BMI Measurement

Is BMI Accurate?

At some point in our lives we have all tried to lose weight. Many of us are still struggling down this meandering weight loss path filled with obstacles, detours and ill-informed advice that never seem to get us to that “ultimate weight loss goal”. You might even have been asked what  your BMI (Body Mass Index) is, with which you reply with shrugged shoulders.

In order for us to have a clear obtainable goal to focus on, we should start by asking the right questions. How much should I weigh? Is weight really the correct indicator of a healthy lifestyle?

Now the answer to this question is going to be very different from individual to individual, depending a quite a couple of variables. In order for us to calculate a “healthy weight” it is usually done with a formula that takes into account your height to weight ratio. This method is known as your BMI(Body Mass Index). But is BMI really the most accurate way for measuring whether or not you are over weight? Lets have a look at how BMI works.

What is BMI?

BMI is a way of measuring the amount of fat in a person’s body. The BMI sum outcome is then used to decide whether a person is overweight or underweight by looking at a chart.


How is it calculated?

To calculate your BMI, take your body mass divided by the square of your height, this will give you your BMI in kg/m2. Ok so you nearly fell of your chair when you saw the equation that seems to be something taken from an Einstein journal. Don’t fret to much about it, let’s take a look at 2 real life examples. Ruth weighs 64kg and is 1.68m tall. For her to work out her BMI she takes her height and multiplies it by itself (1.68 x 1.68 = 2.8224) she then takes her weight and divides it by this new value (64/2.8224 = 22,67) this means her BMI will be 22.67kg/m2. Ruth is pleased to see she fall in the “healthy weight” category according to the BMI chart. Underweight 16kg/m2 to 18.5kg/m2 Healthy weight 18,5kg/m2 to 25 kg/m2 Overweight 25 kg/m2 to 30 kg/m2 Obese 30 kg/m2 to 35 kg/m2 On the other hand we have Jason. Jason weighs a sturdy 80kg and is only a tad taller than Ruth at 1.69m. Jason is a fitness addict and workout 5 times a week and follows a very healthy diet to accompany his rigorous exercise regime. But there is a problem with Jason’s BMI measurement. According to the BMI chart Jason 28kg/m2 reading means he is overweight, but in fact it is exactly the opposite. The problem using BMI only As I said previously each individuals weight-loss goals will differ depending on a couple of variables.

This is exactly why BMI is not the end all and be all of weight-loss measurement. BMI only takes your weight (kg) and height (m) into consideration, but individuals vary in bone density and muscles weight. In the fitness industry we divide individuals into different categories dependant on exactly these variables. For instance an “Ectomorph” is a typical skinny guy. Ecto’s have a light build with small joints and lean muscle. Usually ectomorph’s have long thin limbs with stringy muscles while on the other side of the spectrum we have the Mesomorphs whom has large bone structures, large muscles and a naturally athletic physiques. But more on this in a future article. As you can see a person who is more muscular would tend to be classified as overweight, as in Jason’s case, or obese according to their BMI due to their excess amount of muscle and bone density.

The same counts for weighing more on the scale. It doesn’t mean they have more body fat just because they weight more than someone their same height. That’s why BMI might not be the most accurate way to determine if you are under or overweight. BMI also tells you nothing about where your body fat storage lies, for example around your stomach, or your thighs. It’s more important to see where you store fat than the absolute amount of fat when it comes to measuring certain health risks, especially heart disease. So what is the correct way to measure if you are under or overweight? A more accurate way to measure your under or overweight status is to do a body fat percentage test. It is a skin-fold test, whereby your skin/fat is pinched by a calliper at many standardised points on the body to determine the thickness of your fat layer. These measurements are then used with standard formulas to give you an estimated body fat percentage. This is simply the percentage of fat your body contains, and it can be a powerful indicator of your health. Too much body fat on the outer layer is a good indication of organ fat(fat located around your organs)that is linked to chronic health problems like high blood pressure, high cholesterol, heart disease, diabetes, and cancer. Too little body fat is also not good and can cause your body to enter a catabolic state, where muscle protein is used as fuel.

The only downfall of the body fat % test is that the accuracy of the measurement is very important. It is dependent on a person’s fat distribution, the technique, type of calliper and person’s ability to do the measurement can also influence the outcome of the correct measurement. For best results it is therefore highly recommended that the test be carried out by the same experienced professional, using the same technique and same calliper. Below is a good indication of where your body fat % should and shouldn’t be: • For woman below 30 years a body fat % of 12- 23% is ideal • For woman between 30 and 50 years a body fat % of 16-23% is ideal • For woman over 50 years a body fat% of 16-25% is ideal. What to do if your body fat% is too high? If you find that your BMI falls in the “overweight” zone or that your fat percentage is too high, the best approach would be to follow a calorie restricted diet together with an exercise program that consists of cardio and weight training, not just cardio. This should be done at least 3 to 5 times a week to help shed those extra kilos.

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