Body Mass Index for Children

Exercise

With more and more infectious viruses developing every day, disease control in children is now difficult than ever. What really helps them fight these germs and keep themselves safe is a strong immune system. 

This directly correlates with the health of your child. The sooner you start to pay attention and encourage your child to develop some healthy habits, the better it is. But how does one get an estimation of whether or not their child is healthy just by looking at them? 

To solve this problem, healthcare professionals use a term called BMI (body mass index) to get a rough idea about your child’s weight. 

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If you take your child to a pediatrician on a regular basis, you might have heard about this term too. In this article, we will find out more about this metric and understand how a BMI rating helps assess the health of your child. 

Keep on reading to know more. 

Body mass index : At a glance

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BMI body mass index (metric formula) written on a notepad sheet.

The formula for body mass index was given by a Belgian astronomer named Lambert Adolphe Jacques in the 1830s. Scientists have now been using it for more than a century to determine the fat percentage in one’s body. 

Scientifically, the term BMI refers to the result obtained by dividing a person’s height in meters to the square of their weight in kilograms. The value is then put against the standard value for that particular age and gender. 

In simple terms, it is an indicator of the amount of fat tissue present in one’s body.  

  • BMI = Weight in kilograms/ Height squared in meters 

After the analysis, an individual can get the following results : 

BMI rangeWeight rangeRemarks 
Less than 18.49Below normal weight Proper dieting and an increase in daily calorie intake is for gaining weight
Between 18.49-24.99Healthy weight Healthy and fit body, need some amount of exercise regularly to maintain this BMI level 
Between 25-29.99Slightly overweight Taking a couple hundred calories off  your daily intake and mindful eating is required 
Between 30-39.99Highly overweight or obese category Person is likely to develop chronic diseases if they do not begin to exercise 
More than 40Morbidly obese Health conditions such as type 2 diabetes, cardiovascular issues and lack of mobility can be seen 

There were no computers or technological gadgets when Quetelet came up with the BMI formula, therefore he came up with a straightforward approach. However, with time, scientists enunciated that this formula had a few pitfalls too. For instance, it treats the human body as a two dimensional entity and does not take into account factors like fat tissue percentage or bone density. 

This caused short individuals to underestimate their weight whereas taller people would think that they are fatter than they actually were. To compensate for this anomaly, Nick Trefethen, an Oxford University mathematician, stated that the weight factor be further multiplied by 1.3 when calculating BMI. 

This does bring the error down to some point but the mathematician always believed that the human body is too complex to be analyzed quantitatively. 

Flaws in BMI calculation 

When interpreting fitness levels through BMI, it is hard to distinguish between body fat and muscle. For instance, a regular person who does no exercise and weighs 90kg could have the same BMI as that of an athlete who works out regularly. 

This is mainly due to the fact that muscles are roughly 18 percent more dense than a fat tissue of the same weight. As per the expected consensus, people who do not have a normal BMI are said to be unhealthy. However, as per a study conducted in 2016, BMI results showed wrong results for more than 75 million individuals. 

The ideal healthy weight for a large population is difficult to figure out. Not only is it dependant on factors like bone density, body type, muscle-to-fat ratio, sex and age, having one ideal score range for everyone is also not fitting. 

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BMI is only there to give us a rough idea of a child’s health but is not something which can be relied upon blindly. For this reason, many pediatricians use multiple methods to determine the fat levels and body composition of kids. We will be discussing these methods later in this article.

Male vs female BMI : How do they compare 

If you notice the BMI chart of a male and a female child, you will notice that there are differences in the value of BMI for the same height and age group. Men always tend to have slightly higher values than women. Why does this happen? 

Even though the differences are not that major, the slight shifts are due to the following reasons : 

  • Proportions : Some individuals have shorter arms and longer legs, whereas the case might be totally different for another person. This alters the distribution of muscle and fat in the body.
  • Muscularity : A male body is usually more muscular than that of a woman, which adds to a higher percentage of lean body mass. Women tend to have more fat whereas men have more muscle. 
  • Shape of the body : The shape of our body helps determine the way we carry our weight. Most women have pear shaped frames whereas men have a rectangular body and broader shoulders. 
  • Age : The older a person gets, the more fat he/she is able to store inside their body, leading to a higher BMI value 
  • Fat storage : Women tend to have 5-11% more body fat than men in areas like thighs, torso and buttocks. 

Despite these differences, BMI is calculated using the same method for both genders which brings some degree of discrepancy in the values. 

How accurate is BMI for children

Most adults stop growing after 23 years of age, unlike children who show changes in their body on a frequent basis. When calculating BMI for adults, we don’t take a child’s gender and age into consideration. On the contrary, the calculation is slightly different in case of children and teens. 

