understanding

body fat analysis

understanding

body fat analysis

Tanita Corporation of America Inc. 847 640 9241 phone2625 South Clearbrook Drive 847 640 9261 fax Arlington Heights, Illinois 60005 www.tanita.com

©2000 Tanita Corporation of America Inc. All rights reserved.(TBF-B7.3) 10M/4-00 HDI. Printed in USA.

Tanita, the world leader in precision electronic scales,is committed to the research and development ofproducts that help people achieve a healthier life.In 1992, the company introduced the world’s first integrated body fat monitor and scale for professionaluse based on BIA (bioelectrical impedance analysis).Since then, Tanita has adapted this technology for the consumer market.

For more information on Tanita’s complete productoffering, including a full line of professional andhome-use body fat monitors, or answers to technicalquestions, call toll free 1-800-TANITA-8.

Who is Tanita?

Version 2.1

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Methods Cover (V2.1)•final 4/10/00 11:25 AM Page 1

25%Bibliography

Bioelectrical impedance analysisin body composition measurement:National Institutes of HealthTechnology AssessmentConference Statement. (1996).American Journal of ClinicalNutrition.

Clinical Guidelines on theIdentification, Evaluation,and Treatment of Overweight and Obesity in Adults. (1998).National Heart, Lung, and BloodInstitute and National Institute of Diabetes and Digestive and Kidney Diseases, NationalInstitutes of Health.

Eating and Body Image.(Dec. 1995, Vol.III, #4). HarvardWomen’s Health Watch.

Exercise, Obesity and WeightControl. The Bariatrician.(Winter 1995).

Futrex Technical Literature.

Heymsfield, S.B. (1998).Lecture on Body Composition.Obesity Research Center,St. Luke’s-Roosevelt Hospital,Columbia University College ofPhysicians and Surgeons, NY, NY.

Heyward, V.H. (Sept. 1996).Evaluation of Body Composition.Sports Medicine. Adis Intl. Ltd.

Heyward, V.H. and Stolarczyk, L.M.(1996). Applied BodyComposition Assessment.Human Kinetics.

Jebb, Susan A. (1998).Measuring Body Compositionfrom the Laboratory to the Clinic.Clinical Obesity (18-49).Blackwelll Science Ltd.

Kushner, Kunigk, Alspaugh,Leitch, Schoeller. (Aug. 1990).Validation of BIA as a measure-ment of change in body compo-sition in obesity. AmericanJournal of Clinical Nutrition.

Lohman, T.C. (1992,Monograph #3). Advances inBody Composition Assessment.Current Issues in ExerciseScience. Human Kinetics.

Lukaski, H.C. (1987). Methods for the assessment of humanbody composition: traditional and new. American Journal ofClinical Nutrition.

Margolis, S., Cheskin, L.J. (1997,1998). Weight Control. JohnsHopkins White Papers. The JohnsHopkins Medical Institutions.

Middle-Age Spread. (Aug. 1995,Vol.II, #12). Harvard Women’sHealth Watch.

Nieman, D.C. (1986). Fitness and Sports Medicine: A Health-Related Approach. 3rd Edition.Mayfield Publishing Company.

Nieman, D.C. (1998). TheExercise-Health Connection.Human Kinetics.

Nunez, C., Gallagher, D., Visser,M., Pi-Sunyer, F.X., Wang, Z.,Heymsfield, S.B. (1997).Bioimpedance analysis: evalua-tion of leg-to-leg system basedon pressure contact footpadelectrodes. Medicine and Sciencein Sports and Exercise. AmericanCollege of Sports Medicine.

Pi-Sunyer, F.X. (Oct.1993,Vol. 119,#7). Medical Hazards of Obesity.Annals of Internal Medicine.American College of Physicians.

Tanita Technical Literature.

Tsui, E.Y.L., Gao, X.J., Zinman, B.(Mar. 1998). BioelectricalImpedance Analysis (BIA) Using Bipolar Foot Electrodes in Assessment of BodyComposition in Type 2 DiabetesMellitus. Diabetic Medicine.

Williams, D.P., Going, S.B.,Milliken, L.A., Hall, M.C.,Lohman, T.G. (1995). Practicaltechniques for assessing bodycomposition in middle-aged andolder adults. Medicine andScience in Sports and Exercise.American College of SportsMedicine.

Yet Another Word on Weight.(Aug. 1998, Vol. V, #12).Harvard Women’s Health Watch.

