South Asians and Diabetes: Why It Develops at a Lower BMI

Why can one person carry considerable extra weight and remain metabolically healthy, while another person who looks relatively slim develops fatty liver, insulin resistance or type 2 diabetes?

For South Asians and diabetes, this question is particularly important.

People of South Asian ancestry develop type 2 diabetes at younger ages and often at a lower BMI than many white European populations. A South Asian person can have a BMI that sits comfortably within the conventional “healthy” range and still have significant insulin resistance and metabolic dysfunction.

For decades, we have tended to look at diabetes risk through the lens of body weight.

Perhaps we have been looking at the wrong thing.

The answer may lie not simply in how much fat you carry, but in something far more interesting:

How much fat can your individual body safely store?

Welcome to the fascinating connection between South Asians and diabetes, fat-cell biology, the “thin-fat” phenotype and your Personal Fat Threshold.

Two doctors, the same BMI — and two very different bodies

One of the most memorable illustrations of this problem comes from two doctors: Professor Chittaranjan Yajnik, an Indian physician and diabetes researcher, and his British colleague Professor John Yudkin.

Both men had virtually the same BMI — around 22.3 kg/m².

According to conventional BMI categories, both were comfortably within the “healthy” range.

But when their body composition was measured, something remarkable emerged.

Professor Yajnik had a body-fat percentage of 21.2%.

Professor Yudkin’s was just 9.1%.

Same BMI.

More than twice the percentage of body fat.

The comparison became known as the Yudkin–Yajnik, or Y–Y, paradox.

These were, of course, two individual men, and Professor Yudkin was also a marathon runner. We cannot extrapolate an entire ethnic story from two people.

But their images dramatically illustrated something that larger studies have subsequently confirmed:

BMI does not tell us the whole story.

And when we are talking about South Asians and diabetes, that matters enormously.

Why diabetes can develop at a lower BMI in South Asians

At the same BMI, people of South Asian ancestry tend, on average, to have a higher percentage of body fat and lower lean muscle mass than white European populations.

South Asians are also more susceptible to insulin resistance and type 2 diabetes at lower BMI levels.

This is sometimes described as the South Asian “thin-fat” phenotype.

Someone may not look particularly overweight.

Their BMI may be 22, 23 or 24.

Yet underneath the surface, their metabolic health may tell a very different story.

To understand why, we first need to stop thinking about body fat as simply something bad.

Because healthy fat tissue actually protects us.

Body fat is not simply the enemy

When we eat more energy than our body immediately requires, that energy needs somewhere to go.

Our subcutaneous adipose tissue — the fat stored underneath our skin — provides a relatively safe place to store it.

Think of adipose tissue as a sophisticated metabolic storage organ.

When it is healthy and functioning normally, it stores excess energy as triglyceride inside fat cells, or adipocytes.

Fat tissue can expand in two broad ways.

It can recruit additional fat cells, known as hyperplasia.

Or existing fat cells can become larger as they store more fat, known as hypertrophy.

But there is a limit to how much an individual fat cell can comfortably accommodate.

As adipocytes become excessively enlarged, they can become increasingly insulin resistant and dysfunctional. The surrounding adipose tissue can become more inflammatory, and its ability to safely buffer excess energy begins to deteriorate.

But the incoming energy does not simply disappear.

It has to go somewhere.

And this brings us to one of my favourite ways of explaining the Personal Fat Threshold.

Imagine the wardrobe in your bedroom

Imagine everyone has a bedroom.

And inside that bedroom is a wardrobe.

Some people have an enormous walk-in wardrobe.

They can keep buying clothes and putting them away.

Another shirt?

No problem.

Another dress?

Plenty of room.

Another pair of shoes?

Put them on the shelf.

Everything remains neatly stored where it belongs.

But someone else has a much smaller wardrobe.

There is absolutely nothing wrong with that wardrobe.

It simply has less storage capacity.

Now imagine that both people keep shopping.

The person with the enormous wardrobe continues putting everything neatly away.

But the smaller wardrobe becomes full much sooner.

At first, we squeeze in another shirt.

Then we cram another dress onto the rail.

We push things onto already overflowing shelves.

Eventually, the doors barely close.

But here’s the problem.

We don’t stop shopping just because the wardrobe is full.

The deliveries keep arriving.

So where does everything go?

On the chair.

On the bed.

Under the bed.

Eventually, all over the floor.

The clothes aren’t necessarily the problem.

The problem is that they are now being stored in places that were never designed to store them.

Our bodies can behave in a remarkably similar way.

