Too often we step on the scale and make judgments about our physique based on body weight. If you think about it, body weight says little about your body composition or how healthy you are. A measurement that tells you more is body fat percentage. As the name implies, body fat percentage refers to the amount of fat you have relative to other tissues, including bones, organs, muscles, tendons, ligaments, and water. When you weigh yourself on a standard scale, the reading that lights up on the scale is the weight of all the tissues and organs in your body as well as the fluid they contain.
A Normal Body Weight Doesn’t Necessarily Mean a Person is Fit or Healthy
If you judge health strictly by weight, a 130-pound person who’s 5’6″ would appear to be healthy from a weight perspective, but what if you measured her body fat percentage and it was 35%? No longer would she seem so fit and healthy. As you can see, body composition, how much fat you carry relative to muscle and other tissues tells you more than total weight.
At the other end of the spectrum, a woman who’s 5’6″ and weighs 150 pounds may be in top form if she has a body fat percentage of 20%. Yes, the scale can fool you and it frequently does! The scale is a particularly poor instrument for judging the health and fitness of active women who exercise and do resistance training because muscle is denser than fat. If you were to weigh an equal volume of muscle tissue and fat tissue, the muscle would weigh more.
You’ve heard references to “skinny fat,” referring to people who have a normal body weight but a high body fat percentage. Skinny fat becomes more of a problem with age as critical muscle mass is lost. In older people, age-related loss of muscle mass is referred to as sarcopenia and is a leading cause of disability and loss of functionality in people over 60. It becomes more common with age to fall within a normal weight range and still be at risk for health problems due to sarcopenia, a high ratio of fat to muscle.
BMI Isn’t Reliable Either
Neither total body weight nor BMI is a good judge of health and fitness because BMI only takes into account height and weight, not body composition. It also doesn’t consider age or gender. Unfortunately, most health care professionals still use it to determine whether a person is at high risk for health problems related to being under or overweight. Based on BMI, a person is obese with a BMI over 30, but there’s no lack of male bodybuilders who have a BMI greater than 30 because they’re musclebound. Body fat percentage tells you much more.
So what is a healthy body fat percentage for women? It’s not uncommon for competitive female athletes to have a body fat percentage between 14 and 20%, although it’s difficult to sustain a body fat at the low end of this range year round. Women who exercise and have a high level of fitness might fall in the 20% to 24% range, whereas between 25 and 32% body fat is considered healthy. A body fat percentage above 32% falls into the overweight category. What’s considered healthy becomes more lenient with age. For example, a post-menopausal woman wouldn’t be out-of-range until they have a body fat percentage of 35% or greater.
Just as concerning for women, is having a body fat percentage that’s too low. Most experts agree that the minimum body fat percentage consistent with good health for women is around 12%. Women who drop below this level can develop menstrual irregularities and hormonal changes that jeopardize bone health and fertility. Just as damaging is the type of lifestyle habits that often go along with maintaining such a low body fat percentage – undereating and overtraining.
Measuring Body Fat Percentage
Body fat scales for home use give an estimate of body fat percentage, but they’re not entirely accurate. When you step on the scale, it sends a weak electrical current through your feet, up your legs, to your pelvis and back down the other leg, to measure the amount of water in your body and infer from that the amount of fat. The figure can vary based on your level of hydration when you last ate and time of day. Even dirty feet can throw off the results!
Skin-fold measurements, using calipers, are also not entirely accurate. One study showed caliper measurements underestimate body fat percentage by between 3.2 and 5.6% in women. The most accurate method, dual-energy x-ray absorptiometry or DXA, can measure your body fat percentage to within an accuracy of 2%, but you can’t do it at home. DXA is the same technology used to measure bone density.
Other ways of measuring body fat percentage that’s more accurate than bioelectrical impedance include underwater weighing and a Bod Pod, a method that measures air displacement. Some health clubs and sports medicine clinics offer these technologies. Body fat scales can be helpful for monitoring changes in body fat percentage as long as you measure first thing in the morning before eating and drinking and with an empty bladder, but just don’t count on them for absolute accuracy.
Beyond Body Fat Percentage
Body fat percentage isn’t the only marker for health and fitness. Waist measurement is too. The most dangerous type of abdominal fat is visceral fat, the deep belly fat that shows up as an increase in waist circumference. Research clearly shows that women who have a waist measurement of 35 inches or greater are at higher risk for health problems like heart disease because they have more visceral fat.
The Bottom Line
Total body weight and BMI aren’t the best indicators of health or body composition. Body fat percentage and waist circumference are better measures, but a very low body fat percentage isn’t always healthy. The minimum body fat percentage considered safe for women is around 12%. When you fall below this range, your risk for bone loss and fertility problems arise. Although it’s important to maintain a healthy body fat percentage, don’t be overly obsessed with numbers. If you’re exercising regularly, eating a clean diet and you feel good, those are all good signs.
WebMD. “How Accurate Is Body Mass Index, or BMI?”
Berkeley Wellness. “Body Fat Scales: Step Right Up?”
Res Q Exerc Sport. 2004 Sep;75(3):248-58.
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