Hydrostatic weighing Irrespective of the location from which they are obtained, the fat cells in humans are composed almost entirely of pure triglycerides with an average density of about 0. Most modern body composition laboratories today use the value of 1. With a well engineered weighing system, body density can be determined with great accuracy by completely submerging a person in water and calculating the volume of the displaced water from the weight of the displaced water.
A correction is made for the buoyancy of air in the lungs and other gases in the body spaces. Whole-body air displacement plethysmography[ edit ] Body composition measurement with whole-body air displacement plethysmography ADP technology Whole-body air displacement plethysmography ADP is a recognised and scientifically validated densitometric method to measure human body fat percentage.
Air-displacement plethysmography offers several advantages over established reference methods, including a quick, comfortable, automated, noninvasive, and safe measurement process, and accommodation of various subject types e. The light is reflected from the underlying muscle and absorbed by the fatileur. The method is safe, noninvasive, rapid and easy to use. Dual energy X-ray absorptiometry Dual energy X-ray absorptiometry, or DXA formerly DEXA , is a newer method for estimating body fat percentage, and determining body composition and bone mineral density.
X-rays of two different energies are used to scan the body, one of which is absorbed more strongly by fat than the other. A computer can subtract one image from the other, and the difference indicates the amount of fat relative to other tissues at each point. A sum over the entire image enables calculation of the overall body composition. Expansions[ edit ] There are several more complicated procedures that more accurately determine body fat percentage. Some, referred to as multicompartment models, can include DXA measurement of bone, plus independent measures of body water using the dilution principle with isotopically labeled water and body volume either by water displacement or air plethysmography.
Various other components may be independently measured, such as total body potassium. In-vivo neutron activation can quantify all the elements of the body and use mathematical relations among the measured elements in the different components of the body fat, water, protein, etc.
Since fat tissue has a lower density than muscles and bones, it is possible to estimate the fat content. This estimate is distorted by the fact that muscles and bones have different densities: Please help improve this section by adding citations to reliable sources.
Unsourced material may be challenged and removed. March Learn how and when to remove this template message The bioelectrical impedance analysis BIA method is a lower-cost from less than one to several hundred US dollars in  but less accurate way to estimate body fat percentage. The general principle behind BIA: The resistance between the conductors will provide a measure of body fat between a pair of electrodes, since the resistance to electricity varies between adipose , muscular and skeletal tissue.
Factors that affect the accuracy and precision of this method include instrumentation, subject factors, technician skill, and the prediction equation formulated to estimate the fat-free mass. Each bare foot may be placed on an electrode, with the current sent up one leg, across the abdomen and down the other leg. For convenience, an instrument which must be stepped on will also measure weight. Alternatively, an electrode may be held in each hand; calculation of fat percentage uses the weight, so that must be measured with scales and entered by the user.
The two methods may give different percentages, without being inconsistent, as they measure fat in different parts of the body. More sophisticated instruments for domestic use are available with electrodes for both feet and hands. There is little scope for technician error as such, but factors such as eating, drinking and exercising must be controlled  since hydration level is an important source of error in determining the flow of the electric current to estimate body fat. The instructions for use of instruments typically recommended not making measurements soon after drinking or eating or exercising, or when dehydrated.
Instruments require details such as sex and age to be entered, and use formulae taking these into account; for example, men and women store fat differently around the abdomen and thigh region. Different BIA analysers may vary. Population-specific equations are available for some instruments, making them more reliable. The term anthropometric refers to measurements made of various parameters of the human body, such as circumferences of various body parts or thicknesses of skinfolds.
Most of these methods are based on a statistical model. Some measurements are selected, and are applied to a population sample. For each individual in the sample, the method's measurements are recorded, and that individual's body density is also recorded, being determined by, for instance, under-water weighing, in combination with a multi-compartment body density model.
From this data, a formula relating the body measurements to density is developed. Because most anthropometric formulas such as the Durnin-Womersley skinfold method,  the Jackson-Pollock skinfold method, and the US Navy circumference method, actually estimate body density, not body fat percentage, the body fat percentage is obtained by applying a second formula, such as the Siri or Brozek described in the above section on density.