An Introduction 01

Body Composition 04

Reference Models 06

Basic Terms 08

Determining Obesity 10

Calipers 12

Dunk Tank 14

BIA 16

Tanita BIA 18

NIR 20

DEXA 21

Other Methods 22

In Conclusion 23

A Message for Women 24

Bibliography 25

Methods Cover (V2.1)•final 4/10/00 11:25 AM Page 3

Recently, a student askedme what benefits I getfrom my personal exerciseprogram besides puttingin miles on my bicycle. . . I was tempted to say that exercising outside in the fresh air always makes me feel good, but instead, I replied: In addition to the cardio-vascular benefits I’ve gained in the last sixmonths, I’ve lost eight pounds of fat—I’vereduced my body fat level from 18% of mytotal weight to 14%.

This is the kind of definitive statement youcan make after adding body composition analysisto your exercise and diet program as I have. Ifweight loss or maintenance is your goal, accuratebody fat testing is a terrific and more precise wayto monitor your progress while you’re makingslow but gradual gains. It can be a valuabletool—if you understand it.

This may sound like a contradiction, but youcan be overfat but not overweight; or overweightand not overfat. And when you exercise and dietproperly, you can lose fat without changingyour weight measurement on a scale. Withstrength training or intense aerobic exercise,you can actually gain a few pounds of musclewhile at the same time losing pounds of fat.Most individuals never know this kind of infor-mation because they simply measure weight. I believe that the more information andbiofeedback you have on improvements toyour health and fitness, the more likely you are to stay motivated toward your goals.

01%An Introduction

Everyone needs some body fat and there arerecommended healthy ranges. The ranges formen and women are different because womenare anatomically designed to have about 5%more fat than men of equal fitness.

For both sexes, however, being severelyoverfat or obese can lead to health problems.Obesity is linked to increased risk of diabetes,hypertension, heart disease, stroke, certain cancers, and other debilitating conditions.

If you’re an athlete carrying excess pounds,it’s going to slow you down. But excessive thin-ness can also lead to trouble. While a lean bodymay improve your appearance, strength andspeed, many athletes lower their body fat levelsto such an extreme that they become suscepti-ble to illness. Many athletes that I have workedwith tell me that when they drop below a certain weight and percent body fat they oftenexperience chronic fatigue. Female athletes facean additional problem in that too low a per-centage of body fat (12% or under) can disrupttheir menstrual cycles. So remember, thethinnest and leanest athletes are not alwaysthe strongest. The body needs an adequateamount of fat to be healthy and to use as anenergy source during hard exercise.

When participating in any exercise and diet program you probably know that exerciseincreases metabolism or your body’s ability to burn calories for energy. Weight control is a question of balancing how much food we eatagainst how much energy we expend; and weightloss requires taking in fewer calories and burningoff even more. Dieting alone slows down yourmetabolism, while eating the right foods plus a program of exercise will help you burn offcalories—even when you’re resting.

02%

See recommendedBody Fat Rangeschart on page 11and the Message

for Women onpage 24

As measuring body fat becomes easier andcheaper, and the results of tests more accurate,naturally more people want to know their meas-urements. And, as I have successfully learned,keeping tabs on my body composition can be an important index of my health and state of fit-ness. Personally, I measure my weight and bodyfat twice a week, and use these measurementsin addition to my training mileage as tools tohelp me reach and maintain my fitness goals.

Before you put yourself to the test, under-stand the principles of body fat testing. Thereis more than one way to measure body fat, andeach method has its strengths and weaknesses.Choose one that feels right for you and, moreimportantly, one that you can use on a regularbasis. While conclusions on the best test forbody composition may differ, remember that it is more important to use the same one—consistently—over time.

Edmund R. Burke, Ph.D.

Professor and Director of the Exercise Science Program

University of Colorado at Colorado Springs

Dr. Burke is the author of “Getting in Shape: Programs for Men and

Women” and the “Complete Home Fitness Handbook”; as well as a

regular contributor to numerous scientific journals and publications,

including “Bicycling Magazine” and “Nutritional Science News.”

Dr. Burke’s research interests include sports nutrition, cycling

performance, fitness and adaptations to training. Personally, he enjoys

cycling and hiking and is an experienced international competitor.

He is a Fellow of the American College of Sports Medicine and

a Certified Strength and Conditioning Specialist (CSCS).

03%

Scientists have beenstudying body compositionsince the beginning of the20th century, but researchhas increased dramaticallyin the last 25 years asmethods for measuringand analyzing the bodyhave grown in accuracy. There is growing evidence that clearly linksbody composition with health risks and thedevelopment of certain diseases. New researchindicates that fat loss, not weight loss, canextend human longevity.