Your subcutaneous fat is your metabolic wardrobe

Your subcutaneous adipose tissue is like your metabolic wardrobe.

It is designed to store excess energy relatively safely.

But the size and expandability of that wardrobe vary enormously between individuals.

Some people appear able to expand their subcutaneous fat stores considerably before developing major metabolic problems.

Others reach their safe storage capacity much sooner.

When that happens, excess fat can increasingly accumulate in places where we do not want it:

the liver,

around the abdominal organs,

within and around skeletal muscle,

and potentially within the pancreas.

This is called ectopic fat, and it is strongly associated with insulin resistance and metabolic dysfunction.

The clothes have escaped the wardrobe and are now cluttering the rest of the room.

What is the Personal Fat Threshold?

Professor Roy Taylor developed the concept of the Personal Fat Threshold to help explain why type 2 diabetes can occur in people who do not have obesity.

The idea is surprisingly simple.

Each person appears to have an individual threshold beyond which additional fat accumulation becomes metabolically harmful.

That threshold differs from person to person.

One person may gain considerable weight while continuing to store much of that energy in relatively safe subcutaneous fat.

Another may gain only a relatively small amount before their safe storage capacity is exceeded.

Their metabolic wardrobe fills earlier.

And importantly, your Personal Fat Threshold is not determined by whether society considers you overweight.

It isn’t a particular dress size.

It isn’t BMI 25.

And it isn’t BMI 30.

It is your body’s own biological threshold.

Could the South Asian metabolic wardrobe fill sooner?

This is where the Personal Fat Threshold becomes particularly relevant to South Asians and diabetes.

Research suggests that South Asians may differ not simply in how much body fat they carry, but in how that fat is stored.

At comparable BMI levels, studies have found differences including larger abdominal fat cells, greater visceral and liver fat, and lower lean mass in South Asians compared with white Europeans.

There is also evidence suggesting differences in the ability of adipose tissue to continue expanding safely.

If fewer new fat cells are recruited when additional storage is required, existing adipocytes must accommodate more.

They become larger.

Eventually, that safe storage system begins to struggle.

This could be one reason why a South Asian person does not necessarily need to develop visible obesity before metabolic dysfunction appears.

Their BMI may look reassuringly “normal.”

Their metabolism may tell a different story.

But where did this South Asian body composition come from?

This is where the story becomes even more fascinating.

Archaeological research examining South Asian skeletal remains spanning thousands of years suggests that relatively low lean mass for stature has deep roots in South Asian populations.

But there is an interesting twist.

Some ancient South Asian hunter-gatherers were tall and skeletally robust — bodies reflecting lives of considerable physical activity.

Then, as populations transitioned towards settled agriculture, stature declined substantially.

This pattern was not unique to South Asia. Across many ancient populations, the transition to agriculture brought profound changes in diet, activity, infection, population density and living conditions.

The important point is that there probably isn’t one single explanation for the South Asian body type we see today.

It appears to be the result of a very long interaction between ancestry, nutrition, growth, development and environment.

And another clue comes from studying South Asian babies.

The South Asian diabetes story may begin before birth

Professor Yajnik’s research found something fascinating when Indian babies were compared with white European babies.

The Indian babies tended to be smaller.

Measurements reflecting muscle and abdominal organ size were particularly reduced.

Yet their subcutaneous fat was relatively preserved.

Professor Yajnik famously described this as the “thin-fat” Indian baby.

Smaller body.

Less lean tissue.

Yet relatively preserved body fat.

This tells us something important.

Some aspects of the South Asian metabolic phenotype may begin long before adulthood.

Maternal nutrition and metabolic health, fetal growth, childhood nutrition, genetics and the environment in which we grow can all influence the body we eventually develop.

So the metabolic problems appearing at 40 or 50 may have roots reaching all the way back to early life.

And then that body meets a very different world.

Ancient biology meets a modern environment

For most of human history, food required effort to obtain.

People walked.

Carried.

Dug.

Farmed.

Gathered.

Prepared food from basic ingredients.

Daily life itself repeatedly challenged muscle.

Food was also not continuously available.

Now consider our modern environment.

Food is everywhere.

Refined carbohydrates and ultra-processed foods are readily available.

We can eat from the moment we wake until shortly before we sleep.

And many of us spend most of the day sitting.

Our environment has changed extraordinarily quickly.

Our biology has not.

This creates what we might call a metabolic mismatch.

Our metabolic capacity — our muscle mass, fat-storage capacity, liver and pancreatic function and other biological characteristics — has to cope with a metabolic load that can be very different from anything previous generations experienced.

