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Body Mass Index

Body Mass Index (BMI) is a common metric used to assess whether a person's weight is healthy relative to their height.

AI-compiled · not individually reviewed · Published

Typical adult reference range: 18.5 – 24.9 kg/m²
Ranges differ between laboratories, assays, sex and age. The range printed on your own report takes precedence over this one.

What is BMI?

Body Mass Index (BMI) is a numerical value derived from an individual's weight and height. It is calculated by dividing a person's weight in kilograms by the square of their height in meters. BMI is widely used as a screening tool to categorize individuals into weight status groups such as underweight, normal weight, overweight, and obesity.

How is BMI calculated?

Weight (kg) / [Height (m)]²

Inputs: WEIGHT · HEIGHT

Weight is measured in kilograms and height in meters.

What does BMI do in the body?

BMI is primarily used as an indicator of body fatness for most people and can predict health risks associated with different weight categories. However, it does not directly measure body fat or distinguish between fat and muscle mass. For example, athletes with high muscle mass might have a high BMI without having excessive body fat.

What does a high BMI mean?

A high BMI typically suggests that a person has excess body weight for their height, often indicating overweight or obesity. This is associated with an increased risk of various health conditions, including heart disease, type 2 diabetes, high blood pressure, certain cancers, and sleep apnea.

Common causes:

  • Excessive caloric intake
  • Lack of physical activity
  • Genetic predisposition
  • Certain medical conditions (e.g., hypothyroidism, Cushing's syndrome)
  • Medication side effects

What does a low BMI mean?

A low BMI suggests that a person's weight is lower than what is generally considered healthy for their height, indicating underweight. Being underweight can also be associated with health risks such as nutritional deficiencies, weakened immune function, osteoporosis, and fertility issues.

Common causes:

  • Insufficient caloric intake or malnutrition
  • High metabolism
  • Intense physical activity without adequate caloric intake
  • Eating disorders (e.g., anorexia nervosa)
  • Chronic diseases (e.g., hyperthyroidism, inflammatory bowel disease, cancer)

What moves BMI apart from disease?

Muscle Mass raises it
Individuals with high muscle mass (e.g., bodybuilders) may have a high BMI without excess body fat.
Age either direction
BMI interpretations can vary by age, especially for children and older adults. Muscle mass tends to decrease with age, affecting BMI interpretation.
Sex either direction
Men and women naturally have different body compositions, affecting how BMI correlates with body fat percentage.
Ethnicity either direction
Different ethnic groups may have different associations between BMI, body fat percentage, and health risks, necessitating specific guidelines for some populations.

Which lifestyle factors affect BMI?

Balanced Diet strong evidence
Adopting a balanced diet rich in fruits, vegetables, lean proteins, and whole grains, while limiting processed foods, sugary drinks, and unhealthy fats, can help maintain a healthy weight and BMI.
Regular Physical Activity strong evidence
Engaging in regular physical activity, including aerobic exercise and strength training, helps manage weight, build muscle, and improve overall body composition, thereby influencing BMI.
Adequate Sleep moderate evidence
Sufficient and quality sleep is important for hormonal regulation that affects appetite and metabolism, indirectly influencing weight management and BMI.

How should you prepare for a BMI test?

  • Ensure accurate and consistent measurement of height and weight, preferably using calibrated equipment.
  • Measure weight at the same time of day (e.g., in the morning before breakfast) and in similar clothing to minimize variability.

References

  1. World Health Organization. Body mass index – BMI. 2023. — https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight
  2. Centers for Disease Control and Prevention. About Adult BMI. 2023. — https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html
  3. Nuttall FQ. Body Mass Index (BMI): A Critical Review. Nutr Today. 2015 May;50(3):117-135. — https://doi.org/10.1097/NT.0000000000000092

Track your own BMI over time in Orviva →

Compiled automatically by AI from published medical literature, without line-by-line human checking, and it may contain errors or out-of-date information. For general health education only — it does not replace diagnosis or treatment advice from a doctor. Check the references and talk to a clinician before acting on anything involving medication, supplements or treatment.