Everyone knows that keeping body fit and lean is good for health.
A high level of body fat or obesity can lead to cardiovascular diseases or metabolic disorders such as diabetes and hypertension.
However, too little body fat can be also unhealthy, as it is essential for regulating glucose, cholesterol, energy storage and release, and reproductive hormone metabolism.
Then, how can you determine whether your body is fit and lean?
There are two key mearsurements, Body Mass Index(BMI) and Body Fat Percentage.
Body Mass Index(BMI)
What is BMI?
BMI is a calculation that uses your height and weight to estimate body fat.
It is widely used as a simple way to classify individuals as underweight, normal weight, overweight, or obese.
The formula is:
Why is BMI used as a measure of obesity?
BMI is commonly used because it provides a quick and easy estimate of body fat.
The World Health Organization (WHO) has adopted BMI as a global standard for assessing overweight and obesity.
According to the WHO’s classification:
| Category | BMI Range(kg/m²) |
| Underweight | Below 18.5 |
| Normal | 18.5~24.9 |
| Overweight | 25~29.9 |
| Obesity Class I | 30~34.9 |
| Obesity Class II | 35~40 |
| Obesity Class III | Above 40 |
(Source: World Health Organization)
Limitations of BMI
Although BMI is useful, it doesn’t account for muscle mass or fat distribution.
Let’s take an example of an athlete:
he weighs 88 kg and have a BMI of 27.8, which classifies them as overweight.
However, in reality, they have a body fat percentage of only 7.1%, indicating they have a very healthy and muscular body.
That’s why it’s important to consider Body Fat Percentage alongside BMI.
Body Fat Percentage
Why body fat percentage is important?
Body fat percentage measures the proportion of your weight that comes from fat.
It is a more accurate measure of fitness and health than BMI because it distinguishes between fat and lean mass.
Body fat percentage gives a clearer picture of your body composition.
The American Council on Exercise (ACE) provides a helpful guideline for interpreting body fat percentage:
| Category | Men (Body Fat %) |
Women (Body Fat %) |
| Essential Fat | 2~5% | 10~13% |
| Athletes | 6~13% | 14~20% |
| Fitness | 14~17% | 21~24% |
| Acceptable | 18~24% | 25~31% |
| Obese | Above 25% | Above 32% |
Unlike BMI, which is an overly simplistic measure that often falls short in determining fatness in certain individuals, body fat percentage provides a direct measurement of actual body fat.
This is crucial for assessing risks related to cardiovascular diseases and metabolic conditions like diabetes.
A study(Percent body fat is a better predictor of cardiovascular risk factors than body mass index) by Zeng et al. (2009) found that body fat percentage (PBF) is a better predictor of cardiovascular risk factors than BMI.
In this study, abnormal BMI but normal PBF group did not show a significant increase in risk of cardiovascular health compared to normal BMI and PBF group.
However, the group with abnormal PBF but normal BMI group shows 1.88 times higher risk.
BMI is too general; therefore, combining it with body fat percentage provides a more useful health metric.
How to measure body fat percentage?
There are several methods to measure body fat percentage:
- DEXA Scan (Dual-Energy X-ray Absorptiometry): A highly accurate method that measures bone density and body fat distribution.
- Bioelectrical Impedence Tools (including InBody): A commonly used tool in gyms and clinics that uses bioelectrical impedance to estimate body composition.
- Hydrostatic Weighing: An older but reliable technique where the person is submerged in water to calculate body density and fat.
- Skinfold Calipers: A simple and less expensive method that measures the thickness of skinfolds at various points on the body.
- CT or MRI Scans: These imaging techniques can precisely assess fat distribution but are costly.
- Visual Estimation: The simplest method is to visually estimate body fat, but this approach is subjective and difficult to quantify.
AI-based body fat percentage visual estimation?
SENTIF, researching a simple but objective method for visual estimation of body fat, developed an AI-based image model for predicting body fat percentage.
Using a paired dataset of over 5,000 upper body images and body composition analysis results (from DEXA scans or bioelectrical impedance), the model has been showing a high level of accuracy, with a mean absolute error of only 1.5%p compared to actual body composition results in internally validation test.
You can access the service for free through the following link: (SENTIF-FIT Scanner)
References
https://www.who.int/europe/news-room/fact-sheets/item/a-healthy-lifestyle---who-recommendations
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3854278/
https://www.acefitness.org/fitness-certificatio