BMI 25 in Thailand: What the STEP 11 Semaglutide Study Found

A BMI of 25 may not sound particularly high if you are used to international obesity cut-offs. In many Western guidelines, obesity is usually defined from a BMI of 30 kg/m². But for Asian populations, health risks can begin at lower BMI levels.

This matters in Thailand.

Asian populations tend to develop higher levels of body fat and visceral fat at the same BMI compared with many European populations. Because of this, lower BMI thresholds are used in several Asian countries. In the STEP 11 clinical trial, obesity was defined as BMI ≥25 kg/m² in line with local guidance in Thailand and South Korea.

The STEP 11 study, published in The Lancet Diabetes & Endocrinology in August 2025, investigated once-weekly semaglutide 2.4 mg alongside lifestyle intervention in Asian adults with obesity who did not have diabetes.

The findings are particularly relevant for patients in Thailand because the study included participants from both Thailand and South Korea and specifically examined treatment at the lower BMI threshold commonly used in Asian populations.

What Does BMI 25 Mean in Thailand?

BMI, or body mass index, compares weight with height and is commonly used as an initial screening tool for weight-related health risk.

In the STEP 11 paper, the authors note that local guidance in South Korea and Thailand uses:

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

This differs from the widely used international threshold of BMI ≥30 kg/m² for obesity.

The reason is not simply body size. Asian populations may develop metabolic complications at a lower BMI, partly because of differences in body composition and a tendency to accumulate more visceral fat around the organs.

BMI is still only one measurement. Waist circumference, blood pressure, blood sugar, cholesterol, medical history, and body composition can provide additional information about metabolic health.

Why BMI 25 in Thailand Matters

A person with a BMI of 25 may feel that their weight is only slightly above the “normal” range. But metabolic risk does not always match appearance.

Obesity is associated with conditions including:

• Type 2 diabetes
• High blood pressure
• Abnormal cholesterol
• Cardiovascular disease
• Fatty liver disease
• Sleep apnoea
• Joint problems
• Some cancers

The STEP 11 researchers highlighted that Asian populations may develop these complications at lower BMI levels than other populations. This is one reason population-specific BMI thresholds can matter when deciding who may benefit from earlier medical assessment.

What Was the STEP 11 Study?

STEP 11 was a 44-week, randomised, double-blind, placebo-controlled phase 3 trial conducted at 12 clinical sites in Thailand and South Korea.

A total of 150 Asian adults were randomly assigned in a 2:1 ratio:

• 101 received semaglutide 2.4 mg
• 49 received placebo

All participants also received lifestyle support involving a reduced-calorie diet and increased physical activity.

Participants had obesity defined as BMI ≥25 kg/m² and had previously made at least one unsuccessful attempt to lose weight.

Importantly, people with diabetes were excluded from the trial.

The average participant was 39 years old, with:

• Mean body weight: 83.8 kg
• Mean BMI: 31.3 kg/m²
• Mean waist circumference: 98.1 cm
• Mean HbA1c: 5.6%

Of the 150 participants, 65 were from Thailand and 85 were from South Korea.

What Did STEP 11 Find About Weight Loss?

The headline result was a significant difference in body weight between semaglutide and placebo at week 44.

Average body weight changed by:

• −16.0% with semaglutide
• −3.1% with placebo

The estimated difference between the groups was 13 percentage points.

The percentage of participants achieving different levels of weight reduction was also substantially higher in the semaglutide group.

At week 44:

• 96% achieved at least 5% weight loss
• 78% achieved at least 10%
• 53% achieved at least 15%
• 30% achieved at least 20%

These results came from a controlled clinical trial and should not be treated as a prediction of what every individual patient will achieve.

Weight-loss response varies according to starting weight, medical history, lifestyle, treatment tolerance, adherence, and individual biology.

What Happened to Waist Circumference?

Weight on the scale was not the only measure that changed.

Average waist circumference decreased by:

• 11.9 cm with semaglutide
• 3.0 cm with placebo

Waist circumference can be clinically useful because abdominal fat is closely related to metabolic risk.

The trial’s participants had a mean waist circumference of 98.1 cm at baseline, and most met the study’s criteria for abdominal obesity.

This reinforces why weight management should not focus only on kilograms. Waist circumference, blood pressure, blood sugar, and other metabolic markers also matter.

What Happened to Blood Sugar and Prediabetes?

STEP 11 also measured HbA1c, which reflects average blood sugar levels over the previous few months.

