What is Body Mass Index (BMI) and does it matter?

What is Body Mass Index (BMI) and does it matter

Body Mass Index (BMI for short) is a measure of your body fat, in relation to your height and weight. Doctors and medical practitioners use it during consultations. In this article we look at BMI – what it is, how to calculate it and consider why you might be interested in your BMI.

What is body mass index?

Body mass index (BMI) is a relatively simple tool that you can use at home. It helps to give you an indication of whether you are a healthy weight for your height. BMI tools or calculators generate a single numerical value, which is then classified into four main groups:

  • Underweight – below 18.5
  • Healthy – 18.5 to 24.9
  • Overweight – 25 to 29.9
  • Obese – over 30

The aim is to find yourself in the “healthy” category. Medical practitioners believe that people with BMI´s in the overweight or obese categories are at greater risk of health problems and chronic diseases. Remember, being underweight is also not healthy.

Note, BMI is simply an indicator of body fat. It does not directly measure body fat.

How do I calculate my body mass index?

For adult men and women, BMI is calculated as follows:

Weight (kilograms) is divided by your height squared (metres).

You can find lots of online BMI calculators to do this calculation for you. For example, this one from the UK NHS (external link).

You can also work it out for yourself. If you want to do it now, measure your height in centimetres. Measure your weight in kilograms. For example, say you weigh 75 kilograms and you are 1.7 metres tall. To work out your BMI you would do:

  • 75 divided by 1.7. This equals 44.1
  • Divide 44.1 by 1.7. This equals 25.9. This is your BMI. This measurement means you are in the overweight category (just!).

For children aged 2 to 18, you will need a child specific calculator. (There is one of the NHS page link above).

Note, BMI does not take into account ethnicity, age, body composition or gender. It is also not valid during pregnancy.

Body fat and body muscle

BMI is a useful indicator of your body fat but try not to get obsessive about it. The tool is so easy to use that you can do it any time at home. There are other more sophisticated ways to measure body fat, but most of them will require some sort of machine, which means it will cost you money.

It is simple to use BMI to measure changes over time – this can give you motivation for taking action! Also, you know that if your weight starts to drop, your BMI will also start to drop (once we reach adulthood most of us stay the same height!).

However, BMI is still a relatively crude measure of your body fat. Other measures are also useful.

Most health guidelines recommend that you look at your BMI measurement together with a measurement of your waist circumference. Waist circumference is an indicator of how much excess fat you carry around your waist. Generally, the larger your waist circumference the higher your risk of health problems and chronic diseases. Most health professionals agree that where you store fat can affect your risk of health problems.

In the UK, the NHS suggest that you need to lose weight if your waist circumference is:

  • Females: 80cm (31.5ins) or more
  • Males: 94cm (37ins) or more

So, if are female and your BMI is 25 or higher and your waist circumference is greater than 80 centimetres, it would be a good idea to start to lose some weight.

One of the limitations of BMI is that it does not take into account how your body is composed – how well developed are your muscles? Muscles are much more dense than body fat, which means that muscle weighs heavier than body fat. Body builders, athletes or others who are very muscular might be classified as “obese” by the BMI calculator, whereas when researchers measure their actual body fat it is the healthy range.

Weight gain, in simple terms, happens for many people when they eat more calories than they burn. The most sensible approach to weightloss is to take up or increase your level of exercise and to reduce your calorie intake. Get realistic about what you actually eat – many of us tend to under-report what we eat. Simply taking a smaller portion at meal times and walking for 30 minutes a day can help us to start to drop weight. Slow and steady weightloss is ideal.

Detox and weightloss retreats at La Crisalida

Juicing is a great way to start the weightloss process. We suggest three days is a place to start. Juicing means you can easily keep track of the calories you are consuming, so you can make sure you stay on track during the day. At the same time it delivers fantastic nutrition to the body, so your body gets all the vitamins and minerals it needs for proper functioning.

Following a balanced plant-based diet can also help with weightloss. This is not a restriction diet, you get to enjoy a variety of dishes, balancing protein and carbs intake (read our article about good carbohydrates to include in a plant-based diet here). If you need inspiration, we have published lots of recipes on our blog page (click on the words “food recipe”). If you need a kick-start, come to La Crisalida Retreats for one of our detox and weightloss retreats.

About the author

Lisa is one of the founders of La Crisalida Retreats. She is an Epidemiologist, therapeutic hatha and yin yoga teacher and also teaches mindfulness meditation. Lisa has studied NLP and hypnosis, as well as nutrition (she designs the menus).