For someone with a lower Personal Fat Threshold and less muscle, that mismatch may become apparent much sooner.

And sometimes at a surprisingly low BMI.

“But my grandparents ate rice three times a day”

This is a question I hear all the time.

And it is a reasonable one.

Rice was part of the diet of many previous South Asian generations.

But rice was only one part of a completely different lifestyle.

Previous generations often moved much more.

Many performed physical work.

Food was less processed.

Constant snacking was uncommon.

Meals were generally prepared from basic ingredients.

And daily life demanded far more from their muscles.

We cannot take one component of an ancestral diet — rice — transplant it into a completely different twenty-first-century lifestyle, and assume the metabolic consequences will be identical.

Context matters.

Muscle: another important part of the South Asian story

The wardrobe helps us understand fat storage.

But there is another side to this story.

Muscle.

Skeletal muscle is one of the body’s major sites for glucose disposal.

After we eat, muscle provides an enormous place for glucose to go.

South Asian populations tend, on average, to have lower lean muscle mass than white European populations.

Modern sedentary living can amplify that disadvantage.

And as we move through midlife and beyond, we naturally begin losing muscle unless we actively work to preserve it.

So we can potentially have two metabolic challenges occurring together:

less capacity to safely accommodate excess fat,

and less metabolically active muscle available to use glucose.

This is why resistance training deserves a much bigger place in the conversation about South Asians and diabetes.

Building muscle isn’t simply about looking toned.

Muscle is metabolic protection.

Why a “normal” BMI doesn’t always mean low diabetes risk

Imagine a South Asian woman sitting in her doctor’s office.

Her BMI is 23.

She has been told for years that her weight is “normal.”

But her waist circumference has gradually increased.

Her triglycerides are rising.

She has fatty liver.

Her blood pressure is creeping upwards.

Her glucose is now in the prediabetes range.

Should we reassure her because her BMI is normal?

Of course not.

Her metabolic warning lights are flashing.

She may already have crossed her Personal Fat Threshold.

This is why we need to look beyond BMI in South Asians.

Waist circumference, blood pressure, glucose, triglycerides, liver health, muscle mass and family history may tell us far more about metabolic risk than weight alone.

The good news: we can change the metabolic load

Understanding our biology should not leave us feeling powerless.

Quite the opposite.

We cannot choose the metabolic wardrobe we were born with.

But we can influence what we keep putting into it.

Professor Taylor’s research has shown that reducing excess body fat can substantially reduce ectopic fat within the liver and pancreas and, particularly earlier in type 2 diabetes, can sometimes restore glucose regulation towards normal.

Think again about that bedroom.

When the deliveries slow down and we begin removing the excess clothes, the floor starts to clear.

The chair appears again.

Eventually, there is space in the wardrobe.

And we can do something else.

We can build muscle.

For South Asians, that may be particularly important.

In practical terms, this means prioritising protein, eating plenty of non-starchy vegetables, reducing refined carbohydrates and ultra-processed foods, avoiding constant eating and snacking, moving regularly, resistance training, sleeping well and managing stress.

It does not mean abandoning rice, curry or the foods that connect us to our families and culture.

It means understanding the body we have and working with it.

Your metabolic wardrobe is yours

Your friend may be able to carry considerably more weight than you without developing the metabolic problems that appear in your body after gaining just a few kilograms.

That does not mean you have failed.

Your bodies are simply not identical.

Genetics, ancestry, early-life development, muscle mass, age, sex, hormones and lifestyle all influence where our individual threshold lies.

There is no universal weight at which every human suddenly becomes metabolically unhealthy.

And there is no universal BMI that tells us everything we need to know.

Perhaps, then, we have been asking the wrong question.

Instead of simply asking:

“Am I overweight?”

Perhaps we should also be asking:

“Has my metabolic wardrobe become full?”

Because for South Asians and diabetes, sometimes the earliest warning isn’t what you see in the mirror.

It is what is happening quietly inside your metabolic wardrobe.

Resources

Learn more about why South Asian’s are at higher risk of metabolic disease HERE

Get your free printable Healthy Eating Habits check list and Healthy Lifestyle Habits checklist

Get your free printable Key Health Measurements check list 

Read Dr Nelum’s Journey to Better Health HERE

Enroll in the South Asian Solutions: Healthy Habits for a Healthy Life online course – a culturally tailored, self-guided program designed to help you prevent and manage metabolic health issues while enjoying the foods you love. 

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