Adding further to the acceptance of thispractice is the importance of body compositionin athletic performance and its move frombeing a laboratory-only procedure to one usedin ordinary medical practice and now healthclubs or at home. By measuring body composi-tion, a person’s health status can be more accu-rately assessed and the effects of both dietaryand physical activity programs better directed.

Most people don’t realize that there is onlyone “direct” method of measuring body com-position that is close to 100% accurate, andthat is an autopsy—performed Post Mortem.All other current methods for measuring bodycomposition rely on “indirect” measurementtechniques and are called In Vivo methods—meaning they are performed on a living body.

Body Composition04%

In Vivo methods give estimates of percentage ofbody fat, fat-free mass, muscle, bone density,hydration, or other body components. Eachmethod uses one or more measurable body com-ponent (such as skinfold thickness, resistance,etc.) to make educated predictions about theother components. These predictions are basedon years of research that define statistical rela-tionships between different body components.

According to the National Institutes ofHealth, no trial data exist to indicate that onemethod of measuring body fat is better thanany other for following overweight and obesepatients during treatment. Good results dependupon accurately taken measurements and anadequate, scientifically derived database. Everymeasurement method has strengths as well asdefined sources of error. Most research studiesemploy several methods used in combination.

Body composition equipment manufacturersshould have scientific studies available to sup-port accuracy claims, but often companies failto explain the problems encountered in day-to-day use outside of the controlled environment ofa research lab. Tanita feels it is very importantfor people to fully understand the benefits—and limitations—of body composition analysis.This information will enable people to makebetter decisions about which method is the bestor most appropriate for their particular needs.

05%

Body Composition ModelsThe more traditional methods are based on atwo-compartment model that simply dividesthe body into fat and fat-free mass.Hydrodensitometry (underwater weighing) isbased on the two-compartment model.

Newer, more sophisticated techniques, suchas DEXA (dual energy x-ray absorptiometry),measure the body as multiple compartments.This approach improves the accuracy of thecalculation for determining the real density offat-free mass.

There are two basic body-composition models:the two-compartment model—fat-free mass and fat; and thefour-compartment model—bone/mineral, protein, water, and fat.

Reference Models Often referred to as “gold standards,” these areclinical techniques that have been validatedthrough repeated scientific studies and againstwhich other clinical and field method results areevaluated. The two main reference models todayare Hydrodensitometry and DEXA.

06%

Fat

Fat-Free Mass

Fat

Water

Protein

Bone/Mineral

Prediction EquationsIn Vivo methods use equations to predict percent-age of body fat, fat-free mass, muscle, hydration,etc. Using a form of statistics known as multipleregression analysis, this allows an unmeasurablecomponent, such as body fat, to be predicted fromone or more measured variable, where studieshave proved there is a correlation. For example,calipers use external skinfold measurements (a method that estimates fat found just under theskin) to calculate total body fat. BIA measures the body’s impedance (resistance) to an electricalsignal to estimate total body fat.

Equations can be population-specific (devel-oped for specific types of people, includingsuch categories as gender, age, ethnicity, fitnesslevel, disease, etc.) or generalized to cover awide range of people types. A given equation isvalidated according to how well the resultsmatch the results of the reference method.

It is important to note that results of refer-ence methods themselves do not agree 100 per-cent. Therefore, when comparing differentmethods or products, you should considerwhich reference method was used and theappropriateness of both the method and partic-ular product for the body type being analyzed.

07%

refers to the total weight of the body includingbones, muscle, fat, water, etc.

is defined as a body weight that exceeds theacceptable weight for a particular person, basedon individual height and/or frame size. Standardsare usually determined solely on the basis ofpopulation averages that can and do changeover time. Standards may also vary with genderand ethnicity. An overweight person does notnecessarily have too much fat nor increasedhealth risks if the excess weight is due to anabove-average amount of muscle.

is the condition where the individual has anexcessive amount of body fat. Over 30 specificdiseases have been linked to obesity.

is the percentage of total body weight that is fat(see page 11 for recommended body fat ranges).

means the actual fat mass (in pounds or kilos)in the body.

functions as insulation, protection and energyreserve. When the percentage is too high, fatincreases a person’s risk of high blood pressure,elevated cholesterol, diabetes, heart disease,and some forms of cancer. It can also interferewith the immune system, prevent heat loss,stress the musculoskeletal system, cause sleepproblems, and may affect self-esteem.

is the rate at which the body burns calories tomaintain normal body functions while at rest.It is affected by the amount of muscle youhave. Body weight remains constant when youburn up the same number of calories that youeat. A 3,500 calorie difference between dietaryintake and energy expenditure is necessary togain or lose one pound of fat. Weight loss bydiet alone may result in a loss of muscle, andthis will slow your metabolic rate, making itmore difficult to keep the weight off. Exercise,

Basic Terms08%

Weight

Overweight

Obesity(Overfat)

PercentageBody Fat

Fat Mass

Body Fat

Basal Metabolic

Rate (BMR)

however, increases your metabolic rate forhours even after exercise, and can increase theamount of muscle you have.

