Remember all those times your were convinced the scale was lying? It turns out you were sort of right. The number on the scale can only tell you so much about your health. It's possible to be a normal weight (or even underweight), but have a high of body fat percentage. And it's also possible to be deemed "overweight," but still be in tip-top shape. The best way to determine if you are at a healthy weight is to use a "variety of tools," including ideal body weight (IBW), body mass index (BMI) and waist circumference, says Kristin Koskinen, RD, of Eat Well, Live Well. So get out your calculator and measuring tape — it's time to crunch some numbers.
Finding Your Ideal Body Weight
Ideal body weight, which takes into account your height and gender, is a weight that's supposed to be optimal for "staving off chronic diseases associated with excess body fat, such as heart disease, type II diabetes and metabolic syndrome," says Julie Upton, M.S., R.D., of Appetite for Health.
For women, you can calculate your IBW, by starting with 100 pounds for the first 5 feet of height, and then adding 5 pounds for each inch of height above 5 feet, or subtracting 2 pounds for each inch under 5 feet. From there, dietitians calculate "a range of plus or minus 10 percent based on frame and natural variation in body composition," says Koskinen.
So if you're 5 feet 5 inches, your IBW would be calculated as 100 + (5 x 5), for a total of 125 pounds. When you add in the plus or minus 10 percent, you get an ideal body weight range of 113-138 pounds.
"The range provides room for variance based on body composition, but doesn't guarantee that someone hitting the upper part of the range is there because of extra muscle mass — it may be extra fat that is excessive for their best health," says Koskinen. Conversely, your weight could be above the "ideal" range, and you may still be healthy if you have a low percentage of body fat to muscle.
What's more, while the ideal body weight equation was created to give you a weight range thought to be associated with lower mortality, the results of a large meta-analysis (basically a study of past studies) suggest that people deemed "overweight" by traditional measures actually have lower mortality rates than those of "normal" weight.
Calculating Body Mass Index
Healthcare professional often use BMI, a number calculated using your height and weight, as a screening tool for certain health conditions. To find your own BMI, divide your weight in pounds by your height in inches squared, and them multiply by 703. (Or you can use this online BMI calculator as a shortcut.) A BMI between 18.5 and 24.9 is considered healthy, while anything lower than that is underweight, and anything over is considered overweight (25.0 – 29.9) or obese (30 and above).
While it's helpful to know your BMI, as the National Institutes of Health points out, the calculation has its limitations — most notably, like IBW, it doesn't distinguish between fat and muscle. So two people could have the same BMI, but very different levels of body fat — and ultimately, it's body fat that matters for your health.
Considering Waist Circumference
According study in the journal Frontiers in Public Health, when clinicians use BMI alone to identify individuals as overweight and obese, about half of patients with excess body fat will be overlooked in the screening. The reason? You could be a normal weight and still be what researchers call "metabolically obese." That means you're not overweight, but you are "overfat," as study authors refer to it.
To get a clearer picture of your health, you'll want to determine your waist circumference. "Muscle doesn't accumulate around the waist, fat does," notes Koskinen. So someone with muscular arms and legs might be "overweight" by BMI standards, but if their waist circumference is below what's considered "high-risk," then they're in the clear.
For women, that high-risk number is 35 inches: If you waist circumference above it, you're more likely to develop heart disease and type 2 diabetes. To accurately measure your middle, place a tape measure just above your hipbones while standing, and measure your waist after letting out a breath.
If it turns out you are "overfat" (normal BMI, but a waist circumference over 35), you can improve your body composition with exercise and a healthy diet. Of course, you'll want to consult with your healthcare provider to get a more more detailed assessment.
- Postgraduate Medical Journal: Malnutrition and Ageing
- FamilyDoctor.org: Healthy Ways to Gain Weight If You’re Underweight
- Centers for Disease Control and Prevention: Body Mass Index: Considerations for Practitioners
- European Heart Journal: Normal Weight Obesity: A Risk Factor for Cardiometabolic Dysregulation and Cardiovascular Mortality
- Centers for Disease Control and Prevention: Losing Weight
- FamilyDoctor.org: Good Health Habits at Age 60 and Beyond
- American Council on Exercise: What Are the Guidelines for Percentage of Body Fat Loss?
- Centers for Disease Control and Prevention: Adult Obesity Facts
- WomensHealth.gov: Overweight, Obesity, and Weight Loss Fact Sheet
- Health.gov: Older Adult Health Facts