Why BMI 25 Can Matter in Thailand: What Asian Obesity Research Shows

If you have ever checked your BMI using an international calculator, you may have seen a BMI of 25 described as “overweight” rather than obesity.

But in Thailand and several other Asian countries, the picture is different.

Asian populations can develop higher levels of body fat and visceral fat at lower BMI levels compared with many European populations. Because of this, metabolic risks such as high blood sugar, high blood pressure, abnormal cholesterol, and obesity-related disease may appear earlier.

This is one reason local guidance in Thailand uses lower BMI thresholds. In the STEP 11 clinical trial, obesity was defined as BMI ≥25 kg/m² in line with local guidance for Thailand and South Korea.

The study gives useful insight into how weight, waist circumference, blood sugar, blood pressure, and other metabolic markers can change in Asian adults receiving structured medical weight-management treatment.

What Does BMI 25 Mean in Thailand?

BMI stands for body mass index. It is calculated using a person’s weight and height and is commonly used as a screening tool for weight-related health risk.

According to the STEP 11 paper, local guidance in Thailand and South Korea uses:

• BMI ≥23 kg/m² for overweight
• BMI ≥25 kg/m² for obesity

These thresholds are lower than the commonly used Western obesity threshold of BMI ≥30 kg/m².

The reason is that BMI does not measure body fat directly. Two people with the same BMI may have very different amounts of body fat, muscle mass, and visceral fat.

For many Asian adults, metabolic risk can rise at a lower BMI than expected.

Why Asian Populations May Face Higher Risk at Lower BMI

The STEP 11 researchers explain that Asian populations tend to accumulate more body fat, particularly visceral adipose tissue, at the same BMI compared with European populations.

Visceral fat is the fat stored deeper around internal organs. It is different from the fat directly under the skin and is more strongly associated with metabolic conditions.

Higher visceral fat levels may contribute to:

• Insulin resistance
• Prediabetes
• Type 2 diabetes
• High blood pressure
• Abnormal cholesterol
• Cardiovascular risk

This means a BMI that looks only mildly elevated on paper may still be associated with meaningful health risk.

BMI Is Useful — But It Is Not the Whole Story

BMI is a convenient starting point, but it does not tell a doctor everything about metabolic health.

Other measurements may provide important information, including:

• Waist circumference
• Blood pressure
• HbA1c
• Fasting blood glucose
• Cholesterol and triglycerides
• Liver function
• Family history
• Body composition
• Existing weight-related conditions

In STEP 11, the average BMI at baseline was 31.3 kg/m², but the trial also included people with BMI between 25 and 30.

The researchers specifically analysed a subgroup with baseline BMI below 30 kg/m² to understand whether the findings also applied to patients who would not necessarily meet the Western definition of obesity.

What Was STEP 11?

STEP 11 was a randomised, double-blind, placebo-controlled phase 3 trial conducted across 12 clinical sites in Thailand and South Korea.

The trial included 150 Asian adults without diabetes who had:

• BMI ≥25 kg/m²
• At least one previous unsuccessful weight-loss attempt

Participants were randomly assigned to receive either semaglutide 2.4 mg once weekly or placebo.

Both groups also received lifestyle support involving a reduced-calorie diet and increased physical activity.

The treatment period lasted 44 weeks.

What Did the Study Find?

Participants receiving semaglutide experienced a significantly larger average reduction in body weight compared with placebo.

At week 44:

• Mean body-weight change was −16.0% with semaglutide
• Mean body-weight change was −3.1% with placebo

The study also found that:

• 96% of semaglutide participants lost at least 5% of body weight
• 78% lost at least 10%
• 53% lost at least 15%
• 30% lost at least 20%

These results were substantially higher than in the placebo group.

It is important to remember that clinical trial averages do not predict individual results. Treatment response can vary considerably from one person to another.

What Did STEP 11 Show in People With BMI Under 30?

This is one of the most interesting findings for patients in Thailand.

The study included 68 participants with a baseline BMI below 30 kg/m².

Among this subgroup:

• 45 received semaglutide
• 23 received placebo

After 44 weeks, average body-weight change was:

• −17.6% with semaglutide
• −4.4% with placebo

The results were broadly similar to those seen in the full trial population.

This is important because it shows that clinically meaningful weight changes were also observed in participants whose BMI was below the traditional Western obesity threshold of 30.

However, this should not be interpreted as meaning that everyone with BMI 25–29 should use medication.