Weight measurement alone cannot alwaysaccurately determine the body fat status of aperson because it does not differentiate betweenthe fat-free mass and fat mass in the body. Therelationship between three categories of bodyweight and body fat can be described accordingto five different people categories.

1 Athletic or muscular body types (bodybuilders) who havenormal or low body fat even though they are overweightaccording to standard charts.

2 Lean, thin or linear body types with low amounts of fat-freemass (endurance athletes) who can be underweight according to the weight charts and extremely low in body fat yet physically very healthy.

3 People of average weight and average body fat mass.

4 Big, heavy and soft body types who are overweight and obese from large amounts of fat mass and body weight.

5 People (often the elderly) who have too much fat mass and are obese but not overweight due to inactive and sedentary lifestyles.

09%

Body Fat

Weight

Lean

Over

Aver

age

Unde

r

Medium Obese

2Underweight

and leane.g.: runners

3Average,

healthy weightand body fat

4Overweight

andobese

5Obese not

overweight, e.g.: inactive elderly

1Overweightnot obese,

e.g.: bodybuilders

WeightVersus

Body Fat

Height-Weight Tables were originally devel-oped by insurance companies to establish rec-ommended weight ranges for men and women.The “desirable” weights were those associatedwith the lowest mortality among large popula-tion studies of insured people. Unfortunately,these studies do not accurately represent across-section of the entire American population.

Body Mass Index (BMI) is a simple calculationthat determines height to weight ratio. BMI isobtained by multiplying weight in pounds by700 and dividing the result by the square ofheight in inches. This index correlates a person’sphysical stature with mortality ratios based onactuarial studies. According to NationalInstitutes of Health (NIH) and World HealthOrganization (WHO) guidelines, overweight isdefined as a BMI of 25–29.9, and obesity as aBMI equal to or greater than 30. A person witha BMI of 30 is about 30 lbs. overweight/overfat.A BMI of 18 or lower indicates that a person isunderweight/underfat.

While BMI is widely accepted, it can bemisleading. Current guidelines do not differen-tiate for gender, ethnicity or age, and do notdistinguish obesity or leanness for individualswho are extremely muscular. It is, however,more precise than height/weight tables andallows comparisons of population groups.Studies have confirmed that obesity-relatedhealth risks start in the BMI range of 25–30.

Waist Measurement Waist size is an additional, independent riskfactor and can be used in conjunction with anyother method. It reflects growing evidence thatexcess visceral fat—surrounding the abdomi-nal organs—on its own increases the chance ofheart disease or diabetes.

Determining Obesity10%

Research indicates that visceral fat (waistsize) is more important in the disease processthan subcutaneous fat which is just under theskin (“love handles,” “pinchable inches”).Abdominal fat cells appear to produce certaincompounds that may influence cholesterol andglucose metabolism. In men, a waist size of ≥ 40" and in women ≥ 35" is an indication ofincreased health risk.

Body Fat Ranges for Standard Adults1,2

11%

20–39

40–59

60–79

Healthy Overfat ObeseUnderfat

Based on NIH/WHO BMI Guidelines. As reported by Gallagher, et al., at NY Obesity Research Center. To determine the percentage of body fat that is appropriate for your body, consult your physician.

10%0% 20% 30% 40%

20–39

40–59

60–79

Female

Age

Male

Age

1.

2.

Android or“apple-shaped”obese peopleare more vulnerable todisease thanthose who are gynoid or“pear-shaped.”

Anthropometry (Skinfold Measurements)Using hand-held calipers that exert a standardpressure, the skinfold thickness is measured at various body locations (3–7 test sites arecommon). Then a calculation is used to derivea body fat percentage based on the sum of themeasurements. Different prediction equationsare needed for children and specific ethnicgroups (over 3,500 equations have been vali-dated). This approach usually uses underwaterweighing as a reference method (see page 14).The caliper method is based upon the assump-tion that the thickness of the subcutaneous fat(found just under the skin) reflects a constantproportion of the total body fat (contained inthe body cavities), and that the sites selected formeasurement represent the average thickness ofthe subcutaneous fat.

