How do you know your ideal weight? People’s morphology is different, muscle and fat mass are different depending on whether you’re a man or a woman, and there are also differences based on our age. So how do we get an idea? There are two indices that can help us with this by verifying if our weight is located within a normal (healthy) range compared to undernutrition or excess weight.They’re the body mass index and the fat mass index, and they’re relatively easy to calculate. While the interpretation of the results is done using intervals, they give a good indication of where you stand with respect to your weight, height, gender, and age.
The BMI (Body Mass Index) indicator lets you check if your weight is appropriate for your height. It’s been validated by the World Health Organization (WHO) for people between 18 and 65 years of age. For children, there’s a growth curve that gives a better indication, and serious athletes, who have developed muscle mass, and pregnant women can’t use this indicator to establish their ideal weight.
Simply divide your current weight by the square of your height:
BMI = Weight/(height x height)
Here’s an example: weight = 69 kg; height = 1.77 m
BMI = 69/(1.77 x 1.77)
BMI = 22.02
Once you’ve calculated your BMI, you can interpret your result using this list:
< 16.5 = starvation
16.5 to 18.5 = underweight
18.5 to 25 = normal weight (our example)
25 to 30 = overweight
30 to 35 = moderate obesity
35 to 40 = severe obesity
> 40 = morbid obesity
While BMI gives a certain indication regarding your ideal weight with respect to your height, it’s not accurate enough if we know that men and women have very different morphologies and that there’s also a certain number of differences according to age. For a bit more accuracy, after calculating your BMI, you can calculate your fat mass index, or FMI. This index is expressed as a percentage and shows the difference between the fat mass and the muscle mass of the body.
The formula for calculating your FMI takes into account your BMI, your age (in years), and your gender (0= woman and 1= man), and the figures are constant values:
FMI = (1.2 x BMI) + (0.23 x age) – (10.83 x gender) – 5.4
Here’s an example: the BMI from the previous example = 22.02; for a woman (=0); 34 years of age.
= (1.2 x 22.02) + (0.23 x 34) – (10.83 x 0) – 5.4
= 26.424 + 7.82 – 0 – 5.4
Once you’ve calculated your fat mass index, you can interpret your result using this list:
For a woman:
< 25% = too thin
25 to 30% = normal (our example)
> 30% = too much fat
For a man:
< 15% = too thin
15 to 20% = normal
> 20% = too much fat
These two easy-to-calculate indices give an interesting indication of where you stand with respect to your weight, height, age, and gender.
While they give a good indication, they don’t reflect the different characteristics of each person’s morphology and anatomy. That’s why serious athletes can easily find themselves in the obesity category, since muscle weighs a lot and their muscle mass is significant. Likewise, certain people have bones that weigh more than others, or have more or less muscle. That’s why, as we’ve explained above, it’s not recommended to use these indices for children, athletes, pregnant women, and the elderly, because they don’t accurately reflect reality.
If, for example, you find yourself in the normal weight range, which corresponds to a healthy weight, but you nevertheless want to lose a few pounds or else put on some weight, make sure you don’t drastically change categories. For the vast majority of people, these indicators are effective.
A little tip: you can use these indices in different ways – for example, by calculating your BMI and your FMI with the weight that you want to have in order to determine if your expectations are realistic in terms of health.