Ideal Body Weight (IBW) vs. BMI: Which One Should You Use?

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The American Journal of Clinical Nutrition recently published a study comparing the use of Ideal Body Weight (IBW) and Body Mass Index (BMI). The results? Well, you will become more open-minded about your choices and alternatives after reading this article.

For those of you who have been following our blog, by now you know that we encourage our readers to ask questions and find out the truth themselves, rather than following blindly!

Let’s Be Clear on Which is Which

Body Mass Index or (BMI) is a person’s weight in kilograms divided by the square of height in meters. A high BMI can be an indicator of high body fatness. BMI can be used to screen for weight categories that may lead to health problems but it is not diagnostic of the body fatness or health of an individual.

Ideal Body Weight (IBW) is a weight that is believed to be maximally healthful for a person, based chiefly on height but modified by factors such as gender, age, build, and degree of muscular development.

Ideal Body Weight (IBW)

In order to measure IBW, “metrics that adjust weight for height are used as estimates of underweight, overweight, and weight-associated health risks and mortality.” Basically, maintaining your ideal body weight is supposed to improve your health and help you live longer.

According to Manfred James Muller,”Throughout the past century, different IBW algorithms have been developed based on the general idea that height defines weight as a linear function.”

We have pursued an ideal weight formula for about a century. Hundreds of formulas and tables have been created. Today, despite years of debate, experts still do not have a definite answer regarding the “best” weight for a person.

Below is a list of the most popular “ideal weight” formulas:

Ideal Body Weight Formulas

Hello Eating Disorder and Broken Bones!

If I were self-conscious and believed in this method of calculating my health and mortality and actually try to reach my IBW, I would be miserable and unhealthy. I would have to starve myself, overexercise, and ultimately develop some kind of eating disorder. According to the most popular IBW formulas, I should weigh anything between 101.1 lbs – 136.7 lbs or 55 kgs – 63 kgs.

That's It Chocolate Bites

Most of us would simply accept these numbers, start extreme dieting, and exercise the living daylights out of ourselves in order to achieve the lowest figure. We then fail to reach the target. Starving our bodies and succumbing to yo-yo dieting can lead to morbid obesity and put you in a worse position than you were in when you started.

Based on my ethnicity, genes, body type, and age, I feel that a goal weight of 132 lbs -143 lbs (60 kg – 65 kg) is attainable and healthy. Maintaining the lower limit of 101.1 lbs – 131 lbs (55 -59 kg) would be dangerous and could deplete my muscle mass to a point where my bone density would lower. It would put me at risk of osteoporosis, a condition where decreased bone strength increases the risk of a broken bone. I would also suffer from decreased metabolic rate. My energy levels and mental acuity would also suffer.

Body Mass Index (BMI)

Today, BMI – a mathematical construct where weight is a quadratic function of height is preferred over other indexes of relative weight. According to Manfred James Muller the popularity of BMI is due to the following arguments in its favour:

  • Adult weight increases proportionally to height squared (and thus is not a linear function of height).
  • BMI (rather than IBW) is a stature-independent measure of weight.
  • BMI has a good correlation with fat mass.

BMI has a better correlation with low mortality and thus a healthy BMI range (rather than one defined by IBW) is associated with low mortality. It is important to remember that a healthy BMI range varies, for example, by age, ethnicity, and chronic diseases.

Why Not Use Both?

So it looks like this post is favouring BMI over IBW, doesn’t it? Well, not quite!

What we know is that IBW and BMI have been used very commonly in clinical practice. There are numerous IBW calculators and BMI calculators for use by professionals and by the average Jane. However, for many years, these two concepts were considered incompatible. In a publication by Courtney Peterson, PhD, MSC, of the Pennington Biomedical Research Center, we see the first effort to merge these two concepts. The study provides “a single, universal, and easy-to-use linear equation to calculate IBW and body weight at any BMI. That equation was validated and had an accuracy of 0.5–0.7% based on NHANES data. The algorithm may provide a useful tool to define target weights and weight-loss goals for health practitioners and the general public.”