Skinfold measurements are made by grasp-ing the skin and underlying tissue, shaking itto exclude any muscle and pinching it betweenthe jaws of the caliper. Duplicate readings areoften made at each site to improve the accuracyand reproducibility of the measurements. Oftento save time in large population studies, a singleskinfold site measurement is made to reducethe time involved. Such a test should be usedonly for a rough estimate of obesity.

Calipers12%

This approach isbased upon theassumption thatthe thickness of

fat found justunder the skin

reflects a constant proportion of the

total body fat.

Generally speaking, skinfold measurementsare easy to do, inexpensive and the method isportable. Overall, results can be very subjectiveas precision ultimately depends on the skill ofthe technician and the site measured. Thequality of the calipers is also a factor; theyshould be accurately calibrated and have a con-stant specified pressure. Inexpensive modelssold for home use are usually less accurate thanthose used by an accredited caliper technician.The more obese the subject, the more difficultto “pinch” the skinfold correctly, requiring evenmore skill to obtain an accurate measurement.

13%

Grasp the skin,shake it,

and pinch itbetween the jaws

of a caliper.

Hydrodensitometry (Underwater Weighing)This method measures whole body density bydetermining body volume. There is a variety of equipment available to do underwaterweighing ranging in sophistication from thestandard stainless steel tank with a chair or cotmounted on underwater scales, to a chair andscale suspended from a diving board over a poolor hot tub.

This technique first requires weighing aperson outside the tank, then immersing themtotally in water and weighing them again. The densities of bone and muscles are higherthan water, and fat is less dense than water. So a person with more bone and muscle willweigh more in water than a person with lessbone and muscle, meaning they have a higherbody density and lower percentage of body fat.

The Dunk Tank14%

A person withmore bone andmuscle will weighmore in water,meaning theyhave a higherbody density andlower percentageof body fat.

The underlyingassumption with

this method is that densities of

fat mass and fat-free mass are constant.

The volume of the body is calculated and theindividual’s body density is determined byusing standard formulas. Then Body FatPercentage is calculated from body densityusing standard equations (either Siri or Brozek).

The underlying assumption with this methodis that densities of fat mass and fat-free mass areconstant. However, underwater weighing maynot be the appropriate gold standard for every-one. For example, athletes tend to have denserbones and muscles than non-athletes, whichmay lead to an underestimation of body fat percentage. While the body fat of elderlypatients suffering from osteoporosis may beoverestimated. To date, specific equations havenot been developed to accommodate these different population groups.

An important consideration in this methodis the amount of air left in a person’s lungsafter breathing out. This residual lung volumecan be estimated or measured, but it is estab-lished that a direct measure is desirable and itshould be taken in the tank whenever possible.Another consideration is that the water in thetank must be completely still; there can be nowind or movement.

Although this method has long been con-sidered the laboratory “gold standard,” manypeople find it difficult, cumbersome, anduncomfortable, and others are afraid of totalsubmersion or cannot expel all the air in theirlungs. Clinical studies often require subjects tobe measured three to five times and an averagetaken of the results.

15%

Bioelectrical Impedance Body impedance is measured when a small, safeelectrical signal is passed through the body, carriedby water and fluids. Impedance is greatest in fattissue, which contains only 10–20% water, whilefat-free mass, which contains 70–75% water,allows the signal to pass much more easily. Byusing the impedance measurements along witha person’s height, weight, and body type (gender,age, fitness level), it is possible to calculate the per-centage of body fat, fat-free mass, hydration level,and other body composition values. ConventionalBIA normally uses underwater weighing as itsmethod of reference (see pages 7 and 14).

Using BIA to estimate a person’s body fatassumes that the body is within normal hydra-tion ranges. When a person is dehydrated, theamount of fat tissue can be overestimated.Factors that can affect hydration include notdrinking enough fluids, drinking too much caf-feine or alcohol, exercising or eating just beforemeasuring, certain prescription drugs or diuret-ics, illness, or a woman’s menstrual cycle.Measuring under consistent conditions (properhydration and same time of day) will yield bestresults with this method.

Because BIA can be affected by body hydra-tion, many professionals may use this methodas a means of tracking the hydration status oftheir patients. This is especially important forathletes who are training or performing, as wellas for the chronically ill.

In the traditional BIA method, a person lies on a cot and spot electrodes are placed on thehands and bare feet. Electrolyte gel is appliedfirst, and then a current of 50 kHz is introduced.BIA has emerged as a promising technique

BIA16%

This method usesan impedance

reading along witha person’s height,weight, and bodytype to calculate

the percentage ofbody fat.

because of its simplicity, low cost, highreproducibility and non-invasiveness. BIA predic-tion equations can be either generalized or pop-ulation-specific, allowing this method to bepotentially very accurate. Selecting the appropri-ate equation is important in determining thequality of the results. To minimize variablescaused by a person’s hydration level,measurements should always betaken under constant and con-trolled conditions.

