From the Guidelines
Body Mass Index (BMI) should be calculated and interpreted using the World Health Organization (WHO) standard weight status categories, which define underweight as a BMI of < 18.5, normal weight as 18.5 to 24.9, overweight as 25.0 to 29.9, and obese as >= 30, as stated in the 2020 update of the KDOQI clinical practice guideline for nutrition in CKD 1. To calculate BMI, divide your weight in kilograms by your height in meters squared (BMI = kg/m²). Key points to consider when using BMI include:
- BMI is not an ideal marker of obesity because it cannot differentiate between higher weights due to increased adiposity versus muscularity and it cannot identify visceral adiposity, which has negative metabolic effects 1.
- Population-specific BMI cutoffs to define weight status may be lower for Asian populations 1.
- Height should be measured periodically to ensure the accuracy of BMI 1.
- BMI should be considered alongside other measurements like waist circumference, blood pressure, blood sugar, and cholesterol levels for accurate health assessment.
- Regular monitoring of BMI can help track weight changes over time and guide health decisions, but it should be interpreted in consultation with healthcare providers for personalized recommendations.
From the Research
Definition and Measurement of Body Mass Index
- Body Mass Index (BMI) is defined as a metric used to categorize individuals into different weight categories, with a BMI of 30 kg/m2 or higher indicating obesity 2.
- BMI is calculated by dividing an individual's weight in kilograms by their height in meters squared, and is widely used as a risk factor for the development of various health issues 3.
- However, BMI has been criticized for being a poor indicator of percent body fat, and does not capture information on the mass of fat in different body sites 3.
Trends in Body Mass Index
- Worldwide trends in BMI have shown an increase in the prevalence of obesity, with a 27.5% increase in adults and 47.1% increase in children over the last three decades 2.
- A study of 2416 population-based measurement studies found that the global age-standardised prevalence of obesity increased from 0.7% in 1975 to 5.6% in 2016 in girls, and from 0.9% in 1975 to 7.8% in 2016 in boys 4.
- Regional trends in BMI have varied, with some countries experiencing a plateau in BMI trends, while others have seen an acceleration in the rise of BMI 4.
Limitations and Alternatives to Body Mass Index
- BMI has been shown to be a poor surrogate marker of actual adiposity, and alternative methods such as percent body fat (%BF) have been proposed as a more accurate measure of obesity 5.
- A study found that %BF thresholds based on key obesity-related comorbidities, such as metabolic syndrome, could be used to define overweight and obesity, with thresholds of 25%BF and 30%BF for men, and 36%BF and 42%BF for women 5.
- Other studies have explored the use of alternative measures, such as waist circumference and waist-to-hip ratio, to assess obesity and related health risks 6.