Mental Health Self-Check (PHQ-9 Style)

BMI (Body Mass Index) is a screening tool that uses height and weight to classify body composition into standard categories. While originally designed as a population-level metric, research has also examined its relationship with psychological well-being, self-esteem, and mental health outcomes.

BMI formula: BMI = Weight (kg) / Height (m)² BMI (Imperial) = (Weight (lbs) × 703) / Height (inches)²

Standard BMI categories (WHO):

Worked example: A person 175 cm (1.75 m) tall, weighing 82 kg:

• BMI = 82 / (1.75)² = 82 / 3.0625 = 26.8 → Overweight

BMI and mental health — research findings:

• Both underweight (BMI < 18.5) and severe obesity (BMI ≥ 35) are associated with higher rates of depression and anxiety in large population studies
• The relationship is bidirectional: mental health conditions can cause weight changes, and weight changes affect mental health
• Body image dissatisfaction — regardless of actual BMI — is a stronger predictor of depression than BMI itself
• Social stigma around weight affects mental well-being independently of physical health

Critical limitations of BMI:

• Does not measure body fat percentage directly
• Does not account for muscle mass (athletes often score “overweight”)
• Does not reflect fat distribution (visceral vs. subcutaneous fat)
• Less accurate for elderly populations, children, and some ethnic groups

Better complementary measures: Waist-to-height ratio (WHtR < 0.5 is healthy), waist circumference, and DEXA body composition scans provide a more complete picture.