For clinical purposes, scien-tists are developing a multi-fre-quency BIA method that mayfurther improve the method’sability to predict a person’shydration level. New segmen-tal BIA equipment that usesmore electrodesmay lead to moreprecise measure-ments of specificparts of the body.

17%

Spot electrodes are placed on thehands and bare feet. Electrolyte gel is appliedfirst, and then acurrent of 50 kHzis introduced.

Tanita has developed a simplified version of BIAthat uses leg-to-leg bioimpedance analysis. Inthis system, two footpad electrodes (pressurecontact) are incorporated into the platform of aprecision electronic scale. A person’s measure-ments are taken while in a standing positionwith the electrodes in contact with bare feet.The body fat monitor/analyzer automaticallymeasures weight and and then impedance.Computer software (a microprocessor) imbed-ded in the product uses the measured imped-ance, the subject’s gender, height, fitness level,and in some cases age, (which have been pre-programmed), and the weight to determinebody fat percentage based on equation formulas.Tanita’s reference method is DEXA (see page 21).

Tanita BIA18%

Tanita’s footpaddesign sends a safe,low level electricalsignal through thebody. As easy asstepping on a traditional scale,it measures weightand body fat percentage within 30 seconds.

Through multiple regression analysis, Tanita hasderived standard formulas to determine body fatpercentage. Tanita’s equations are generalized forstandard adults, athletes, and children.

The Tanita method has all the advantagesof traditional BIA as well as greater ease of use,speed, and portability. Professional versions ofthe product can be found in hospitals, healthclubs, and research labs and include computerprintouts of comprehensive data such as BMI,fat percent, fat weight, total body water, fat-freemass, and BMR. The concept has been adaptedfor use as an affordable home monitoringdevice. Now ordinary people along with fitnessenthusiasts and patients with health risks canmeasure body fat as part of a regular healthylifestyle. The same variables apply with regardto hydration levels, and measuring should bedone under consistent conditions.

19%

A person’s measurements are taken while

in a standing position with

the electrodes in contact with

bare feet

Near-infrared Interactance A fiber optic probe is connected to a digitalanalyzer that indirectly measures the tissuecomposition (fat and water) at various sites onthe body. This method is based on studies thatshow optical densities are linearly related tosubcutaneous and total body fat. The biceps isthe most often used single site for estimatingbody fat using the NIR method. The NIR lightpenetrates the tissues and is reflected off thebone back to the detector. The NIR data isentered into a prediction equation with the per-son’s height, weight, frame size, and level ofactivity to estimate the percent body fat.

This method has become popular outside of the laboratory because it is simple, fast, noninvasive, and the equipment is relativelyinexpensive. However, the amount of pressureapplied to the fibre optic probe during measure-ment may affect the values of optical densities,and skin color and hydration level may bepotential sources of error. To date, studies con-ducted with this method have produced mixedresults; a high degree of error has occurred with

very lean and very obese people; and thevalidity of a single-site measurement atthe biceps is questionable. Numeroussources report that more research is

needed to substantiate the validity, accuracy and applic-ability of this method.

NIR 20%

Illustration is based onthe Futrex-5000/XL

This method isbased on studiesthat show optical

densities are linearly related tosubcutaneous and

total body fat.

c

Dual Energy X-ray Absorptiometry A relatively new technology that is very accurateand precise, DEXA is based on a three-compart-ment model that divides the body into total bodymineral, fat-free soft (lean) mass, and fat tissuemass. This technique is based on the assump-tion that bone mineral content is directly pro-portional to the amount of photon energyabsorbed by the bone being studied.

DEXA uses a whole body scanner that hastwo low-dose x-rays at different sources thatread bone and soft tissue mass simultaneously.The sources are mounted beneath a table witha detector overhead. The scanner passes acrossa person’s reclining body with data collected at0.5 cm intervals. A scan takes between 10–20minutes. It is safe and noninvasive with littleburden to the individual, although a personmust lie still throughout the procedure.

DEXA is fast becoming the new “gold stan-dard” because it provides a higher degree of pre-cision in only one measurement and has theability to show exactly where fat is distributedthroughout the body. It is very reliable and itsresults extremely repeatable; in addition, themethod is safe and presents little burden to thesubject. Although this method is not as accuratein measuring the extremely obese and the costof equipment is high, DEXA is quickly movingfrom the laboratory setting into clinical studies.

