According to research, BMI alone isn't accurate in predicting metabolic health and may be particularly unreliable for athletes, the elderly and those who are pregnant. New studies suggest other methods may be more suitable, especially for those who belong to general populations.
What Is BMI?
BMI (Body Mass Index) uses your height and weight to work out a measurement to gauge if your weight is healthy. The BMI calculation is:
Weight in kilograms divided by height in metres squared
The current World Health Organisation (WHO) classifications outline:
- Severely underweight: BMI less than 16.5kg/m^2.
- Underweight: BMI under 18.5 kg/m^2.
- Normal weight: BMI greater than or equal to 18.5 to 24.9 kg/m^2.
- Overweight: BMI greater than or equal to 25 to 29.9 kg/m^2.
- Obesity: BMI greater than or equal to 30 kg/m^2.
- Obesity class I: BMI 30 to 34.9 kg/m^2.
The Research
Recent research, presented at the European Congress on Obesity and published in the journal Nutrients, has made headlines for its groundbreaking findings. The study suggests redefining obesity with a BMI threshold of 27 instead of the current standard of 30 set by the WHO.
Bodyweight Questions & Answers
Waist to Height Ratio Is a Better Indicator of Health than BMI, Says Research
Why Your Weight Isn't Always the Best Marker of Health
What Is a Healthy Body Fat Percentage?
The Methods
- The study included a total of 4800 participants: 1850 males and 2950 females.
- Body composition was measured using dual-energy x-ray absorptiometry (DEXA scan).
- The study employed something called 'receiver operating characteristic' (ROC) analysis to determine the most appropriate BMI cut off points for obesity based on the participant's body fat percentage.
The Results
The study identified significant disparities between the BMI cut off point and body fat percentage measurements. The current BMI cut off point demonstrated unreliable results across all age and sex groups, indicating a higher chance of being below the obesity cut off and a relatively lower chance of being above it.
This means that many individuals classified as non obese according to the WHO's BMI criteria were actually obese based on their body fat percentage.
The Conclusion
The study provides compelling evidence that the BMI cut off point of 30 is not optimal for detecting obesity in older adults. According to the study, adopting a lower cut off point of 27 could significantly improve obesity screening and health management.
Ideally, future research should focus on validating the cut off point in larger and more diverse populations, as well as investigating appropriate BMI cut off points for other categories such as underweight and overweight populations.
What Does This Mean for Us?
The study suggests that policymakers should consider adopting the new BMI cut off point of 27 for more accurate obesity screening in clinical settings. Should the cut off point be lowered by policymakers, as suggested by the research, those concerned about their health should be made aware of this.
However, at this point it hasn't been adjusted.
It's important to be aware of your BMI and current health status, but first consult your healthcare provider should you be worried about your measurements.
If you are unsure if your BMI is an accurate reading, as an easy alternative you can use waist-to-height or waist-to-hip ratios in conjunction with BMI as a more reliable measure. You can also take measurements such as body fat percentage in order to gain a more well rounded view of your health.
Kate is a fitness writer for Men’s Health UK where she contributes regular workouts, training tips and nutrition guides. She has a post graduate diploma in Sports Performance Nutrition and before joining Men’s Health she was a nutritionist, fitness writer and personal trainer with over 5k hours coaching on the gym floor. Kate has a keen interest in volunteering for animal shelters and when she isn’t lifting weights in her garden, she can be found walking her rescue dog.
