Body mass index (BMI) is one of the most common methods to assess one's body composition and decide if a person is underweight, normal, overweight or obese. The formula to calculate BMI is simple and you can see it in most of the gyms around the world. You just need to take your weight in kilograms and divide it by the square of your height in meters.
This method is all well and good. However, it just looks at weight and ignores things like muscle, sex, age, bone mass, organs, and skin.
The BMI still has some limitations when it comes to assessing your health. Now let's have a quick look at some of the BMI alternatives available. In fact, combining BMI and some of the methods below will give you more insight into how much body fat you're carrying and testing your body composition.
Top 5 BMI Alternatives
1. Relative Fat Mass (RFM)
Unlike BMI, RFM doesn't use your weight in the calculation. Instead, it counts the distance around your waist (waist circumference) and your height.
RFM formula:
MEN: RFM = 64 – (20 x height/waist circumference)
WOMEN: RFM = 76 – (20 x height/waist circumference)
RFM is a good BMI alternative to decide if your body fat is at a healthy level. According to researches of 3,456 adult patients in the US, the RFM measurements nearly matched those taken by a high-tech DXA body scan. It is widely considered a great method to measure your body tissue, bone, muscle, and fat. This calculation will help people who are struggling with weight issues and have some health problems like high blood pressure or diabetes better track their body fat levels.
2. Body Adiposity Index (BAI)
The body adiposity index is used to check your body fat level based on the size of your hips and your height. Unlike BMI, it doesn't use your body weight for estimations. Several studies show that this method is equal to the body fat percentage of adult men and women.
BAI formula:
BAI = (hip circumference/(height)^1.5) - 18
hip circumference is in centimeters and height is in meters.
For example:
If your height is 180 cm hip circumference is 102 cm:
BAI = [102/(1.8)^1.5]-18 = 24.2%
BAI classification for women:
| Age (years) | Underweight | Healthy | Overweight | Obese |
|---|---|---|---|---|
| 20 - 39 | Less than 21% | 21% to 33% | Greater than 33% | Greater than 39% |
| 40 - 59 | Less than 23% | 23% to 35% | Greater than 35% | Greater than 41% |
| 60 - 79 | Less than 25% | 25% to 38% | Greater than 38% | Greater than 43% |
BAI classification for men:
| Age (years) | Underweight | Healthy | Overweight | Obese |
|---|---|---|---|---|
| 20 - 39 | Less than 8% | 8% to 21% | Greater than 21% | Greater than 26% |
| 40 - 59 | Less than 11% | 11% to 23% | Greater than 23% | Greater than 29% |
| 60 - 79 | Less than 13% | 13% to 25% | Greater than 25% | Greater than 31% |
3. Waist Circumference (WC)
Waist circumference measurement is often used to define your central obesity. While it's an old fashioned tape measure, it gives a good indication of the amount of abdominal fat that a person is carrying and determines the risk of heart disease as well as other weight-related conditions.
To get an accurate waist circumference:
Stand up, wrap a flexible tape measure around the widest part of your belly button. Position it correctly and make sure you remove any clothing around the abdomen. Breathe gently and see the result as you exhale. Do not hold the tape too tight or too loose.
For men: if the waist measurement is 40 inches or more, your risk for disease is higher than normal.
For women: 35 or more inches - indicate that your risk for health problems is higher than normal.
In fact, this measure doesn't measure your overall body fat percentage as it just looks at your belly button. The fat around the midsection is more dangerous than arm or leg fat.
4. Waist-to-Hip Ratio (WHR)
This is an effective way to calculate how much excess weight a person is carrying. Waist-to-hip ratio is often used as a measurement of obesity and a possible indicator of several health issues such as heart disease, diabetes, and high blood pressure. It is calculated by the ratio of waist circumference to hip circumference measurement in inches.
For example, if a person has a 30'' waist and 38'' hips, WHR = 30/38 = 0.78.
The figures in the chart below are based upon the standards set by the German Society for Sports Medicine and Prevention (DGSP).
| Men | Women | Category |
| <0.90 | <0.80 | Normal weight |
| 0.90 to 0.99 | 0.80 to 0.84 | Overweight |
| 1.0+ | 0.85+ | Obesity |
5. Hydrostatic Weighing
The hydrostatic weighing (underwater weighing) technique is used to measure your body density and composition. It uses Archimedes' Principle of displacement that an object displaces its volume of water.
To perform the hydrostatic weighing, you first need to weigh yourself on a dry land. Then, you will get into a large tank of water and sit on a chair placed on a zeroed out set of scales. Next, expel all the air from your lungs and stay still until the underwater weight is measured.
The resulting figures will then be used in special calculations to determine your percentage of body fat.
By volume, muscle weighs more than fat. This also means that a person with more muscle will weigh more underwater. And those who carry more fat will be more buoyant underwater.
The hydrostatic weighing method to analyze body composition is very accurate because the density of fat mass and fat-free mass remain constant while lean tissues like bone and tissue become denser in water. However, if you want to take the test, you need to understand its principles and do the calculations correctly.
Final thoughts
While BMI is a common method to assess one's body composition, it's not the be-all body assessment. So combining BMI and the top 5 alternatives above can give you an easier way to assess your health and any associated risks accurately. However, it's much better if you make an appointment with your doctor to get a more reliable and comprehensive picture of your health, weight, body composition, and weight-related risk factors.