Body Mass Index vs. Fat Mass Index

Dr. Lowell Greib MSc ND CISSN

Body Mass Index (BMI) and Fat Mass Index (FMI) are two commonly used anthropometric measures to assess an individual’s body composition and health. While BMI has been widely used for decades, there is growing evidence suggesting that FMI may be a more preferable and accurate indicator of health, particularly in assessing obesity-related risks. FMI is part of the routine process of body composition analysis at The SportLab. The following summary outlines key reasons why FMI is considered preferable to BMI.

  • FMI Reflects Body Composition:
    • BMI is a simple calculation based on weight and height (BMI = weight in kilograms / (height in meters)²), making it easy to compute. However, it does not consider the distribution of fat and lean mass in the body.
    • FMI takes into account the proportion of fat mass relative to an individual’s height (FMI = fat mass in kilograms / (height in meters)²). FMI provides a more accurate representation of an individual’s body composition.
  • FMI Accounts for Variability:
    • BMI does not account for variations in muscle mass, bone density, or fat distribution among individuals, leading to potential misclassification.
    • FMI adjusts for these factors by directly quantifying fat mass, offering a more precise assessment of adiposity.
  • FMI Predicts Health Outcomes:
    • Numerous studies have indicated that FMI is a better predictor of obesity-related health outcomes, such as metabolic syndrome, cardiovascular disease, and type 2 diabetes, compared to BMI.
    • FMI provides a clearer picture of the health risks associated with excess fat mass.
  • FMI in Clinical Practice:
    • FMI has been suggested as a more appropriate tool for clinicians when assessing individual health risks and planning interventions, especially in cases where BMI may not provide an accurate assessment.
    • FMI may enhance the precision of obesity diagnosis and management.

While BMI remains a valuable tool for initial screening and epidemiological studies due to its simplicity, FMI offers a more comprehensive and accurate assessment of body composition and health risks associated with excess fat mass. Our clinicians recognize the advantages of using FMI in conjunction with BMI or as a standalone measurement to improve the precision of body composition assessment and its implications for health outcomes.

Should you have questions about body composition testing or would like testing completed, feel free to contact one of our clinical team!

  • Müller et al. (2010). Beyond BMI: Conceptual Issues Related to Overweight and Obese Patients. Obesity, 18(11), 2133-2137.
  • Kyle et al. (2003). Fat-free and fat mass percentiles in 5225 healthy subjects aged 15 to 98 years. Nutrition & Metabolism, 18(11), 1355-1362.
  • Lee et al. (2008). Discrimination of metabolic syndrome using distinct thresholds of insulin sensitivity. Diabetes Care, 31(7), 1444-1446.
  • López-Alarcón et al. (2014). Fat mass index performs best in monitoring management of obesity in prepubertal children. Journal of the American Dietetic Association, 114(9), 1354-1358.

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