21%DEXA

This techniqueassumes that bone mineral

content is directlyproportional to the amount of photon energy

absorbed.

Magnetic Resonance Imaging (MRI)An x-ray based method in which a magneticfield “excites” water and fat molecules in thebody, producing a measurable signal. A personlies within the magnet as a computer scans thebody. High-quality images show the amount offat and where it is distributed.

MRI takes about 30 minutes and is very safeas it uses no ionizing radiation, but use is limiteddue to the high cost of equipment and analysis.

Total Body Electrical Conductivity (TOBEC)This method is based on lean tissue being abetter conductor of electricity than fat. A personlies in a cylinder that generates a very weakelectromagnetic field. The strength of the fielddepends on the electrolytes found in the person’sbody water. In about 10 seconds, TOBEC makes10 conductivity readings that estimate leanbody mass. Although very accurate, its use islimited due to the high cost of the equipment.

Computed Tomography (CT)CT produces cross-sectional scans of the body.An x-ray tube sends a beam of photons towarda detector. As the beam rotates around a person,data is collected, stored, and applied to complexalgorithms to build images that determine bodycomposition. CT is particularly useful in givinga ratio of intra-abdominal fat to extra-abdominalfat. It is noninvasive, but potential is limited byexposure to radiation and high equipment cost.

BOD POD® (Air Displacement)Based on the same principle as underwaterweighing, the BOD POD uses computerizedsensors to measure how much air is displacedwhile a person sits for 20 seconds in a capsule.It uses a calculation to determine body density,then estimates body fat. The equipment is veryexpensive and limited in availability.

Other Methods22%

At Tanita Corporation, werecognize the importanceof education in helping to make the concept ofbody composition analysisunderstandable. We believe people should know what methodsof measurement exist and how these tech-niques work in order to decide which operationis right for their particular needs.

As body composition, rather than bodyweight, becomes an integral part of a person’shealth and fitness evaluation, we predict thatanalytical methods will be driven by scientificresearch and practical application—each withtheir own objectives.

Scientifically, body composition analysiswill become more complex and precise withprediction equations capable of greater individ-ualization. Various techniques may be combinedto create a multi-faceted view of the body wherebody fat and its distribution is just part of aperson’s fitness profile.

In terms of practical applications, bodycomposition analysis will become simpler,more accessible, and easily affordable. It willredefine the traditional scale and re-shape howpeople measure and monitor their bodies.

At Tanita Corporation we are developingproducts to meet all these objectives. Tanita’sgoal is to provide people—whether they aremedical researchers or consumers—with moreinformation about the human body.

23%In Conclusion

Women Have More Body Fat Than MenBy nature, a woman’s body isdeveloped to protect her anda potential fetus. As a result,women have more enzymesfor storing fat and fewerenzymes for burning fat.Additionally, the estrogenwomen have activates fat storing enzymes and causesthem to multiply.

It’s Possible to Have Too Little Body Fat Women athletes involved inhigh performance sports thatemphasize low body weightand extremely low body fatpercentage often experiencea decrease in hormones thatcauses an interruption in themenstrual cycle. The samecondition can occur when awoman is anorexic and herbody goes into a semistarva-tion mode. Over an extendedperiod of time, this can leadto other health risks such asthe loss of bone mass.

Hydration LevelsWomen experience morechanges in hydration levelsthan men because of theirmenstrual cycle, and this canaffect body fat measuring,particularly using the BIAmethod. Retaining fluid mayalso cause weight to fluctuateday-to-day during this period.

And, because weight is one ofthe components in determiningbody fat, it may cause addi-tional variation in the meas-ured body fat percentage.

Female users of BIAproducts should be aware oftheir natural monthly bodycycles. To establish a baselinefor body fat, many womenfind it useful to monitor andchart their readings daily for a month. Afterward, a moni-toring program done at regular intervals can antici-pate monthly fluctuations.

Hormonal changes due topregnancy or menopause mayalso cause water retention andvariations in measuring.Changes in hydration levelscan also be due to food,caffeine or alcohol consump-tion, strenuous exercise,stress or illness, or the takingof prescription drugs, etc.

RememberTo monitor progress, com-pare weight and body fatpercentage measurementstaken under the sameconditions over a period of time. Pay attention to fluctuations caused by menstruation. Stay within the Women’s—not theMen’s—recommendedBody Fat Range!

A Message for Women24%

Many womencustomers havewritten or called

Tanita seekingmore specific

facts about bodyfat and the

female body.We offer the

following additional

information forwomen readers

25%Bibliography

Bioelectrical impedance analysisin body composition measurement:National Institutes of HealthTechnology AssessmentConference Statement. (1996).American Journal of ClinicalNutrition.

