When you're overweight or have a large stomach, you are more likely to suffer from certain health conditions. It isn't usually cost effective to actually measure the amount of your body fat, so doctors usually use different measurements to estimate it in a general way -- or to determine if you have too much body fat in only your abdominal area. Each type of measurement has its advantages and disadvantages.
BMI vs. Waist-to-Hip Ratio Measurements: The Basics
Body mass index uses your height and weight to estimate if you're overweight, and the waist-to-hip ratio -- or WHR -- uses waist circumference and hip circumference to determine whether you have too much fat around your waist. Each of these indicators can be more effective at indicating risk than the other in some situations, although neither number actually measures body composition or the amount of fat and muscle you have.
The healthy range for BMI is between 18.5 and 24.9; any BMI above this is considered overweight, and any BMI below is considered underweight. If your waist-to-hip ratio is larger than 0.8, you have more of an "apple" shape than a "pear" shape, which can indicate you're carrying too much visceral fat. This fat around your belly can increase your risk for type 2 diabetes and heart disease.
Advantages of BMI
Body mass index is the standard measurement used by most doctors to estimate whether you weigh about the right amount for your height. It's easy to use and takes advantage of measurements the doctor's office is probably already taking, so it doesn't really create extra work for the staff. It doesn't cost anything, while the more accurate ways of actually measuring body fat, such as underwater weighing, require an experienced professional and equipment not typically found in every doctor's office, which makes them quite expensive.
If you've got a higher-than-average risk of having a stroke, you may want to pay more attention to your BMI than to your WHR. BMI is better for estimating the likelihood that you might have a stroke than WHR, according to a study published in Archives of Internal Medicine in 2007. Thus, carrying more weight, in general, may be more likely to increase your risk for stroke than having a larger waistline.
Advantages of Waist-to-Hip Ratio
The type of fat in your belly that surrounds your organs, called visceral fat, is the unhealthiest type of fat. BMI doesn't take into account where the fat you're carrying is located. It can also overestimate fat in people who are very muscular and underestimate it in elderly individuals. While the waist-to-hip ratio still doesn't measure actual body fat levels, it's a good indicator of whether you may have too much visceral fat.
WHR is the preferred obesity measurement for determining overall mortality risk, according to a study published in the European Journal of Clinical Nutrition in 2007. This may be especially true in older individuals, as WHR is a better predictor of mortality in people older than 75, according to another study published in The American Journal of Clinical Nutrition in 2006. BMI is more likely to overestimate mortality risk in this group.
WHR may also be more accurate than BMI for predicting heart disease risk and kidney disease. BMI and WHR are equally useful at predicting diabetes risk in an analysis of 32 different studies published in Epidemiologic Reviews in 2007. WHR may be more accurate for predicting diabetes risk in Caucasians than in Asians, however, according to a review article published in the European Journal of Clinical Nutrition in 2010, although more research is needed to verify these results.
Taking Your Measurements
BMI is your weight in pounds divided by your height in inches, squared, and then multiplied by 703. So if you're 5 feet, 5 inches tall and weigh 130 pounds, your BMI would be [130/(65 x 65)] x 703, or 130 divided by 4225 times 703, which is 21.6. This result is a healthy BMI. Don't worry: If you're not a fan of doing the math, you can find many calculators online that will do it for you and interpret the results.
For waist-to-hip circumference calculations, measure your waist about 1 inch above your belly button to the nearest quarter-inch. Measure a few different places around your hips to find the largest measurement; then divide the waist measurement by the hip measurement. It's best to take the measurements when you aren't dressed, as clothing will increase the measurement and provide a result that isn't as accurate. Regardless of waist-to-hip ratio, it isn't healthy for women to have a waist circumference larger than 35 or for men to have one above 40.