Body Mass Index (BMI)
Body Mass Index (BMI)
Body Mass Index (BMI) is a measure of body weight relative to height, used to categorise weight status and assess potential health risks.
Body Mass Index (BMI) is a measure of body weight relative to height, used to categorise weight status and assess potential health risks.
Body Mass Index (BMI)
Normal range
Normal range
18.5-25 kg/m²
18.5-25 kg/m²
Normal range
18.5-25 kg/m²
18.5-25 kg/m²
Normal range
Body Mass Index (BMI)
Body Mass Index (BMI)
Body Mass Index (BMI) is a measure of body weight relative to height, used to categorise weight status and assess potential health risks.
Body Mass Index (BMI)
Normal range
18.5-25 kg/m²
Normal range
18.5-25 kg/m²
18.5-25 kg/m²
Normal range
Body Mass Index (BMI)
Body Mass Index (BMI)
Body Mass Index (BMI) is a measure of body weight relative to height, used to categorise weight status and assess potential health risks.
Body Mass Index (BMI)
Normal range
18.5-25 kg/m²
Normal range
18.5-25 kg/m²
18.5-25 kg/m²
Normal range
Body Mass Index (BMI)
Dr. Yiannis Balanos
MBBS MRCGP
Your Weight-to-Height Health Indicator
Your Weight-to-Height Health Indicator
Body Mass Index (BMI) is a screening tool that uses your weight and height to estimate whether you're in a healthy weight range. Calculated as weight in kilograms divided by height in metres squared, BMI provides a quick assessment of potential weight-related health risks. Whilst BMI has limitations and doesn't measure body composition directly, it remains a valuable starting point for health discussions and health monitoring.
Body Mass Index (BMI) is a screening tool that uses your weight and height to estimate whether you're in a healthy weight range. Calculated as weight in kilograms divided by height in metres squared, BMI provides a quick assessment of potential weight-related health risks. Whilst BMI has limitations and doesn't measure body composition directly, it remains a valuable starting point for health discussions and health monitoring.
When BMI Categories Affect Your Health
When BMI Categories Affect Your Health
When BMI Categories Affect Your Health
Discover how underweight, normal, overweight, and obese BMI ranges correlate with different health risks and outcomes.
Read more
What Influences Your BMI
What Influences Your BMI
What Influences Your BMI
Learn about the factors that determine your BMI and understand its strengths and limitations as a health assessment tool.
Read more
Improving Your BMI When Needed
Improving Your BMI When Needed
Improving Your BMI When Needed
Understand evidence-based approaches to achieving a healthier BMI through sustainable lifestyle changes.
Read more
Understanding Your BMI Results
Understanding Your BMI Results
Understanding Your BMI Results
Find out what your BMI category means, when it might be misleading, and how to interpret it alongside other health markers.
Read more
When BMI Categories Affect Your Health
Underweight (BMI <18.5): A BMI below 18.5 may indicate insufficient body weight for optimal health. Significantly underweight individuals face increased risks of weakened immune systems, slower, osteoporosis, and fertility problems. This category, if significantly under a BMI of 18, may reflect inadequate nutrition or underlying medical conditions.
Normal Weight (BMI 18.5-25): This range is associated with the lowest risk of weight-related health problems for most people. However, even within this range, body composition, fitness level, and fat distribution can influence individual health profiles.
Overweight (BMI 25-29.9): Being overweight increases risks of developing metabolic syndrome and high blood pressure, for example. However, some individuals in this category, particularly those who are physically active with good muscle mass, may have lower health risks than their BMI suggests, so a case-by-case assessment should be considered.
Obese (BMI 30-40) and Severely Obese (BMI >40): Obesity significantly increases risks of serious health conditions including heart disease, stroke, type 2 diabetes, certain cancers, and sleep apnoea. Severe obesity further amplifies these risks and may also impact mobility, joint health, and quality of life. However, even modest weight reduction can provide substantial health benefits.
When BMI Categories Affect Your Health
Underweight (BMI <18.5): A BMI below 18.5 may indicate insufficient body weight for optimal health. Significantly underweight individuals face increased risks of weakened immune systems, slower, osteoporosis, and fertility problems. This category, if significantly under a BMI of 18, may reflect inadequate nutrition or underlying medical conditions.
Normal Weight (BMI 18.5-25): This range is associated with the lowest risk of weight-related health problems for most people. However, even within this range, body composition, fitness level, and fat distribution can influence individual health profiles.
Overweight (BMI 25-29.9): Being overweight increases risks of developing metabolic syndrome and high blood pressure, for example. However, some individuals in this category, particularly those who are physically active with good muscle mass, may have lower health risks than their BMI suggests, so a case-by-case assessment should be considered.
Obese (BMI 30-40) and Severely Obese (BMI >40): Obesity significantly increases risks of serious health conditions including heart disease, stroke, type 2 diabetes, certain cancers, and sleep apnoea. Severe obesity further amplifies these risks and may also impact mobility, joint health, and quality of life. However, even modest weight reduction can provide substantial health benefits.
