Did you know that obesity can reduce your life expectancy by up to 10 years?!


It also significantly reduces your disability-free life expectancy, that is the number of years you can expect to live without a disability.


What’s more worrying is that over 66% of the UK population are overweight, and just under 30% are classified as obese.


But fear not!


In this blog post, you are not only going to learn how to determine whether or not your weight is healthy, but you will also be given the tools to identify the factors affecting your health.



Introducing the Body Mass Index


Body Mass Index (BMI) is a calculation which measures your body weight in relation to your height.

BMI calculation

If your BMI is either too high or too low, you are exposed to an increased risk of developing various health conditions outlined below.


You can calculate your BMI using our calculator below.



BMI Calculator

Once you have your score you will be categorised into one of the following groups:

BMI categories

Let’s have a look at each category and what the potential impact on your health is.




Underweight (18.5 or less)


Being underweight can be equally as dangerous as being overweight. Common health risks associated with being underweight can include:


  • Weakened immune system
  • Nutritional deficiencies
  • Increased risk of osteoporosis
  • Fertility issues
underweight image
healthy BMI

Healthy (18.5-24.9)


This is the healthy weight range and means that you have a lower risk of developing health conditions as a result of your weight. Here are a few benefits of maintaining a healthy BMI:


  • Reduced risk of having a stroke/heart attack
  • Reduced risk of developing type 2 diabetes
  • Reduced risk of joint complaints
  • Less likely to experience complications during pregnancy and birth


However don’t get too comfortable, you can still be unhealthy & have a “healthy” weight. We’ll touch on this further on.


Overweight (25-29.9)


Whilst not as severe as being obese, being overweight comes with all of the same risks. Common health risks associated with being overweight/obese can include:


  • Heart disease
  • Stroke
  • Type-2 diabetes
  • Various types of cancer



overweight BMI
Obese BMI

Obese (Above 30)


Being obese comes with the highest risk of developing potentially life-threatening conditions. Common health risks associated with being overweight/obese can include:


  • 3x more likely to develop colon cancer
  • 2.5x more likely to develop high blood pressure, and therefore a higher risk of developing heart disease
  • 5x more likely to develop type 2 diabetes.


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The Limitations of Using BMI


If you’ve taken the BMI test, the chances are that you are either feeling pretty good about yourself, or pretty rubbish. But before you judge yourself, you must understand that there are certain limitations to using BMI as a health measure.


In some circumstances, it can even be completely inaccurate for some.


Let’s have a look at some examples.

The Obese BMI Paradox


Interestingly, there are some people who are classified as overweight or obese who are actually less likely to have a heart attack or die from other health issues. How can this be?


Let’s say we have two different people who are both 6 foot tall & weigh 90kg. One of them is a professional athlete who has a very low amount of fat on their body and a lot of lean muscle. The other is a sedentary office worker who is carrying a lot of excess fat, and a small amount of muscle.


These two people will have a BMI reading of 26, making them both classified as overweight. Yet it’s fairly obvious to see that the professional athlete is by no means overweight and likely very healthy, so how could they get this result?


Well, this is actually one of the main problems with BMI, it can’t tell the difference between muscle mass & fat mass.

BMI lifestyle comparrison

These two individuals weigh the same but both look completely different. One of them is slim & athletic, and the other is visibly overweight & unfit.


This is because muscle tissue is denser and takes up a lot less space than fat tissue. The BMI reading would be accurate to suggest that the office worker has high health risks but would be relatively inaccurate for the athlete. BMI simply can’t account for differences in body composition, and therefore may not be the most reliable indicator of health risks.


It is for this reason that we measure our client’s Waist-to-Hip Ratio as well as their BMI as this will tell us more about their body composition and risk of disease. You can read more about your Waist-to-Hip Ratio here.

MRI of thigh

The Healthy BMI Paradox


Now let’s look at another two people, this time they are both 6 foot tall & weigh 80kg.


One of them is a fitness instructor, who prioritises whole foods, consumes over 5 fruit and veg per day, exercises daily, and sleeps well. The other is a bar worker, who eats a lot of junk food, very little fruit and vegetables, rarely exercises, and has very poor sleep.


These two people would both have a BMI reading of 23.8, meaning both of them are classified as having a “healthy weight”.

healthy BMI comparison

However, despite them both having the same weight, each lives completely different lifestyles.


You could make the argument that the bar worker is actually very unhealthy and will have a lot of health risks, especially in comparison to the fitness instructor. Yet their BMI tells them that they have low health risks.


This is another problem with BMI, it can’t take into account all the factors that will affect your health. These two individuals weigh the same but both lead completely different lifestyles and therefore have different health risks.


You could be overweight on the BMI scale and very healthy, and you could be healthy on the BMI scale but actually you could be very unhealthy.


So why use this method in the first place?

Benefits of BMI


Well, BMI is actually a very quick and easy health indicator to use which is ideal for GPs who don’t have much time to treat individual patients. It’s also relatively accurate for the general population.


At HBS we have a little more time with our clients so we take a few more measures to get a good insight into not only your health markers but also your health behaviours. You can evaluate your own health behaviours by using our Health Level Calculator.


Although your BMI doesn’t tell the whole story of your health, it does provide a very key piece to the puzzle.

What Other Measures Can You Use?


BMI is just one possible tool you can use to evaluate your health, however, like most DIY jobs – more than one tool is often necessary and will allow you to do a better job.


  • The Waist-to-Hip Ratio (WHR) is used to identify how much fat you store around your midsection, which can also be used to evaluate your weight-related health risks. You can read more about the WHR here.

  • Progress photos are also useful as they provide a visual aid, allowing you to evaluate your body composition. However this is best used in conjunction with BMI & WHR. You can read more about progress pictures here.

  • If you want to find out the full picture of your health, then you need to take in to account the behaviours and actions that contribute towards your health. You can do this by using our very own Health Level Calculator. This will allow you to evaluate your health behaviours and highlight where you can improve.


Take-home points

At Health by Science, we recommend taking a variety of different measures, alongside taking your lifestyle factors into account as well.


This will allow for a more accurate estimation of your health, and also highlight what areas you need to improve on.


If you are interested in finding out how healthy you really are, then try out our free online Health Level Calculator.

image of weight loss scales


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