Consequently, the body fat percentage calculated from skin folds or other anthropometric methods carries the cumulative error from the application of two separate statistical models. These methods are therefore inferior to a direct measurement of body density and the application of just one formula to estimate body fat percentage. One way to regard these methods is that they trade accuracy for convenience, since it is much more convenient to take a few body measurements than to submerge individuals in water.
The chief problem with all statistically derived formulas is that in order to be widely applicable, they must be based on a broad sample of individuals. Yet, that breadth makes them inherently inaccurate. The ideal statistical estimation method for an individual is based on a sample of similar individuals. For instance, a skinfold based body density formula developed from a sample of male collegiate rowers is likely to be much more accurate for estimating the body density of a male collegiate rower than a method developed using a sample of the general population, because the sample is narrowed down by age, sex, physical fitness level, type of sport, and lifestyle factors.
On the other hand, such a formula is unsuitable for general use. Body Fat Caliper Skinfold methods[ edit ] The skinfold estimation methods are based on a skinfold test, also known as a pinch test, whereby a pinch of skin is precisely measured by calipers at several standardized points on the body to determine the subcutaneous fat layer thickness. Some formulas require as few as three measurements, others as many as seven. The accuracy of these estimates is more dependent on a person's unique body fat distribution than on the number of sites measured.
As well, it is of utmost importance to test in a precise location with a fixed pressure. Although it may not give an accurate reading of real body fat percentage, it is a reliable measure of body composition change over a period of time, provided the test is carried out by the same person with the same technique. Skinfold-based body fat estimation is sensitive to the type of caliper used, and technique.
This method also only measures one type of fat: Two individuals might have nearly identical measurements at all of the skin fold sites, yet differ greatly in their body fat levels due to differences in other body fat deposits such as visceral adipose tissue: Some models partially address this problem by including age as a variable in the statistics and the resulting formula. Older individuals are found to have a lower body density for the same skinfold measurements , which is assumed to signify a higher body fat percentage.
However, older, highly athletic individuals might not fit this assumption, causing the formulas to underestimate their body density. Ultrasound[ edit ] Ultrasound is used extensively to measure tissue structure and has proven to be an accurate technique to measure subcutaneous fat thickness. By making thickness measurements at multiple sites on the body you can calculate the estimated body fat percentage. Ultrasound equipment is expensive, and not cost-effective solely for body fat measurement, but where equipment is available, as in hospitals, the extra cost for the capability to measure body fat is minimal.
Body mass index There also exist formulas for estimating body fat percentage from an individual's weight and girth measurements. For example, the U. Navy circumference method compares abdomen or waist and hips measurements to neck measurement and height and other sites claim to estimate one's body fat percentage by a conversion from the body mass index.
Navy the method is known as the "rope and choke. Marine Corps also rely on the height and circumference method. Females are measured around the hips, waist, and neck. These measurements are then looked up in published tables, with the individual's height as an additional parameter. This method is used because it is a cheap and convenient way to implement a body fat test throughout an entire service. Methods using circumference have little acceptance outside the Department of Defense due to their negative reputation in comparison to other methods.
The method's accuracy becomes an issue when comparing people with different body compositions, those with larger necks artificially generate lower body fat percentage calculations than those with smaller necks. From BMI[ edit ] Body fat can be estimated from body mass index BMI , a person's mass in kilograms divided by the square of the height in meters; if weight is measured in pounds and height in inches, the result can be converted to BMI by multiplying by These formulae are based on work by researchers published in peer-reviewed journals, but their correlation with body fat are only estimates; body fat cannot be deduced accurately from BMI.
Body fat may be estimated from the body mass index by formulae derived by Deurenberg and co-workers. Internal and external cross-validation of the prediction formulas showed that they gave valid estimates of body fat in males and females at all ages.
Other indices may be used; the body adiposity index was said by its developers to give a direct estimate of body fat percentage, but statistical studies found this not to be so.