BMI & BMR explained

Have you ever been confused about your BMI, Body Mass Index or your BMR, Basal Metabolic Rate? Should you care about such things? These are just two of the many ways we measure our body composition and nutrition intake.

There has been a lot of information floating around regarding body composition and body fat percentages the past few years. I am often asked what a healthy percentage of body fat is and the answer will differ from person to person, but as a rule of thumb it looks something like this.

For an average healthy female, the range is 18 to 30 percent.

For an average healthy male, the range is 10 to 25 percent.

Again, these averages have a number of factors tied to them like height, weight, age and your overall health. To be able to say without a doubt a set percentage is healthy for you specifically really becomes a question for a health care professional.

The Body Mass Index or BMI is a way of measuring your weight in relation to your height. Using BMI to measure for your ideal weight is a bit like asking someone to guess your perfect weight. BMI gives you a very general idea of how you scale in proportion to your height, which is based on averages across many body types. Using BMI is so general, two people can have the same height and weight, but very different body shapes and body fat percentages. For example, some of us are pear shaped, apple shaped and of course, hourglass shaped… you get the idea.

Your body fat percentage is a different and much more accurate way to establish whether you’re at a healthy weight or not. When you measure your body fat, you get a pretty good picture of your body composition. There are five primary methods to measure your body fat. Using calipers to measure skin-fold, air displacement, bioelectrical impedance (which does not measure all areas of body fat making it inaccurate), the underwater tank method and the most accurate, which is a fairly new technology, called DEXA (Dual-energy X-ray Absorptiometry).

Should you be concerned about your BMI and body fat percentage? I think the answer is yes to a degree, but these factors are not an absolute to whether you’re healthy or not. If you want to know your body fat percentage so you can take action to reduce it, then have your measurement done professionally. Keep in mind that body fat percentages can be misleading. If you think you are overweight, the amount of fat you have on your body could be just fine, or perhaps you are carrying hidden fat that can be a risk factor for your overall health. It is important to understand your BMI percentage and use body fat as a reference point, not a perfect indicator of your health and fitness.

Your Basal Metabolic Rate or BMR is a completely different calculation used to define your calorie needs while you are inactive. To get a clear understanding of your resting metabolic rate, it represents the number of calories needed to fuel respiration, cardiovascular circulation, body temperature regulation, brain function, cellular repair and maintain your health.

Understanding your BMR can be helpful when you are trying to gain or lose weight. In simple terms, the factors that define an accurate BMR is the amount of energy expended while at rest in a fasted state for about 12 hours. The non-clinical method to establish a rough guideline for your BMR is done through an equation using age, sex, height and weight. Since these calculations can be confusing to get right, you can find many BMR calculators online to get your ball-park estimate.

What is often not considered by many people dealing with weight issues is it takes about 70 percent of your daily energy needs to support our internal systems such as organs and keep your body in sync including our brain, which needs lots of fuel to run at peak performance. The remaining balance of our daily caloric intakes is used to help digest foods and fuel our movement.

When we over-consume calories that are not needed to fuel our body at rest and cover our energy requirements during exercise, our health and weight suffer. This is especially true when it comes to consuming carbohydrates that easily covert to stored fat. This is why it is important to have a basic understanding of your BMR so you have a general idea of what your body needs when you are and when you’re not being active.

Knowing your BMR can give you a good road map to change your caloric intake proportionately when being active. Again, this is only a guide and there are so many factors that can derail calorie counting and calorie burn, you really need to know your overall physical condition to leverage a BMR effectively. Factors like insulin resistance and metabolic disease, which place your body into a state of chronic glucose dependency, will interfere with your ability to burn calories and fat effectively.

Once you have defined your BMR, do not get too hung-up on the numbers. It is just an estimate on how to approach calorie intake or restriction. As mentioned, a BMR guideline is not an absolute metric to follow and such things as eating fewer carbs and more protein, for example, can change how you metabolize your calories.

Also, calorie counting is not an effective way to lose weight. Managing your carbohydrates, protein and fats while having a good grasp on BMR can be an effective way to help manage your weight. Also keep in mind that muscle burns more calories than fat. The more muscle tone you have will help you burn calories and fat much more effectively.

By using both our BMI, Body Mass Index, and the BMR, Basal Metabolic Rate, as reference tools, we can better help ourselves to manage our calories and body composition.

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Judd Jones is a director for The Hagadone Corporation in Coeur d’Alene.