Sometimes the scale can be deceiving…
Your weight is a combination of bones, muscle, organs/tissues, and fat. So the reading when you step on the scale can increase if ANY of those components increase. Because of that fact, yes fact, just using your weight to measure your fitness or health is not as helpful as knowing your body composition, as in, how much body fat and muscle mass you have.
Many studies, such as one in this month's Journal of Cardiology, show that the more fat mass you have, the higher (about 30%) your risk for diabetes, fatty liver, abnormal cholesterol, high blood pressure, and clogged arteries. Conversely, if you have high amounts of lean muscle mass, you can lower your risk for these same diseases by about 20%.
So we know too much body fat is a bad thing, but there is also such a thing as too little body fat. This can cause fatigue, decreased energy levels, intolerance to cold temperature, abnormal hormone levels, weak bones, female infertility, and increased risk for first trimester miscarriages.
So what is a "normal" and healthy body fat percentage? Women need a minimum of 13-17% body fat in order to maintain normal hormonal and reproductive function. A healthy range for women ages 18-39 is about 20-30%, with 22-33% being normal for women ages 40-60. Men tend to need less essential fat so normal ranges are slightly lower, at 8-19% for ages 18-39 and 11-21% for ages 40-60.
How you test your body fat also matters. Body mass index (BMI) only takes into account your height and your total weight, so it will not give you these important body composition details. Old-school calipers used to pinch your arm or belly can give widely varying measurements depending on who is doing the testing and which exact body sites are pinched. Body fat scales and handheld devices using bioelectrical impedance (BIA) are popular but can be notoriously unreliable, with readings changing by 5-10% depending on your hydration status and if you have recently eaten or worked out. Hydrostatic weighing is much more reliable than the above methods but entails full body submersion (think dunk tank without the suspense) and can be slightly off by natural differences in bone density or by not being able to expel all the air out of your lungs while underwater. The Bod Pod capsule uses the same principle with the added benefit that you don't need to get wet at all, but has the same accuracy issues as hydrostatic weighing. None of these methods will be able to give you a body site-specific breakdown of measurements either, including an exact measure of visceral fat, that dangerous deep fat surrounding your organs that really increases your risk for metabolic and cardiac diseases. That's why most researchers use DEXA scans--the "gold standard"--as the most reliable and informative measure of body composition.
Whether you are training to play collegiate or professional sports, want to improve your performance in CrossFit or at the gym, or just want to optimize your health and wellness, knowing your body composition is a crucial baseline and excellent way to track your progress.
Stay healthy my friends.
Dr. Jennifer Miranda
PURE executive health & wellness
The exceptional medicine and experience you deserve.