Understanding Numbers Part 2: BMI, Body Fat, and Waist-to-Hip Ratio

This is part 2 of a 4-part series designed to help you better understand some of the tests that you get each year at your physical with your doctor. These numbers are important to your health, and understanding what they mean can help you to improve not only the numbers themselves, but your overall health and wellness.

Body Mass Index

The next measurement that your doctor may take is your BMI. BMI stands for “Body Mass Index”, and it is a measurement for relating your body weight to your height. The reason that doctors tend to use this, is because it’s quick and easy to calculate. The formula for BMI is weight in kg divided by height in meters squared. The number you get will put you in one of four categories:

Age Low Normal High Very High
Males 20-39 <8.0 8.0-19.9 20.0-24.9 25.0+
40-59 <11.0 11.0-21.9 22.0-27.9 28.0+
60-79 <13.0 13.0-24.9 25.0-29.9 30.0+
Females 20-39 <21.0 21.0-32.9 33.0-38.9 39.0+
40-59 <23.0 23.0-33.9 34.0-39.9 40.0+
60-79 <24 24.0-35.9 36.0-41.9 42.0+

The issue with BMI is that it does not take into account muscle mass. This means that it may not be the best indicator of your body composition. Having a high BMI does not always mean you are overweight, if you are extremely muscular. This is why body fat percentage is a much better measure of overall body composition. For example, an extremely lean bodybuilder with a ton of muscle will have a low body fat percentage, but might fall into the high category of BMI.


Body Fat Percentage

So why don’t doctors measure body fat? It’s a little more complicated! There are different ways of measuring body fat, including:

  • Skinfolds (manually using calipers)
  • Bod Pod
  • Hydrostatic Weighing
  • Bioelectrical Impedance (InBody Scale, handheld device)
  • DEXA (Dual-Energy X-Ray Absorptiometry) – this is considered the “gold standard”!
  • 3D Body Scan
  • Air-Displacement Plethysmography

The different ways of measuring all have pros and cons, but if you just want a baseline reading, you’d be fine with using a handheld device or having it done manually at your gym. The other options are not as readily available, and can be very expensive! I had to do hydrostatic weighing at school and let me tell you, it was NOT fun (hydrostatic weighing is when you are lowered into a huge tub of water and they measure the water displacement. You have to release ALL the air from your body and hold your breath. Like I said-not fun).

Body fat norms look like this:

797386f764539c0a8b3c4df1cd76a800If you’re interested in knowing your body fat, see if there’s someone at your gym who can take it for you! Or, at the very least, see if they  have a handheld device or scale that can measure it. I’m old school, and I actually like using the calipers and doing the  skinfold method! I even have my own set of calipers at home!


Waist-to-Hip Ratio

Another thing that your doctor may measure is your waist-to-hip ratio and your waist circumference. This is a fairly accurate way of measuring your risk for various diseases. When you carry most of your body fat above the waist, in the abdominal area, it puts you at a higher risk for diseases, including:

  • Diabetes
  • High Cholesterol
  • Hypertension
  • Heart Disease

Fat that is carried around the hips and thighs does not carry the same risk for disease as does abdominal fat. The waist-to-hip ratio is calculated by dividing waist inches by hip inches.

Waist-to-Hip Ratio Males Females
High Risk > 0.9 > 0.85

Since waist circumference is a good way to screen for possible health risks, it’s a good idea to keep track of your waist measurement. Your risk of disease goes up with a waist size greater than 35″ for females and greater than 40″ for males.

Waist Circumference Males Females
High Risk > 40” > 35”

Managing Body Composition

Lowering your BMI, body fat percentage, and waist-to-hip ratio is possible!

  • Eat a healthy, well-balanced diet. Increase your fiber intake to help regulate your body systems, stay in a caloric deficit, keep healthy snacks on hand, and drink lots of water throughout the day
  • Exercise regularly. Aerobic exercise is best for lowering BMI, while strength training can be used for lowering body fat. Be sure to include both types of training for beset results. Try brisk walking, running, dancing, swimming, step climbing, rowing, lifting weights, exercises classes, etc.
  • Keep track on your own using a BMI calculator and getting your body fat measured regularly. Here is a good BMI calculator than you can use on your own. Also be sure to take your waist and hip measurements regularly, and see if you can get a monthly measure of your body fat at your gym!

Knowing your body composition is important for your overall health. It’s even more important if your goal is fat loss! While it’s nice to get your BMI reading once a year at the doctor, it’s also a good idea to keep track of things yourself. Take your  measurements, use progress photos, and calculate your BMI on a regular basis. Always talk with your doctor if you have concerns about your body composition. And if you’re interested in fat loss, shoot me an email and see if my online coaching is right for you!

Part 3: Blood Glucose coming is coming up next!

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