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Understanding diabetes

Calculate your Body Mass Index (BMI) and Prevent Type 2 Diabetes

Learn how to measure your body mass index (BMI) and see if you are living a healthy life.

Richard Johnson
Reading time: 
6
minutes
Published: 
May 23, 2022

The healthier your life, the greater your quality of life and happiness, so why be unhealthy? You can reduce the risk of many preventable diseases, such as type 2 diabetes, simply by eating healthily. The question is, how do you know if you're living a healthy life? 

We all know the theory, that staying active and eating nutritious food fairly obvious, but what is defined as healthy changes over time as the science improves. What your parents or grandparents thought was healthy back in their day is very different from what is considered healthy by today’s standards.

There's more to a healthy lifestyle than a number on a bathroom scale.  If you want a concrete answer to the question, “how healthy am I?” Then you have to turn to science to measure your health and understand what is considered healthy and why. 

Perhaps the best way we have to measure health is to calculate your BMI. Unfortunately its not that simple, BMI is more of a statistical tool than a diagnostic tool, originally designed to compare different population groups; in isolation, BMI is not designed to determine whether you are healthy or not. However, there are ways to address this issue, but we’ll come back to this later in the article.

The Body Mass Index (BMI) can be used as a guide to assess whether there is a healthy relationship between your height and your weight. By calculating your BMI, you can determine whether you are underweight, of normal weight, overweight or obese.  

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How is my BMI calculated?

You can easily calculate your BMI below, it will even return your status.

What the calculator is doing is as follows:-

BMI = your body weight in kg / (your height in m)²

So, for example, if you are a man who weighs 85 kg and has a height of 1.78 m, your BMI would be:

85 / (1,78)² = 26,827 

You can look up this figure using the relevant BMI chart, considering age, which would indicate what a normal weight BMI should be. Both men and women measure their BMI using the same formula - and should use the same BMI table.

DiabTrend’s own BMI calculator

If you want to calculate your own BMI quickly then just fill in your height and weight below in our handy BMI calculator. 

Don't lose heart if your BMI categorises you as either overweight or underweight. Getting to a normal weight is not as difficult as you might think. Learn how to live a healthier life with a Mediterranean diet and DiabTrend, and prevent type 2 diabetes.

DiabTrends BMI Calculator
System:
Weight (KG):
Height (CM):

How do you use BMI?

The BMI scale is thus for adults (+19 years and not pregnant):

BMI below 18.5 = underweight

BMI between 18.5-24.9 = normal weight

BMI between 25-29.9 = overweight

BMI between 30-39.9 = obese

BMI over 40 = severe obesity

Put simply, too high a BMI indicates that your weight is too high. And the same goes the other way around. If your BMI is too low by standard, it means you're underweight. So there are very specific measures of what your weight should be in relation to your age, sex and height. 

BMI can be used as a screening tool, but it cannot be used completely to diagnose obesity or health. This is because the actual fat percentage is not measured directly - a little more information is needed.

What is a healthy BMI?

One of the benefits of BMI is that it provides some pretty accurate figures for when you're at the healthy end and when you should consider going on a diet. BMI measures are best for men and women aged 20 and over.

BMI is divided into different groups that show which weight category you belong to. This BMI scale shows the BMI for adults over 18, but you should be aware that it is only indicative. For example, if you are heavily built, your BMI may be over 25 without being overweight.

What about my muscle mass and fat percentage?

BMI is a good way to get an idea of how healthy you are. But it's not the only way. If you want an accurate picture of your body and your diabetes risk, you need more than your BMI. For example, when you calculate your BMI, it doesn't consider your muscle mass. So you can easily be categorised as overweight according to BMI, even if you exercise a lot and therefore have bigger muscles. There are a few different ways you can get a more accurate picture of what your fat percentage actually is. 

You can also use the more detailed formula developed by the U.S. Navy. 

Perhaps the best way, from the perspective of someone with type 2 Diabetes is to calculate your fat percentage in combination with your BMI number and your age. This is perhaps a better measure for diabetics because the measurement of fat is a better measure of diabetes risk than BMI alone. The formula is as follows:

Fat percentage = 1.2 x BMI + 0.23 x age - 10.8 x gender- 5.4

Here "gender" should be replaced by a 1 if you are a man or a 0 if you are a woman.

So, if you are a man with a BMI of 23.1 and an age of 30, the calculation will look like this:

1.2 x 24.1 + 0.23 x 28 - 10.8 x 1- 5.4 = 19.2%

So you would have a fat percentage of 19.2%. Mr. Normal weight!

The ideal fat percentages

Through countless studies of the human body, scientists have worked out what the ideal fat percentages should be for men and women. So it's possible to find out what separates the regular person from the 100-metre athlete.  

A normal fat percentage for men and women would be as follows:

Description Women Men

Essential fat 10-13% 2-5%

Athlete 14-20% 6-13%

Fitness 21-24% 14-17%

Normal weight 25-31% 18-24%

Overweight 32% or more 25% or more

Source: American Council on Exercise

From the table above you can see that the relationship between health and fat percentage also depends on gender. For example, women tend to have more body fat than men.

