BMI: Yay or Nay?

If you’ve interacted with the health care system at all as an adult, you’ve probably heard the term “BMI” get thrown around a lot. You may have even experienced a doctor or physician recommending that you lose a certain amount of weight in order to reach the “normal” weight range.

But what even is BMI?

What is BMI?

BMI stands for Body Mass Index and its use as a health assessment tool is extremely prevalent in North America. It is a calculation that uses your height (in meters) and weight (in kilograms):

The calculation will give you a number and that number is used to put you into a category that is associated with predicted changes in level of health risk:

This classification system is used almost without fail when doing patient health assessments because it is cheap and extremely easy to use. Interestingly though, the concept of BMI was created by a mathematician as a means to study populations and determine resource allocation. The creator never intended for it to be used to diagnose people on an individual basis.

Why is BMI used?

1. Associations with health outcomes

Studies have found that the risk for chronic disease and premature death is greater in those that fall in the underweight and obese categories. Some research has also found that a 5% to 10% drop in BMI value is associated with improved health outcomes for heart disease and diabetes.

2. Ease of use

As mentioned before, BMI is indeed a very simple and inexpensive tool. All you need to do is measure someone’s height and weight (or even just use their self-reported measurements). There are even BMI calculators online, which means that even the burden of pulling out a physical calculator is avoided!

What are the issues of BMI?

1. BMI ignores body composition

It’s important to remember that two people can have the same height and weight (and therefore, the same BMI) and have vastly different body compositions. One might be leaner and have more muscle mass, while the other may have a higher body fat percentage.

Unfortunately, the BMI system doesn’t concern itself with these nuances; each kilogram is treated equally even though these variations in fat mass, muscle mass, and bone mass can contribute to drastically different health outcomes.

2. BMI ignores fat distribution

The sites of fat storage on one’s body is associated with varying levels of risk for chronic diseases. Specifically, abdominal fat around the belly area is more associated with increased health risks when compared to excess fat in the thighs and hips. Again, the BMI completely ignores these nuances that matter.

3. BMI is not inclusive

The categories shown above were determined by using a very narrow population type. It is not inclusive and therefore, even less accurate for some groups of people. For instance, research shows that the cut-offs need to be adjusted for those of Asian descent because there is greater risk for heart disease at lower BMIs.

Takeaway: The BMI is not the be-all and end-all of health. It can be a useful metric but only when used in conjunction with other variables.

Stay nourished my friends,

Robena