The growth rate of a girl is slightly quicker in comparison to a boy. Owing to this, healthcare professionals also take their sex and age into consideration. Categorizing children by weight ranges is something which doctors often avoid, the reason for this is threefold : 

  • Children change with each month of their age 
  • Their bodies change at different rates, even for the same age 
  • Girls usually grow taller at a faster rate as compared to boys

To account for this change, doctors calculate the BMI of children and compare the value to a sex-specific BMI-for-age chart. This gives them a BMI-to-age ratio which is an indication of whether or not your youngster is healthy. 

The steps to do this are : 

  1. Calculate BMI using a reliable BMI calculator. 
  2. Now navigate through the CDC growth charts and compare that value to other kids to see if your child has suitable weight for his/her age. 

This is the chart for girls aged 2-20 years. 

This is the chart for boys aged 2-20 years. 

  1. Interpret the results using the following table : 
Person’s weight BMI percentiles 
Underweight Value lies under the 5th percentile 
Healthy weight Value ranges from 5 to the 85th percentile 
Overweight 85-95th percentile 
Obese Value is equal to or greater than the 95th percentile 

BMI : Only a small piece of one giant puzzle 

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measurement of bmi. Body mass index

In the case of children, BMI values are correct up until a particular range. It is a good indicator of a child’s body fat, at least in case of  children who are overweight. In certain circumstances, it may also be incorrect. 

If a particular teen has an athletic build or plays sports on a regular basis, his/her BMI might be mistaken for overweight due to the extra muscles in their body. That said, if you feel that your child’s BMI levels are way out of range, you should definitely consult your physician. 

If a child has low or high BMI, then medical experts may also consider factors such as : 

  • Recommending other health screenings
  • Changes in diet 
  • Increase in physical activity 

Alternatives of BMI for younger children 

Aside from BMI, the following methods can be used to determine the weight range of your child : 

Air-displacement plethysmography 

In this method, children are made to sit in a small chamber while they have a bathing suit on. A computer then estimates their weight and body composition based on the differences in pressure and volume of air inside the chamber before and after they sit in there. This method is highly accurate and also very comfortable when it comes to kids. The only downside is that it is a bit expensive. 

Waist Circumference Measurement 

The excess fat located around the center of the abdomen is a significant determinant in body fat distribution. This method is carried out by measuring the circumference of one’s waist. The circumference is calculated by taking a measurement around the umbilicus, natural waist and the narrowest part of their midsection. 

This method is also very inexpensive but no standardized procedure for measurement has been introduced yet. 

Waist-to-hip ratio 

This method is primarily used to measure abdominal obesity. If you want to find out your waist-to-hip ratio, just take your waist measurement and divide it by your hip measurement. However, this method is highly prone to errors because it requires you to take two sets of measurements. 

Skinfold method 

In this method, a calliper is used to pinch out a certain portion of the skin to get an idea of the fat percentage in that particular area. It is a fast & easy method and is also relatively cheaper than other methods around. 

Bio-electric Impedance 

This involves passing electric current from one point of a child’s body to another and measuring the impedance that the current faces. Do not worry though, the current is really light and will not harm your child in any way. 

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Body fat analyzer. Isolated on white.

The time taken by the signal to reach one point to another helps doctors to determine the concentration of fat tissues which hindered the movement of the current. 

Benefits of a healthy BMI percentile 

Although BMI is not the only measure to assess one’s body health, maintaining a good BMI and keeping it in the normal range has numerous benefits. If your child has a high BMI at a young age, then he/she is most likely to develop serious health conditions down the road. 

Some advantages of having a low body mass index are : 

  • Reduced probability of joint and muscle pains
  • High energy levels and endurance 
  • Healthy circulation of body fluid 
  • Minimal digestive problems 
  • Improvement in sleeping pattern

On the other hand, having extra weight has the following effects on your body : 

  • Your child’s heart will have to pump blood at a faster rate due to low energy levels 
  • Blood cholesterol levels and triglyceride levels are spiked up 
  • Extra fat lowers the amount of good cholesterol in our body 
  • Your child will be vulnerable to poor stamina and serious health problems 
  • Increased risk of medical conditions such as : Gallbladder disease, sleep apnea, respiratory problems, high blood pressure etcetera

Tips to keep your body mass index in check

  • You should serve 5 meals every day and 3 out of those five should include veggies. Even if your kid does not like them, keep serving on a regular basis and your child will begin to eat.
  • Put a parental lock on all the smart devices in your home and set up a screen time limit. This ensures that they do not delve into a sedentary lifestyle. Rather, you can encourage them to read books and play outdoor games instead. 
  • An hour of physical activity is highly imperative for children of all ages. You can also include some strength training exercises in their schedule as they grow up. 
  • Drinks like lemonade, fruit punch, tea, soda and coffee should be avoided at all costs. They have a high quantity of sugar. Water and reduced fat-milk are better alternatives. 

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