Why health is about more than your BMI

editors-picks Fitness Health & Wellness

By Liz Tyzack

29 July 2020

With the recent reopening of indoor gyms, studios, and pools in the UK, there has been a lot of talk in the media about weight loss. This has mostly centred around evidence that “being overweight or obese puts you at greater risk of serious illness or death from covid-19”.

The chief nutritionist for Public Health England told the BBC that alongside the widely-documented health benefits to losing weight, doing so may also protect people against the effects of coronavirus.

However, I have noticed that a lot of the discussion around health has been centred around a person’s BMI. Whilst this can be a useful metric in certain circumstances, it is not necessarily the only (or the best) way to determine a person’s health.

Beach exercise — Photo by Kaylee Garrett on Unsplash

What is the Body Mass Index?

Let’s start by looking at the use of BMI measurements. For those who haven’t heard of this, it stands for the Body Mass Index, and is used to determine if a person’s weight is ‘healthy’ based on their height. It was first created in the 1800s by mathematician, Adolphe Quetelet.

Whilst some research has shown that there are links between a person’s BMI and their overall health, there’s a lot of information it doesn’t take into account. For example, it is well documented that muscle weighs more than fat, as muscle is far denser; this means that if you had two equal sized bowls of muscle and fat, the muscle would have a greater mass and therefore weigh more. Aside from looking at a person’s actual fat to muscle ratio, their weight can fluctuate rapidly depending on external factors like: how much water they are holding, when they last ate, and when they last went to the toilet.

In order to fully understand why relying on body weight or BMI alone to determine health is flawed, we need to look at the index in more detail. If you search for an image of the BMI, you will be met by a colourful chart, with height along the y axis, and weight along the x; the subsequent grid shows the intersection between a given height and weight as a value between 9 and 65. The values are then broken down into five categories: Underweight (9-18), Healthy (19-24), Overweight (25-29), Obese (30-39), or Extremely Obese (40-65). Some quick maths will tell you that the ‘Healthy’ range of the chart makes up only 10.5% of the total range of results. This proves to me what I already suspected: it’s statistically very difficult to fall within the categorised as Healthy by this system.

The best way to assess how this chart works in practise is to try it out for myself; so, I put my details in to the NHS BMI Calculator, to see where I sit on the chart. Obviously I won’t be telling you my height and weight (that’s a bit TMI for this platform), but I will explain a bit about myself for context: I have danced since the age of 3, I am a qualified fitness instructor, and I currently workout 5 times a week. I also have a personal interest in nutrition, so eat a fairly balanced diet (with the occasional glass of vino and take away, of course).

Despite leading a fairly healthy, and active life, according to the calculator I am Overweight. Though I don’t know my exact body composition, I would guess this is due to a combination of my height (I have been lovingly called ‘vertically challenged’), and the fact that I carry quite a lot of muscle from both my training background and genetic make up. Nonetheless, when I have told those close to me that I am technically Overweight, I have been met with disbelief.

Embrace the power of a bike — Cropped shot of women working out with exercise bikes in a exercising class at the gym

Is ‘Body Fat Percentage’ better?

So, if using BMI isn’t a reliable measure of health, how can you know if you’re ‘healthy’? One alternative, if you want a numerical value is looking at your Body Fat Percentage; whilst calculating this does still use your weight, it also takes in to account your waist circumference, as well as your wrist, forearm, and hip circumferences for women. By using the linked calculator, my body fat percentage came out as ‘Acceptable’/average (the exact name of the category depends on the website you look at, but the range remains the same). Bear in mind when calculating this, that the remaining percentage after fat is not entirely muscle; it will also include your bones, organs, and water weight.

A lot of conversations about weight loss tend to make out that body fat is a bad thing, and that it can only mean poor health. But it’s important to remember that fat is crucial for our bodies. It keeps us warm, it protects our organs, it gives us energy, and it carried essential fat-soluble vitamins. For women, sufficient body fat is essential for healthy menstruation; too little, and menstruation can stop (Amenorrhea), which can affect fertility long term. Because of this, whilst the ‘average’ range for men is 18-25%, whilst the female equivalent is 25-31%.

Although generally this calculation gives a better insight in to what is going on inside the body, it’s still not necessarily the right metric for everyone. Whilst it removes the issue of muscle weighing more than fat, it still only gives a very basic idea of what is actually going on, as no two people are the same. It is very likely that there are a lot of people who would technically class as ‘Obese’ by this scale, who actually lead very healthy lives. Certain bodies simply hold on to more fat naturally, meaning that two people with the same weight and measurements may actually have different fat percentages. Whilst there are more precise ways of testing body fat percentage (such as MRI or CT scans), the calculator I used here is not an exact science- especially as it does not account for activity level, age, or ethnicity. Therefore, it is still not necessarily the best way to judge a person’s overall health.

But what is ‘healthy’, if not a number?

There are countless ways you can assess a person’s health, but at the end of the day there is no ‘one size fits all’ method for doing so. Despite what the media regularly tries to tell us all, healthy is different for everyone. There are so many more factors that make up a healthy human than the number on the scale, your BMI, or even your body fat percentage. Just a few examples are: the types of food you eat (instead of the quantity), the amount of sleep you get, genetics, the type of exercise you do, and mental health. Not only that, but there’s hundreds of different ways you can lead a healthy life.

As well as focusing on weight, the media also emphasises the need for specific types of exercise, and a rigid calorific intake as the goal. But again, no two people need the same amount of calories a day, and no two people will enjoy/benefit from the same exercise routine. It takes time to find what healthy is for you, it truly is a balancing act that will change and evolve as you move through life.

For me personally, healthy will always be a feeling, not a number. It is a combination of my outlook on life, my comfort level, and believing that I know what is best for my body. For some people, that does involve numerical data, and calculations like BMI and body fat percentage, and that’s absolutely fine. But if that doesn’t work for you, try looking for qualitative results instead of quantitative. Ask yourself questions like: “Am I happy?” “Am I comfortable?” “Am I eating in a way that fuels and satisfies me?” “Am I able to move in a way that feels good for me?” To me, that is the true meaning of health- not a number on a chart designed two centuries ago by a mathematician!