipose-tissue insulin resistance was associated with a poorer cardiometabolic profile independently of muscle insulin resistance, including greater abdominal fat, higher fasting insulin and triglycerides, greater glycaemic variability, more liver fat and greater hepatic insulin resistance.

This is early evidence rather than the final word, but it highlights an important shift in thinking: Insulin resistance isn't necessarily a single, uniform metabolic problem.

Understanding which tissues are becoming dysfunctional may eventually help us develop more personalised approaches to prevention and treatment.

Your liver is a major player in metabolic health

The liver is central to metabolic regulation.

It helps control:

• blood glucose

• fat metabolism

• cholesterol and lipoprotein production

• glycogen storage

• detoxification and nutrient processing

  
  

When excess fat accumulates in the liver in association with metabolic dysfunction, this is now generally referred to as metabolic dysfunction-associated steatotic liver disease (MASLD) previously called non-alcholic fatty liver disease (NAFLD).

MASLD is increasingly recognised as part of the metabolic disease spectrum rather than simply being a separate liver problem. The 2026 American Diabetes Association Standards of Care (2) emphasise the close relationship between MASLD, insulin resistance, obesity, prediabetes and type 2 diabetes. They also recommend risk assessment for liver fibrosis in people with diabetes or prediabetes who are at increased risk.

And importantly, normal liver enzymes don't necessarily rule out significant liver disease.

This is another example of why metabolic health cannot be reduced to a standard cholesterol or glucose test.

Muscle is a metabolic organ

When we think about muscle, we often think about strength and mobility, but skeletal muscle is also a major metabolic organ.

Muscle tissue is an important site for glucose disposal, and maintaining muscle mass and function becomes increasingly important as we age.

This is one reason why resistance exercise deserves a place alongside cardiovascular exercise when discussing metabolic health.

You don't necessarily need to become a gym enthusiast. Activities such as resistance bands, bodyweight exercises, weights or appropriately adapted strength exercises can all provide a stimulus to muscle.

Metabolic flexibility: can your body switch fuel sources?

Another concept attracting considerable research interest is metabolic flexibility.

In simple terms, metabolic flexibility describes the ability of the body to switch between using different fuels according to circumstances.

After eating, glucose utilisation generally increases. During fasting or prolonged periods without carbohydrate, the body can increase its use of stored fat and ketones.

A metabolically flexible system should be able to adapt to changing fuel availability. This concept is particularly interesting in discussions about:

• fasting

• ketogenic diets

• exercise

• insulin sensitivity

• mitochondrial function

• obesity

• metabolic syndrome

  
  

However, it is important not to overstate the evidence. Metabolic flexibility is an interesting research concept, but it is not currently a simple clinical test that everyone needs to optimise.

Nor does greater ketone production automatically mean better metabolic health.

The more useful question is probably whether the body can appropriately regulate energy storage and utilisation while maintaining healthy glucose, lipid and hormonal responses.

Does meal timing matter?

Traditionally, nutrition research has focused heavily on what we eat.

Increasingly, researchers are also asking when we eat. Our metabolism follows circadian rhythms. Insulin sensitivity, glucose tolerance, appetite hormones and other metabolic processes vary across the day. This has generated interest in areas such as:

• time-restricted eating

• earlier versus later meals

• avoiding large meals close to bedtime

• aligning food intake with circadian rhythms

  
  

The evidence is promising but still developing. Time-restricted eating can be useful for some people, particularly if it naturally reduces late-night eating and overall energy intake. But it isn't a magic metabolic intervention, and it isn't suitable for everyone.

For some people, particularly those with inadequate energy intake, a history of disordered eating, certain medications or chronic illness, aggressive fasting may be counterproductive.

Sleep is part of metabolic health

Sleep is sometimes treated as an optional lifestyle extra. It shouldn't be.

Poor sleep can influence appetite, food choices, glucose regulation, insulin sensitivity and the hormones involved in hunger and satiety.

Chronic sleep restriction may therefore make maintaining metabolic health more difficult, even when someone's diet appears relatively good.

This means that a metabolic-health strategy should not simply consist of:

“Eat less and exercise more.”

It should also ask:

Are you sleeping well?

Are you recovering adequately?

Are you chronically stressed?

Are you sedentary for most of the day?

Are you eating at times that fit your circadian rhythm?

These factors interact with nutrition rather than existing separately from it.

What about diet?

There is no single diet that everyone needs to follow to achieve good metabolic health.

The strongest evidence supports overall dietary patterns that emphasise minimally processed foods, vegetables, appropriate protein, healthy fats, fibre-rich foods and good-quality carbohydrate sources while reducing excess refined carbohydrate, added sugars and highly processed foods.

The 2026 ADA recommendations similarly emphasise nutrient quality, appropriate energy intake and individualised eating patterns rather than prescribing one universal diet.

This leaves room for different dietary approaches. A Mediterranean-style diet can be highly effective. A lower-carbohydrate diet may be particularly useful for some people with insulin resistance or impaired glucose regulation.