The article concluded with the following: “Our linear equation increases the sophistication of IBW equations by replacing them with a single universal equation that calculates both IBW and body weight at any target BMI and height. Therefore, our equation is compatible with BMI and can be applied with the use of mental math or a calculator without the need for an app, which makes it a useful tool for both health practitioners and the general public.”

If you want to know more about the equation, please visit ‘Universal equation for estimating ideal body weight and body weight at any BMI’

Why Not Ditch Them Both?

With the advances of modern bio-medical science, we can’t accept these simple measurements as the standard. IBW and BMI consider body weight and height as easy to measure and the data as widely available. Manfred James Muller explains: “that thinking is against science and ignores current understanding of body composition”.

Forget Body Mass Index

Exit IBW and BMI – Enter Body Composition Analysis (BCA)

Body-composition analysis (BCA), according to some, could be one of the most accurate methods of measuring and assessing health based on the size of the body. A body composition analysis takes into consideration the percentage of fat mass and fat-free mass in your body. You can then determine what percentage is stored fat, how the fat is allocated throughout the body, and how these factors relate to certain health risks such as cardiovascular disease. The test result will classify you in the underweight, normal weight, overweight, or obese category.

Measuring BCA – Hydrostatic Weighing

If you are really hard core, hydrostatic weighing may be something for you. You sit on a chair that is placed on a zeroed-out set of scales before exhaling all the air from your lungs. Your head is then placed underwater. As soon as the scales stabilise, your weight is measured. The result is passed through a series of formulas which, ultimately, produce a body-fat reading versus lean body mass (muscle, bone, and organs).

Healthy body composition refers to the relations between individual body components and between organ and tissue masses (rather than on their individual masses) in the context of age- and sex-specific metabolic and functional traits (e.g., energy expenditure, insulin sensitivity, muscle strength, and physical performance) and health risks. Therefore, healthy body weight is not about a specific value or its range; it is about the value within its physical and functional contexts. – Manfred Muller

More Alternatives

It is time to go beyond IBW and BMI because both measures have substantial weaknesses. Below are some more alternatives to help you figure out if you have a healthy body weight.

Body Adiposity Index

Multiply your hip circumference by your height. Clinical studies are yet to show any proof, but many argue that Body Adiposity Index is more accurate than BMI. This is because the resulting figures are approximate. You may want to use BAI in areas where scales may not be available.

Waist-To-Hip Ratio

The waist-to-hip ratio is another way of calculating how much excess weight you are carrying. It also helps determine susceptibility to a number of health issues, including high blood pressure, heart disease, and diabetes. The waist-to-hip ratio is quite easy to calculate as shown below:

  1. Use a tape measure to take a reading from your natural waist line and the widest part of your hips.
  2. Divide the circumference of your waist by your hip circumference measurement.
  3. Compare your results to the results chart below.

waist-to-hip ratio

Body Fat Measuring

This is the simplest way of calculating your body fat. Skin and fat measurements are taken from the waist, shoulder blade, biceps, and triceps using calipers. The resulting readings are in millimeters and are combined into a single figure. The figure is then compared to a chart that takes the patient’s gender, age, and measurement into consideration to determine the body-fat percentage figure. A high body fat figure means you are at risk of suffering from obesity-related conditions.

Final Note

We are by no means endorsing these methods. We do believe that you should research and keep an open mind. If you are already familiar with some of them please let us know in the comment box below if they helped you in your journey to better health and fitness.
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Ideal body weight or BMI: so, what’s it to be?
Universal equation for estimating ideal body weight and body weight at any BMI
5 Alternatives To Body Mass Index (BMI)
Ideal Weight Calculator
Serious Problems of Ideal Body Weight Formulas
Body Composition Assesment

9 thoughts on “Ideal Body Weight (IBW) vs. BMI: Which One Should You Use?

  1. I reblogged your post. I really like you stated the information and than explained how trying to attain the Body image mass is not reasonable for everyone. Great info for everyone to remember that being healthy is better than a certain size

  2. Good tips on how to spruce yourself up when you have to. I would also remind people that its ok not to feel ok and not have to hide it under all the outside layers. Obviously there are times when you have to dress up, suck it up and grin and bear it. But for the rest of the time, be you, messy hair and all

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