Over 44 weeks:

• Mean HbA1c decreased by 0.40 percentage points with semaglutide
• Mean HbA1c decreased by 0.03 percentage points with placebo

Among the 36 participants in the semaglutide group who had prediabetes at baseline, 30, or 83%, had returned to normoglycaemia by week 44.

In comparison, 6 of 16 participants with prediabetes in the placebo group returned to normoglycaemia.

This is an important finding, but it should not be interpreted as proof that treatment prevents diabetes in every patient. The trial was relatively short and specifically studied people without diabetes at baseline.

What Happened to Blood Pressure and Other Metabolic Markers?

The study also reported improvements in several cardiometabolic risk factors.

Average systolic blood pressure changed by:

• −11.1 mmHg with semaglutide
• −1.0 mmHg with placebo

Average diastolic blood pressure changed by:

• −4.5 mmHg with semaglutide
• +0.8 mmHg with placebo

The study also reported reductions in total cholesterol, LDL cholesterol, triglycerides, and C-reactive protein compared with placebo. HDL cholesterol was the exception.

These findings suggest that meaningful weight reduction may be accompanied by changes in wider metabolic health, not just body weight.

What About People With BMI Below 30?

One of the particularly relevant findings involved participants whose BMI was below 30 kg/m² at the beginning of the study.

There were 68 participants in this subgroup.

Among those receiving semaglutide, mean body-weight reduction over 44 weeks was 17.6%, compared with 4.4% in the placebo group.

This supports the study’s central question: whether weight-management treatment can have clinically meaningful effects in Asian people who meet the region’s lower obesity threshold even though their BMI would not necessarily be classified as obesity under some Western definitions.

However, BMI alone should not determine treatment. Medical assessment remains important.

What Side Effects Were Reported?

Side effects were common in both groups but occurred more frequently with semaglutide.

Adverse events were reported by:

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

The most frequently reported problems with semaglutide were gastrointestinal, including:

• Nausea
• Diarrhoea
• Constipation

Gastrointestinal adverse events occurred in 68% of the semaglutide group compared with 45% of the placebo group.

Most adverse events were described as mild to moderate. Serious adverse events occurred in 13% of participants receiving semaglutide and 8% receiving placebo.

Four participants receiving semaglutide stopped treatment because of adverse events. No cases of acute pancreatitis occurred during the study.

These results are one reason prescription weight-management medication should be used with medical assessment and follow-up.

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
• Current medications
• Blood sugar and HbA1c
• Lipid profile
• Liver and kidney function where appropriate
• Weight-related medical conditions
• Treatment suitability
• Side-effect risk
• Follow-up planning

BMI is useful as a starting point, but the decision to use medication should consider the patient’s overall health rather than one number alone.

What Are the Important Limitations of STEP 11?

The results are encouraging, but the study has limitations.

Only 150 participants were included, which is relatively small compared with some larger international obesity trials.

The study population was also predominantly female: 74% of participants were women.

Treatment lasted 44 weeks, so the study does not answer every question about long-term weight maintenance or what happens several years after treatment.

The study was also funded by Novo Nordisk, the manufacturer of semaglutide. Several authors were employees or shareholders of the company, while other authors reported relationships with pharmaceutical companies. The paper states that investigators verified the underlying data and retained responsibility for publication.

These disclosures do not invalidate the findings, but they are important when interpreting research responsibly.

Why Doctor-Led Care Matters

STEP 11 does not mean that everyone with a BMI of 25 should receive weight-loss medication.

Instead, the study highlights why Asian-specific metabolic risk deserves attention.

A patient with BMI 25 may have very different needs depending on:

• Waist circumference
• Blood pressure
• Prediabetes
• Cholesterol
• Fatty liver risk
• PCOS
• Family history
• Previous weight-loss attempts
• Overall body composition

For some patients, lifestyle changes may be enough. Others may benefit from structured medical weight management. The appropriate approach depends on individual assessment.

Book a Weight Management Consultation in Bangkok

For patients concerned about BMI 25 in Thailand, the first step does not have to be medication.

A medical consultation can help review BMI, waist circumference, blood sugar, blood pressure, cholesterol, lifestyle, and weight history before deciding whether further treatment is appropriate.

MedConsult Clinic provides doctor-led weight management consultations in Bangkok, including metabolic assessment and blood testing where clinically relevant.

The goal is to choose a treatment plan based on health risk and individual needs rather than BMI alone.