Clinical Guidelines on theIdentification, Evaluation,and Treatment of Overweight and Obesity in Adults. (1998).National Heart, Lung, and BloodInstitute and National Institute of Diabetes and Digestive and Kidney Diseases, NationalInstitutes of Health.

Eating and Body Image.(Dec. 1995, Vol.III, #4). HarvardWomen’s Health Watch.

Exercise, Obesity and WeightControl. The Bariatrician.(Winter 1995).

Futrex Technical Literature.

Heymsfield, S.B. (1998).Lecture on Body Composition.Obesity Research Center,St. Luke’s-Roosevelt Hospital,Columbia University College ofPhysicians and Surgeons, NY, NY.

Heyward, V.H. (Sept. 1996).Evaluation of Body Composition.Sports Medicine. Adis Intl. Ltd.

Heyward, V.H. and Stolarczyk, L.M.(1996). Applied BodyComposition Assessment.Human Kinetics.

Jebb, Susan A. (1998).Measuring Body Compositionfrom the Laboratory to the Clinic.Clinical Obesity (18-49).Blackwelll Science Ltd.

Kushner, Kunigk, Alspaugh,Leitch, Schoeller. (Aug. 1990).Validation of BIA as a measure-ment of change in body compo-sition in obesity. AmericanJournal of Clinical Nutrition.

Lohman, T.C. (1992,Monograph #3). Advances inBody Composition Assessment.Current Issues in ExerciseScience. Human Kinetics.

Lukaski, H.C. (1987). Methods for the assessment of humanbody composition: traditional and new. American Journal ofClinical Nutrition.

Margolis, S., Cheskin, L.J. (1997,1998). Weight Control. JohnsHopkins White Papers. The JohnsHopkins Medical Institutions.

Middle-Age Spread. (Aug. 1995,Vol.II, #12). Harvard Women’sHealth Watch.

Nieman, D.C. (1986). Fitness and Sports Medicine: A Health-Related Approach. 3rd Edition.Mayfield Publishing Company.

Nieman, D.C. (1998). TheExercise-Health Connection.Human Kinetics.

Nunez, C., Gallagher, D., Visser,M., Pi-Sunyer, F.X., Wang, Z.,Heymsfield, S.B. (1997).Bioimpedance analysis: evalua-tion of leg-to-leg system basedon pressure contact footpadelectrodes. Medicine and Sciencein Sports and Exercise. AmericanCollege of Sports Medicine.

Pi-Sunyer, F.X. (Oct.1993,Vol. 119,#7). Medical Hazards of Obesity.Annals of Internal Medicine.American College of Physicians.

Tanita Technical Literature.

Tsui, E.Y.L., Gao, X.J., Zinman, B.(Mar. 1998). BioelectricalImpedance Analysis (BIA) Using Bipolar Foot Electrodes in Assessment of BodyComposition in Type 2 DiabetesMellitus. Diabetic Medicine.

Williams, D.P., Going, S.B.,Milliken, L.A., Hall, M.C.,Lohman, T.G. (1995). Practicaltechniques for assessing bodycomposition in middle-aged andolder adults. Medicine andScience in Sports and Exercise.American College of SportsMedicine.

Yet Another Word on Weight.(Aug. 1998, Vol. V, #12).Harvard Women’s Health Watch.

An Introduction 01

Body Composition 04

Reference Models 06

Basic Terms 08

Determining Obesity 10

Calipers 12

Dunk Tank 14

BIA 16

Tanita BIA 18

NIR 20

DEXA 21

Other Methods 22

In Conclusion 23

A Message for Women 24

Bibliography 25

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understanding

body fat analysis

understanding

body fat analysis

Tanita Corporation of America Inc. 847 640 9241 phone2625 South Clearbrook Drive 847 640 9261 fax Arlington Heights, Illinois 60005 www.tanita.com

©2000 Tanita Corporation of America Inc. All rights reserved.(TBF-B7.3) 10M/4-00 HDI. Printed in USA.

Tanita, the world leader in precision electronic scales,is committed to the research and development ofproducts that help people achieve a healthier life.In 1992, the company introduced the world’s first integrated body fat monitor and scale for professionaluse based on BIA (bioelectrical impedance analysis).Since then, Tanita has adapted this technology for the consumer market.

For more information on Tanita’s complete productoffering, including a full line of professional andhome-use body fat monitors, or answers to technicalquestions, call toll free 1-800-TANITA-8.

Who is Tanita?

Version 2.1

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