So from this chart, you can compare your own body fat percentage with the standards. If we continue with the example from before, a man with a fat percentage of 18.4% would be declared average. However, it is not far from the average fitness guru, and thus this man can pat himself on his muscular shoulders.

If I, as an athlete - or just someone with a lot of muscle - have a BMI above 25, am I still overweight?

If you follow the standards arrived at through studies, the answer is "yes". If you have a BMI of 25-29.9, you are considered overweight, and if you have a BMI above 30, you are classified as severely overweight. On the other hand, if you have a BMI below 18.5, it is classified as underweight.

However, as mentioned earlier, this is not necessarily accurate. However, you can still have a high BMI even if you have a high muscle mass rather than a high-fat percentage. To get a sure answer about how healthy you are and what the risks might be, you should be checked by a healthcare professional.

Does BMI work the same way for children and teenagers as for adults?

Yes, BMI works the same way for children and teenagers as for adults. But unlike BMI testing for adults, which only looks at height and weight, age and gender are also important when calculating the BMI of teenagers and children. This is because body fat changes with age, and the amount of fat varies between girls and boys.

So again, it may be more accurate to use the more advanced BMI formula, where you take into account both age and sex.

How good is BMI as an indicator of body fat?

BMI (body mass index), which is based on the height and weight of a person, is an inaccurate measure of body fat content and does not take into account muscle mass, bone density, overall body composition, and racial and sex differences.

There is a strong correlation between BMI and body fat, but even if two people have the same BMI, this does not necessarily mean that the level of body fat is the same.

In general, these caveats should be taken into account:

  • At the same BMI, women tend to have more body fat than men.
  • For the same BMI, older people tend to have more body fat on average than younger adults.
  • At the same BMI, athletes have less body fat than non-athletes.

Are there other ways to estimate my body fat percentage besides BMI?

The only other accessible way to measure body fat is by using a calliper to examine the thickness of skin folds in 2-4 places on your body. Other methods are just too expensive or inaccessible (DEXA, BIA, BOD POD).

What are the disadvantages to BMI?

The BMI (Body Mass Index) only takes into account the height and weight of a person, it does not take into account body fat, muscle mass, bone density or body composition. There are also differences between gender and race. The problem with this is that two people can have the same height and weight, but they don't have to be equally healthy. One may have a high muscle mass, while the other person's body has a higher fat percentage.

BMI does not take into account muscle mass or the distribution of fat on the body. If you have large fat deposits centred around your stomach (apple shape), this can be dangerous, even if you have an otherwise normal BMI. In such cases, your waist circumference should also be measured and considered alongside your BMI.

Your weight is not the only indicator of your health. Your genes, lifestyle, diabetes risk, heart function, activity level, etc., are also important to consider when assessing your health.

If you calculate your BMI and decide that you want to change your lifestyle based on this and achieve weight loss, you may have the same BMI after a month, even if you have lost weight. This is because your fat has been replaced by muscle, so BMI can be confusing, so increasingly, doctors are warning against using BMI alone. 

BMI across cultures

BMI is easy to understand because it takes into account both age and gender. However, the measures set do not consider all ethnicities and cultures. In other words: A typical adult male in Europe probably looks a bit different from a typical adult male from the Philippines. If you are of African or Asian ethnicity, you should be aware that a BMI of 23 may be at risk. Therefore, you should always aim for a BMI below 25 - preferably 23.

BMI was created from the studies done in Western countries, so this is also something you need to take into account

Why is it important to know your BMI?

BMI should only be used as an indicator and preferably in conjunction with other tests - such as measuring body fat with a calliper.

It means you've taken an interest in your body fat percentage and your health. And that's necessary because there are a whole range of problems associated with being overweight (and underweight).

Conclusion

BMI is therefore a method that allows you to calculate whether you are normal, underweight, or overweight. This means that if you have any doubts about your health, just calculate your BMI based on your height and body weight. If you are worried about diabetes, it's best to use a BMI calculation that considers body fat, such as the US Navy formula mentioned above.

There are some set standards to compare yourself against. If you are female and have a fat percentage of 25-31%, then you are perfectly normal. The same goes for a man with a fat percentage between 18% and 24%.

The fat percentage can be calculated by either having a health professional measure your fat with a fat caliper. Alternatively, you can measure it yourself using a slightly more complicated formula, which we’ll come back to.

The body mass index (BMI) is not in itself the definitive answer to the question, “how healthy am I”? Many people consider BMI to be too simple and not accurate enough, as it only focuses on height and weight. This means that two completely different people can have the same BMI, even if one is twice as round as the other.

Thus, BMI should be used as a starting point. BMI can give you a first-hand insight into your state of health, and then you can go to an expert for a more comprehensive answer.

Calculating your Body Mass Index is the first step in making sure you reach your ideal weight.  The next step is to review your diet and adopt a proven strategy for weight loss, such as the Mediterranean diet, which coincidentally is the secret to a long healthy life.

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