Treatment decisions need to consider overall health risk.

Waist Circumference Also Improved

Waist circumference is an important measurement because it gives additional information about abdominal fat.

At the start of STEP 11, mean waist circumference was 98.1 cm.

By week 44:

• Semaglutide group: average reduction of 11.9 cm
• Placebo group: average reduction of 3.0 cm

The estimated difference between groups was 9.0 cm.

For Asian patients, waist circumference can be particularly useful because metabolic risk can be elevated even when BMI does not appear very high.

Blood Sugar Improved Too

Around 35% of participants had prediabetes at the beginning of the trial.

Among participants with prediabetes who received semaglutide:

• 30 of 36, or 83%, had returned to normoglycaemia by week 44

Among the placebo group:

• 6 of 16, or 38%, had returned to normoglycaemia

Average HbA1c also improved more in the semaglutide group than in the placebo group.

This does not prove that treatment will prevent diabetes in every patient, but it highlights the close relationship between weight management and metabolic health.

Blood Pressure and Cholesterol Also Changed

STEP 11 did not only measure body weight.

Researchers also looked at cardiometabolic markers.

Average systolic blood pressure decreased by:

• 11.1 mmHg with semaglutide
• 1.0 mmHg with placebo

Average diastolic blood pressure decreased by:

• 4.5 mmHg with semaglutide
• while the placebo group increased slightly by 0.8 mmHg

The study also reported improvements in:

• Total cholesterol
• LDL cholesterol
• Triglycerides
• C-reactive protein

These results show why medical weight management should not focus only on the number on the scale.

Who May Benefit From a Metabolic Health Assessment?

You do not need to wait until your BMI reaches 30 to discuss metabolic health with a doctor.

A medical assessment may be useful if you have:

• BMI around or above 25
• Increasing waist circumference
• Prediabetes
• High blood pressure
• High cholesterol
• Fatty liver concerns
• PCOS
• Family history of diabetes
• Repeated difficulty losing weight
• Weight-related sleep problems

For some people, lifestyle changes may be enough. Others may benefit from more structured support.

What a Doctor May Assess

A doctor-led weight-management assessment may include:

• Medical consultation
• BMI calculation
• Waist circumference
• Blood pressure
• Weight history
• Previous weight-loss attempts
• HbA1c or fasting glucose
• Lipid profile
• Liver function if needed
• Kidney function if needed
• Current medication review
• Weight-related conditions
• Treatment suitability
• Follow-up planning

This helps determine whether your BMI is simply a number or part of a wider metabolic risk pattern.

Safety and Side Effects in STEP 11

Side effects were reported more often in the semaglutide group than in the placebo group.

Adverse events occurred in:

• 89% of participants receiving semaglutide
• 78% receiving placebo

The most common were gastrointestinal symptoms such as:

• Nausea
• Diarrhoea
• Constipation

Most adverse events were mild to moderate.

Serious adverse events occurred in 13% of participants receiving semaglutide and 8% receiving placebo. Four people in the semaglutide group stopped treatment because of adverse events.

This is why prescription weight-management medication requires proper medical supervision.

Important Limitations of the Research

STEP 11 provides useful evidence, but it should be interpreted carefully.

The trial included only 150 participants.

Most participants were women, who made up 74% of the study population.

The treatment period lasted 44 weeks, so the trial does not answer every question about long-term treatment or weight maintenance after stopping.

The study was funded by Novo Nordisk, and several authors were employees or shareholders of the company. Other authors reported financial relationships with pharmaceutical companies.

These disclosures are important when interpreting research, even when the trial is randomised and peer-reviewed.

Why Doctor-Led Care Matters

A BMI of 25 does not automatically mean that someone needs medication.

A doctor should look at the bigger picture.

Two people with the same BMI can have very different:

• Waist measurements
• Blood sugar levels
• Blood pressure
• Cholesterol
• Body composition
• Family history
• Medical conditions

This is why treatment decisions should be based on metabolic health and individual risk rather than BMI alone.

Book a Weight Management Assessment in Bangkok

If your BMI is around 25 or above and you are concerned about weight, blood sugar, cholesterol, or metabolic health, a medical assessment can help clarify your risk.

MedConsult Clinic provides doctor-led weight management consultations in Bangkok, including BMI review, health history, metabolic screening, and blood testing where appropriate.

The first step is understanding your health profile before deciding whether lifestyle support, medication, or another approach is suitable.