Body mass index, or BMI, is a method for calculating and estimating your body fat percentage based on your weight and height. To determine this calculation, you take your weight in kilograms and divide it by your height in metres squared. (BMI = weight (kg) / height (m)^2).
More researchers have concluded that BMI alone isn’t the most reliable predictor of metabolic health, particularly for athletes, pregnant women, and certain other populations. Researchers have also found that waistline measurements may be a better indicator of overall health than the body mass index (BMI). Waist circumference and waist-to-height ratio can be better predictors of these health risks.
When it comes to obesity, researchers suggest that the BMI cut-off point for obesity needs to be lowered. Let’s review the current research and classifications, as well as the new threshold suggestions.
What is considered a healthy or normal BMI?
Currently, the World Health Organisation (WHO) outlines the following BMI classifications:
| Classification | BMI |
| Severely underweight | Below 16.5kg/m^2 |
| Underweight | Below 18.5 kg/m^2 |
| Normal weight | Greater than or equal to 18.5 to 24.9 kg/m^2 |
| Overweight | Greater than or equal to 25 to 29.9 kg/m^2 |
| Obesity | Greater than or equal to 30 kg/m^2 |
| Obesity class I | Between 30 to 34.9 kg/m^2 |
The new suggested cut-off point for obesity
Researchers in a new study published in the journal Nutrients concluded that the current BMI thresholds might not be the most suitable for identifying obesity. The study involved 4800 men and women, and the researchers assessed body composition using DEXA scans. The study involved a receiver operating characteristic (ROC) analysis to help the researchers assess the most suitable BMI threshold for obesity according to the individual’s body fat percentage.
The new suggested threshold
The researchers suggested that the WHO standard guidelines, with a BMI threshold for obesity set at 30, are too high and should instead be lowered to 27. This means that some of those individuals who would now be considered overweight according to their BMI would be considered obese instead.
The study authors pointed out that the current BMI categories are unreliable across all ages and sexes, showing a potentially higher likelihood of being under the obesity point and a lower likelihood of being above it. In other words, many participants who were placed in the non-obese category based on the current BMI criteria were obese according to their body fat percentage. The current guidelines are also the same for both men and women.
Concluding thoughts
More medical professionals and fitness enthusiasts are moving away from relying solely on BMI as an indicator of metabolic health risks and obesity. Instead, they’re also using other markers and measurements, such as waist circumference and waist-to-height ratio. This study shows that the BMI set point of 30 isn’t the most effective way to identify obesity, especially in older adults. A lower set point of 27 could be a superior choice.
