Body Mass Index (BMI) is a screening measurement widely used in clinical practice that the World Health Organization uses as the basis for obesity classification. In this article, we explain how it is calculated, what it means, and its threshold values for medical interventions such as a gastric balloon.
What Is BMI and How Is It Calculated?
Formula:
BMI = Weight (kg) ÷ Height² (m²)
Example: For someone weighing 75 kg with a height of 1.68 m:
BMI = 75 ÷ (1.68 × 1.68) = 75 ÷ 2.82 = 26.6 kg/m²
WHO Obesity Classification
| BMI Range | Classification |
|---|---|
| < 18.5 | Underweight |
| 18.5 – 24.9 | Normal |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Class I Obesity |
| 35.0 – 39.9 | Class II Obesity |
| ≥ 40.0 | Class III Obesity (Morbid Obesity) |
Medical Intervention Thresholds
The BMI value is an important guide in determining which treatment options will be considered:
| BMI | Options |
|---|---|
| 25–27 | Lifestyle change, nutrition counseling |
| ≥ 27 | The Allurion swallowable gastric balloon may be considered |
| ≥ 30 | GLP-1 drug therapy may be added |
| ≥ 35 + comorbidity | Bariatric surgery on the agenda |
| ≥ 40 | Bariatric surgery a strong indication |
Threshold values are guidance only. The final decision rests with your physician.
BMI Value for Allurion
According to general application guidelines:
- Lower limit: BMI ≥ 27 kg/m²
- Upper limit: Generally 40 kg/m² — above this, a bariatric surgery bridge may be discussed
- Suitable range: The BMI 27–35 range is the group for which the swallowable gastric balloon is typically recommended in clinical evaluations; individual results may vary.
These values form a general framework. Your physician will make an assessment based on your medical history and individual risk profile.
The Limitations of BMI
While BMI is practical and widely used, it has some limitations:
It does not distinguish muscle mass: Someone who exercises intensively may fall into the "obese" category even though their body fat is actually low.
It does not show fat distribution: Fat accumulation in the abdominal region (visceral fat) carries cardiometabolic risk independent of total fat. Waist circumference measurement provides additional information.
It must be interpreted according to age and sex: The same BMI value may carry a different risk meaning at age 25 versus age 60.
Ethnic differences: Some guidelines recommend lower BMI thresholds for individuals of Asian descent.
Waist Circumference: A Complementary Measurement
According to WHO recommendations, the risk limits are:
| Sex | Caution | High Risk |
|---|---|---|
| Female | ≥ 80 cm | ≥ 88 cm |
| Male | ≥ 94 cm | ≥ 102 cm |
Waist circumference reflects visceral (intra-abdominal) fat accumulation and more directly indicates cardiovascular risk.
Calculate Your BMI
After learning your BMI value, you can discuss which options are suitable for you in a consultation with a specialist physician.
Frequently Asked Questions
My BMI is 26, can a gastric balloon be applied? The general threshold is BMI ≥ 27. A specialist evaluation is required for a value of 26 — individual factors (waist circumference, metabolic status, past interventions) influence the decision-making process.
My BMI is 42, gastric balloon or surgery? For a BMI of 42, bariatric surgery is the primary option. That said, the balloon may be considered as a "bridge therapy" to reduce surgical risk. Make this decision with your bariatric surgeon.
Which category will my BMI drop to after losing weight? In clinical studies, a mean of ~15% (14.9%) total body weight loss (TBWL) has been reported (PMID 32279182); with this average, someone with a starting BMI of 35 could drop to approximately BMI 30. Individual results may vary.
Further reading:
- BMI Calculator →
- Current Options in Obesity Treatment 2026 →
- Who Is the Gastric Balloon Applied To? →
- Obesity Rates in Türkiye →
- Find a Specialist →
This content is for general informational purposes based on WHO classification criteria. Consult your physician for a personal evaluation.
An Authorized Clinic in a City Near You
You can have the Allurion Program applied at more than 60 authorized clinics across Türkiye. For clinics in major cities:
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