Assessment of weight and health risk involves using three key measures: Show
Body Mass Index (BMI)BMI is a useful measure of overweight and obesity. It is calculated from your height and weight. BMI is an estimate of body fat and a good gauge of your risk for diseases that can occur with more body fat. The higher your BMI, the higher your risk for certain diseases such as heart disease, high blood pressure, type 2 diabetes, gallstones, breathing problems, and certain cancers. Although BMI can be used for most men and women, it does have some limits:
Use the BMI Calculator or BMI Tables to estimate your body fat. The BMI score means the following:
Waist CircumferenceMeasuring waist circumference helps screen for possible health risks that come with overweight and obesity. If most of your fat is around your waist rather than at your hips, you’re at a higher risk for heart disease and type 2 diabetes. This risk goes up with a waist size that is greater than 35 inches for women or greater than 40 inches for men. To correctly measure your waist, stand and place a tape measure around your middle, just above your hipbones. Measure your waist just after you breathe out. The table Risks of Obesity-Associated Diseases by BMI and Waist Circumference provides you with an idea of whether your BMI combined with your waist circumference increases your risk for developing obesity-associated diseases or conditions. Risk Factors for Health Topics Associated With ObesityAlong with being overweight or obese, the following conditions will put you at greater risk for heart disease and other conditions: Risk Factors
For people who are considered obese (BMI greater than or equal to 30) or those who are overweight (BMI of 25 to 29.9) and have two or more risk factors, it is recommended that you lose weight. Even a small weight loss (between 5 and 10 percent of your current weight) will help lower your risk of developing diseases associated with obesity. People who are overweight, do not have a high waist measurement, and have fewer than two risk factors may need to prevent further weight gain rather than lose weight. Talk to your doctor to see whether you are at an increased risk and whether you should lose weight. Your doctor will evaluate your BMI, waist measurement, and other risk factors for heart disease. The good news is even a small weight loss (between 5 and 10 percent of your current weight) will help lower your risk of developing those diseases. From Calipers to CAT Scans, Ten Ways to Tell Whether a Body Is Fat or LeanWhat’s the best way to determine whether a body is fat or fit? Body fat can be measured in several ways, with each body fat assessment method having pros and cons.
Here is a brief overview of some of the most popular methods for measuring body fat-from basic body measurements to high-tech body scans-along with their strengths and limitations. (Adapted from (1)) Body Mass Index (BMI)Body mass index (BMI) is the ratio of weight to height, calculated as weight (kg)/height (m2), or weight (lb)/height (in2) multiplied by 703. Strengths
Limitations
Waist CircumferenceWaist circumference is the simplest and most common way to measure “abdominal obesity”-the extra fat found around the middle that is an important factor in health, even independent of BMI. It’s the circumference of the abdomen, measured at the natural waist (in between the lowest rib and the top of the hip bone), the umbilicus (belly button), or at the narrowest point of the midsection. Strengths
Limitations
Waist-to-Hip RatioLike the waist circumference, the waist-to-hip ratio (WHR) is also used to measure abdominal obesity. It’s calculated by measuring the waist and the hip (at the widest diameter of the buttocks), and then dividing the waist measurement by the hip measurement. Strengths
Limitations
Skinfold ThicknessIn this method, researchers use a special caliper to measure the thickness of a “pinch” of skin and the fat beneath it in specific areas of the body (the trunk, the thighs, front and back of the upper arm, and under the shoulder blade). Equations are used to predict body fat percentage based on these measurements. Strengths
Limitations
Bioelectric Impedance (BIA)BIA equipment sends a small, imperceptible, safe electric current through the body, measuring the resistance. The current faces more resistance passing through body fat than it does passing through lean body mass and water. Equations are used to estimate body fat percentage and fat-free mass. (1) Strengths
Limitations
Underwater Weighing (Densitometry)Individuals are weighed in air and while submerged in a tank. (1) Researchers use formulas to estimate body volume, body density, and body fat percentage. Fat is more buoyant (less dense) than water, so someone with high body fat will have a lower body density than someone with low body fat. This method is typically only used in a research setting. Strengths
Limitations
Air-Displacement PlethysmographyThis method uses a similar principle to underwater weighing but can be done in the air instead of in water. (1) Individuals sit in a small chamber wearing a bathing suit; one commercial example is the “Bod Pod.” The machine estimates body volume based on air pressure differences between the empty chamber and the occupied chamber. Strengths
Limitations
Dilution Method (Hydrometry)Individuals drink isotope-labeled water and give body fluid samples. Researchers analyze these samples for isotope levels, which are then used to calculate total body water, fat-free body mass, and in turn, body fat mass. (1) Strengths
Limitations
Dual Energy X-ray Absorptiometry (DEXA)X-ray beams pass through different body tissues at different rates. So DEXA uses two low-level X-ray beams to develop estimates of fat-free mass, fat mass, and bone mineral density. (1) DEXA is typically only used for this purpose in research settings. Strengths
Limitations
Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI)These two imaging techniques are now considered to be the most accurate methods for measuring tissue, organ, and whole-body fat mass as well as lean muscle mass and bone mass. (1) CT and MRI scans are typically only used for this purpose in research settings. Strengths
Limitations
References1. Hu F. Measurements of Adiposity and Body Composition. In: Hu F, ed. Obesity Epidemiology. New York City: Oxford University Press, 2008; 53–83. |