A higher-carbohydrate diet can also be metabolically healthy when the carbohydrates come predominantly from minimally processed, fibre-rich foods and overall energy intake is appropriate.

The key is not simply the percentage of carbohydrate, fat or protein.

Food quality, metabolic response, energy balance, satiety, sustainability and individual circumstances all matter.

And what about weight loss?

Weight remains relevant. Excess adiposity, particularly visceral adiposity, is associated with increased risk of insulin resistance, type 2 diabetes, cardiovascular disease and MASLD, but the modern approach is increasingly moving away from viewing weight as the only outcome that matters.

A person can improve their metabolic health without dramatic changes on the scales.

For example, improving diet quality, increasing muscle activity, improving blood pressure, reducing triglycerides or improving glucose regulation may all represent meaningful improvements.

Conversely, losing weight rapidly while losing substantial muscle mass, becoming nutritionally depleted or adopting an unsustainable diet isn't necessarily the definition of metabolic success.

The 2026 ADA guidance recommends an individualised approach to obesity and weight management, incorporating nutrition, physical activity, behavioural support and, where appropriate, pharmacological or surgical treatments.

So how can you assess your own metabolic health?

Rather than focusing on one number, think about your metabolic health profile. Useful measures to discuss with your healthcare professional may include:

Body composition

• BMI

• waist circumference

• waist-to-height ratio

• body composition where appropriate

Glucose regulation

• fasting glucose

• HbA1c

• sometimes fasting insulin or other assessments of insulin resistance

Blood lipids

• triglycerides

• HDL cholesterol

• LDL cholesterol and other cardiovascular risk markers where appropriate

Blood pressure

• resting blood pressure

• trends over time rather than a single reading

Liver health

• liver enzymes

• assessment for MASLD where clinically appropriate

Physical function

• muscle strength

• muscle mass

• physical activity levels

Lifestyle

• sleep quality

• sedentary time

• dietary quality

• alcohol intake

• stress and recovery

  
  

Not everyone needs every test. The appropriate assessment depends on age, symptoms, medical history and individual risk.

The metabolic health checklist

If you want to improve your metabolic health, start with the basics.

1. Build meals around minimally processed foods

Prioritise vegetables, quality protein, nuts and seeds, healthy fats and appropriately chosen carbohydrate sources.

2. Get enough protein

Adequate protein supports muscle maintenance and satiety, particularly as we get older.

3. Look after your muscles

Resistance exercise is an important component of metabolic health — but the amount and type should be appropriate for your health and physical capacity.

4. Reduce highly processed foods

You don't need a perfect diet. But reducing excess refined carbohydrates, added sugars and highly processed foods can make a substantial difference to overall dietary quality.

5. Pay attention to your waist as well as your weight

Changes in waist circumference can provide useful information about abdominal fat that BMI alone cannot capture.

6. Prioritise sleep

Improving sleep may be one of the most overlooked ways of supporting metabolic health.

7. Avoid prolonged sitting where possible

For those who are able, breaking up sedentary time with gentle movement can be useful even when formal exercise isn't possible.

For people with ME/CFS or Long COVID, this needs to be interpreted very differently: activity should remain within individual limits and must not trigger post-exertional malaise.

8. Don't become obsessed with blood glucose

Glucose is important, but metabolic health is much bigger than glucose alone. Look at the whole picture.

The bigger picture

Perhaps the most important change in our understanding of metabolic health is that metabolism is not simply about calories going in and calories going out.

It is a complex system involving the brain, liver, muscles, adipose tissue, pancreas, gut and cardiovascular system. It is influenced by our genes, diet, activity, sleep, stress, age, hormones and environment,

and increasingly, researchers are recognising that metabolic dysfunction can develop long before conventional disease becomes obvious.

This doesn't mean that everyone needs expensive tests, continuous glucose monitoring, supplements or a highly restrictive diet. In fact, the opposite may be true.

The emerging science reinforces the importance of getting the fundamentals right:

eat predominantly nutritious food, maintain muscle, manage excess visceral fat where appropriate, sleep well, stay active within your capabilities, avoid excessive alcohol and highly processed foods, and monitor the key health markers that matter to you.

The exciting part is that metabolic health is increasingly being viewed as something much more nuanced — and potentially much more modifiable — than simply a number on the scales.

The take-home message

Metabolic health isn't a body size. It isn't a blood sugar reading. And it isn't a single blood test.

It is the ability of your body to regulate energy, glucose, fats and other nutrients effectively across multiple tissues and in response to changing demands.

As research continues to uncover the differences between adipose, muscle and liver insulin resistance, the importance of visceral and ectopic fat, the role of muscle, sleep and circadian biology, we are moving towards a much more sophisticated understanding of what it means to be metabolically healthy.

The future of metabolic health may be less about chasing one perfect number — and more about understanding the whole metabolic picture.