When BMI Categories Affect Your Health
Underweight (BMI <18.5): A BMI below 18.5 may indicate insufficient body weight for optimal health. Significantly underweight individuals face increased risks of weakened immune systems, slower, osteoporosis, and fertility problems. This category, if significantly under a BMI of 18, may reflect inadequate nutrition or underlying medical conditions.
Normal Weight (BMI 18.5-25): This range is associated with the lowest risk of weight-related health problems for most people. However, even within this range, body composition, fitness level, and fat distribution can influence individual health profiles.
Overweight (BMI 25-29.9): Being overweight increases risks of developing metabolic syndrome and high blood pressure, for example. However, some individuals in this category, particularly those who are physically active with good muscle mass, may have lower health risks than their BMI suggests, so a case-by-case assessment should be considered.
Obese (BMI 30-40) and Severely Obese (BMI >40): Obesity significantly increases risks of serious health conditions including heart disease, stroke, type 2 diabetes, certain cancers, and sleep apnoea. Severe obesity further amplifies these risks and may also impact mobility, joint health, and quality of life. However, even modest weight reduction can provide substantial health benefits.
What Influences Your BMI
Your BMI reflects the relationship between your weight and height, but numerous factors influence this calculation. Muscle mass significantly affects BMI—athletic individuals may have "overweight" BMIs despite excellent health due to higher muscle composition, as muscle weighs more than fat.
Age can influence BMI interpretation, as older adults may benefit from slightly higher BMIs due to age-related muscle loss and the protective effects of some additional weight for bone health.
BMI doesn't distinguish between muscle, fat, bone, and organs, making it less accurate for very muscular individuals, pregnant women, or those with significant fluid retention. It also doesn't account for fat distribution, which significantly influences health risks.
What Influences Your BMI
Your BMI reflects the relationship between your weight and height, but numerous factors influence this calculation. Muscle mass significantly affects BMI—athletic individuals may have "overweight" BMIs despite excellent health due to higher muscle composition, as muscle weighs more than fat.
Age can influence BMI interpretation, as older adults may benefit from slightly higher BMIs due to age-related muscle loss and the protective effects of some additional weight for bone health.
BMI doesn't distinguish between muscle, fat, bone, and organs, making it less accurate for very muscular individuals, pregnant women, or those with significant fluid retention. It also doesn't account for fat distribution, which significantly influences health risks.
What Influences Your BMI
Your BMI reflects the relationship between your weight and height, but numerous factors influence this calculation. Muscle mass significantly affects BMI—athletic individuals may have "overweight" BMIs despite excellent health due to higher muscle composition, as muscle weighs more than fat.
Age can influence BMI interpretation, as older adults may benefit from slightly higher BMIs due to age-related muscle loss and the protective effects of some additional weight for bone health.
BMI doesn't distinguish between muscle, fat, bone, and organs, making it less accurate for very muscular individuals, pregnant women, or those with significant fluid retention. It also doesn't account for fat distribution, which significantly influences health risks.
Improving Your BMI When Needed
For those with BMIs outside the healthy range, focus on sustainable lifestyle changes rather than rapid weight changes. Create modest calorie deficits through improved diet quality and increased physical activity. Emphasise whole foods, appropriate portion sizes, and regular meal timing.
Include both cardiovascular exercise and strength training to support healthy body composition changes. Building muscle mass can improve metabolism and body composition even when BMI changes slowly.
Address underlying factors that may contribute to unhealthy BMI, including sleep quality and stress. Work with healthcare providers to develop safe, effective strategies tailored to your individual circumstances and health status.
Improving Your BMI When Needed
For those with BMIs outside the healthy range, focus on sustainable lifestyle changes rather than rapid weight changes. Create modest calorie deficits through improved diet quality and increased physical activity. Emphasise whole foods, appropriate portion sizes, and regular meal timing.
Include both cardiovascular exercise and strength training to support healthy body composition changes. Building muscle mass can improve metabolism and body composition even when BMI changes slowly.
Address underlying factors that may contribute to unhealthy BMI, including sleep quality and stress. Work with healthcare providers to develop safe, effective strategies tailored to your individual circumstances and health status.
Improving Your BMI When Needed
For those with BMIs outside the healthy range, focus on sustainable lifestyle changes rather than rapid weight changes. Create modest calorie deficits through improved diet quality and increased physical activity. Emphasise whole foods, appropriate portion sizes, and regular meal timing.
Include both cardiovascular exercise and strength training to support healthy body composition changes. Building muscle mass can improve metabolism and body composition even when BMI changes slowly.
Address underlying factors that may contribute to unhealthy BMI, including sleep quality and stress. Work with healthcare providers to develop safe, effective strategies tailored to your individual circumstances and health status.
Understanding Your BMI Results
BMI is expressed as kg over metres squared (kg/m²).
BMI Categories:
Underweight: <18.5
Normal: 18.5-24.9
Overweight: 25-29.9
Obese: 30-40
Severe obesity: >40
Remember that BMI is a screening tool, not a diagnostic test. It provides useful population-level health information but may not accurately reflect individual health status. Consider BMI alongside other health indicators including waist circumference, fitness level, blood pressure, and metabolic markers.
