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BMI: What does it mean and how to calculate the Body Mass Index

This is a very common question from boys your age. It may seem that the answer is simple, but the truth is that it is not so.

There may be differences based on body composition (amount of muscle, fat, and bone). It may depend on your genetics. But also the physical activity you do. It is possible that if you do a lot of sports you will have more weight, due to the development of muscle (which weighs more). And if you are out of shape and overweight with less weight it is because you have more fat (which weighs less).

Many changes take place in your body during adolescence. It is the moment of the “growth spurt” and it is possible that some of you will grow earlier and others later. This is due to hormonal changes that cause physical changes. At some point, if you have not given the growth spurt you can see yourself “fat”. Sometimes it’s a matter of waiting.

But for doctors and pediatricians it is possible to know if you are at a healthy weight. For this they use the Body Mass Index or BMI.

how to calculate bmi formula

What does the BMI indicate and how is it calculated?

BMI is a formula that relates weight and height. It is calculated:  BMI = Weight/ height 2

Example: If your weight is 45 kilograms and your height is 1.30 m, the BMI will be: BMI = 45 / (1.30) 2 = 45 / 1.69 = 26.63

This number is then fed into a BMI table (3) and tells us your percentile. Percentiles are used to compare a person’s measurements to others of the same age or gender. So if you have:

  • Underweight you are below the 5th percentile
  • Healthy weight: between the 5th and 85th percentile
  • Overweight: between the 85th and 95th percentile
  • Obesity: above the 95th percentile

They also allow you to check the evolution of your measurements, if you go down or up in percentile with age. To see in time that you are gaining weight and start prevention. Diet changes and increasing the level of exercise can correct it.

But it has its drawbacks:

  • If you compare yourself to kids your age, not all of you grow and develop at the same time. It is possible that some of you see yourselves thin and you find yourself in low weight. But this problem is usually transitory since when growth stops, the weight usually rises and returns to a normal level. Or the other way around that you look fat and that with growth the weight is balanced with the size.
  • It doesn’t tell you how much fat you have. You may have a high BMI because you have a large bone structure or a lot of muscle.

What is a body mass index chart?

Body mass index, also known as BMI, is a number that, for most people, accurately represents your body fat percentage. While there are several methods of measuring body fat, a body mass index chart is an easy and inexpensive way for adults and children to determine if they have a healthy body weight. The table simply uses a person’s height and weight to calculate a body fat percentage using a standardized formula.

Using a body mass index chart is simple. Many charts take the form of a grid with height measurements on the left side and weights at the top. A person, or their doctor, just needs to find their height and weight on the grid, which will then point to their BMI number. A body mass index less than 18.5 is underweight, between 18.5-24.9 is normal, 25-29.9 is overweight, and a body mass index greater than 30 is considered obese.

There are different body mass index charts for men, women, and children, each scaled to the average height and weight for each gender and age group. The formula for determining the body mass index depends on the measurement system used. To determine a percentage with metric weights, the BMI chart will display the results of body weight in kilograms, which is then divided by the individual’s height in meters. The resulting number is squared. In countries where pounds and inches are used, the percentage is determined by dividing the weight in pounds by the individual’s height in inches. This number is squared and multiplied by 703. This formula is used for all three BMI tables.

The whole notion of body mass index has been criticized by some within the medical and fitness communities. Some argue that a BMI chart doesn’t work well for fitness buffs or serious athletes with a high percentage of lean muscle. This is because the body mass index does not actually measure an individual’s body fat, but instead estimates body fat percentage based on a mathematical formula.

Another criticism is that some health professionals put too much emphasis on the percentage without considering other factors, such as genetics, lifestyle habits, stress, and previous medical history. The US Centers for Disease Control acknowledges these shortcomings and notes that the body mass index chart should not be the sole criteria used to determine whether someone is at a healthy body weight or at risk for disease.

So how do I know for sure what my weight is?

It will be the pediatrician or the doctor who will be able to tell you if you have weight problems. It is good that you talk to him if you think you have a weight or size problem.

It will weigh you, measure you and assess your pubertal development. They may ask you questions about your health, diet, and physical activity. He may also ask you about your family. Families share genes and life habits.

Once you gather all of this information, you’ll decide if you have a problem with your weight, growth, development, or disease.

He will tell you what you have to do: recommendations for food and physical exercise individually. Although if he thinks it necessary, he will ask you for some more tests or refer you to an endocrinologist.

This is better than fad diets, without control. There are young people who are obsessed with weight and develop anorexia or bulimia. In these cases it is necessary to have help to overcome them.

The Body Mass Index (BMI) is the figure that helps you find out if your body weight is adequate or not

In today’s post we want to explain what the famous Body Mass Index (BMI) consists of, which will allow you to know if your body weight is healthy based on a simple mathematical operation. It should be noted that this calculation is not recommended for children and adolescents due to their body development, but rather it is aimed at women and men over 18 years of age.

How to calculate the Body Mass Index

Calculating the Body Mass Index is very simple: it consists of dividing the person’s weight (in kg) by the squared height expressed in meters . Here is a practical example:

Marta weighs 64 kg and is 1.67 meters tall.

  • The height squared is 1.67 x 1.67 = 2.7889
  • The division to obtain the BMI would be: 64 kg / 2.7889 = 22.94

Martha’s BMI is 22.94

Next, once the result is obtained, it must be placed in the corresponding range of the BMI:

Body Mass Index
Under 18 weight below normal
From 18 to 24.9 suitable weight
From 25 to 29.9 Overweight
More than 30 Obesity

In this case, with a BMI of 22.94, Marta would have an adequate weight.

Aspects to take into account with the Body Mass Index

Calculating BMI is a useful tool to quickly find out if your body weight is, for example, in the overweight zone, but keep in mind that this index does not take into account the different densities of muscle mass, body fat or body mass. I mean. In the case of athletes who have a very developed muscle mass, the result of this calculation could erroneously indicate that they are overweight. Care must also be taken in the results obtained in pregnant or elderly people, since they are special cases and in any case other parameters should be taken into account to determine their BMI.

If you want to know your body composition with total accuracy, we recommend that you request free 30-minute nutritional advice from the Nutrition service of your DiR Club. Through this visit you will be able to know how the different types of tissues in your body are divided: fat, visceral fat, muscle, bone mass, water, etc. This way you can have an idea of ​​what the current state of your metabolism is and know what you have to work on through food.

Remember that maintaining a healthy diet and physical activity is essential to avoid risk factors such as cardiovascular disease, diabetes or obesity, among other diseases.

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