For individuals with high muscle mass or specific medical conditions, BMI may be less accurate. Healthcare providers may use additional assessments like body composition analysis or waist-to-hip ratios for more complete evaluation.
Understanding Your BMI Results
BMI is expressed as kg over metres squared (kg/m²).
BMI Categories:
Underweight: <18.5
Normal: 18.5-24.9
Overweight: 25-29.9
Obese: 30-40
Severe obesity: >40
Remember that BMI is a screening tool, not a diagnostic test. It provides useful population-level health information but may not accurately reflect individual health status. Consider BMI alongside other health indicators including waist circumference, fitness level, blood pressure, and metabolic markers.
For individuals with high muscle mass or specific medical conditions, BMI may be less accurate. Healthcare providers may use additional assessments like body composition analysis or waist-to-hip ratios for more complete evaluation.
Understanding Your BMI Results
BMI is expressed as kg over metres squared (kg/m²).
BMI Categories:
Underweight: <18.5
Normal: 18.5-24.9
Overweight: 25-29.9
Obese: 30-40
Severe obesity: >40
Remember that BMI is a screening tool, not a diagnostic test. It provides useful population-level health information but may not accurately reflect individual health status. Consider BMI alongside other health indicators including waist circumference, fitness level, blood pressure, and metabolic markers.
For individuals with high muscle mass or specific medical conditions, BMI may be less accurate. Healthcare providers may use additional assessments like body composition analysis or waist-to-hip ratios for more complete evaluation.
The Takeaway
BMI serves as a useful initial screening tool for weight-related health risks, providing a standardised way to assess whether your weight falls within generally healthy ranges. However, BMI is just one variable of your health equation and should be considered alongside other factors including body composition, fitness level, and overall health.
Focus on achieving a BMI within the healthy range through sustainable lifestyle changes that emphasise overall health rather than just weight loss. Remember that BMI has limitations—it doesn't account for muscle mass, fat distribution, or individual variations that influence overall health.
The Takeaway
BMI serves as a useful initial screening tool for weight-related health risks, providing a standardised way to assess whether your weight falls within generally healthy ranges. However, BMI is just one variable of your health equation and should be considered alongside other factors including body composition, fitness level, and overall health.
Focus on achieving a BMI within the healthy range through sustainable lifestyle changes that emphasise overall health rather than just weight loss. Remember that BMI has limitations—it doesn't account for muscle mass, fat distribution, or individual variations that influence overall health.
The Takeaway
BMI serves as a useful initial screening tool for weight-related health risks, providing a standardised way to assess whether your weight falls within generally healthy ranges. However, BMI is just one variable of your health equation and should be considered alongside other factors including body composition, fitness level, and overall health.
Focus on achieving a BMI within the healthy range through sustainable lifestyle changes that emphasise overall health rather than just weight loss. Remember that BMI has limitations—it doesn't account for muscle mass, fat distribution, or individual variations that influence overall health.
References
World Health Organization. (2024). Body mass index - BMI. WHO Global Health Observatory data repository.
Keys, A., Fidanza, F., Karvonen, M.J., Kimura, N., & Taylor, H.L. (1972). Indices of relative weight and obesity. Journal of Chronic Diseases, 25(6-7), 329-343.
Flegal, K.M., Kit, B.K., Orpana, H., & Graubard, B.I. (2013). Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis. JAMA, 309(1), 71-82.
Nuttall, F.Q. (2015). Body mass index: obesity, BMI, and health: a critical review. Nutrition Today, 50(3), 117-128.
References
World Health Organization. (2024). Body mass index - BMI. WHO Global Health Observatory data repository.
Keys, A., Fidanza, F., Karvonen, M.J., Kimura, N., & Taylor, H.L. (1972). Indices of relative weight and obesity. Journal of Chronic Diseases, 25(6-7), 329-343.
Flegal, K.M., Kit, B.K., Orpana, H., & Graubard, B.I. (2013). Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis. JAMA, 309(1), 71-82.
Nuttall, F.Q. (2015). Body mass index: obesity, BMI, and health: a critical review. Nutrition Today, 50(3), 117-128.
References
World Health Organization. (2024). Body mass index - BMI. WHO Global Health Observatory data repository.
Keys, A., Fidanza, F., Karvonen, M.J., Kimura, N., & Taylor, H.L. (1972). Indices of relative weight and obesity. Journal of Chronic Diseases, 25(6-7), 329-343.
Flegal, K.M., Kit, B.K., Orpana, H., & Graubard, B.I. (2013). Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis. JAMA, 309(1), 71-82.
Nuttall, F.Q. (2015). Body mass index: obesity, BMI, and health: a critical review. Nutrition Today, 50(3), 117-128.
Research articles
Research articles
Control your preventive health with Emerald
Subscribe to our newsletter
© 2025 Emerald Labs Ltd
Subscribe to our newsletter
© 2025 Emerald Labs Ltd
Subscribe to our newsletter
© 2025 Emerald Labs Ltd
Subscribe to our newsletter
© 2025 Emerald Labs Ltd
Subscribe to our newsletter
© 2025 Emerald Labs Ltd