BODY COMPOSITION

Dr. Kiran SanganiConsultant: Preventive Cardiology &

RehabilitationAsian Heart Institute

• BC refers to the absolute and relative amounts of body constituents.

• It can be assessed on elemental (atomic), chemical, cellular, and tissue system levels.

• Body composition can be measured by lab based and field based methods. However, lab based methods not routinely used but do provide the foundation for simpler field methods.

• Field techniques generally require less complex and more portable equipment, are less costly, and can be applied outside of controlled laboratory conditions.

• Selection of appropriate method is based on the relative precision, reliability, and accuracy of available methods, the availability of appropriate equations, and AFFORDABILITY.

• Percent body fat and fat free mass can be estimated with field techniques with errors of more than 3 % and more than 2.5-3 kg respectively.

Objectives to measure BC

• Since there is a strong correlation between body fat percentage and an increased risk of many chronic diseases like CAD, DM, HTN, and certain types of Cancer, there is a frequent need to assess body composition in the health and fitness field.

• An excessively low level of fat is also detrimental, as evidenced by physiological dysfunction of the chronically undernourished.

• Assessment also useful to establish optimal weight for health and performance in athletes, to formulate dietary guidelines and exercise prescriptions for modifying body composition and evaluating efficacy.

• To monitor changes in composition with growth, maturation, and aging to distinguish normal changes from disease states.

Importance of Body Fat

• Fat is an insulator; it helps your body adapt to heat and cold.

• Fat acts as a shock absorber; it can help protect your body organs and bones from injury.

• Fat helps your body use vitamins effectively.• Fat is stored energy that is available when your body

needs it.• Fat, in reasonable amounts, helps you look your best,

thus increasing your feelings of well-being

Physiological impact of BC changes

Assessment of lean tissue mass and its components is as equally important as fat mass.

• Low levels of lean mass and loss of lean tissue contribute to metabolic complications both directly and indirectly, through impaired functional capacity and reduced physical activity and energy expenditure, hence a greater risk of fat gain.

• Low bone mass and density are primary predictors of risk of osteoporotic fractures.

• Muscle wasting that occurs with certain diseases and with ageing not only decreases muscle strength and the capacity for routine activities but is also a strong correlate of mortality. Therefore interventions to increase lean tissue mass in healthy ageing and clinical populations has to be emphasised upon.

Assessment of Body Composition

• Hydrostatic weighing (Gold Standard)• Bioelectrical Impedance Analysis (BIA)• Dual energy X-ray absorptiometry (DEXA)• Height and Weight• Body mass index• Waist to Hip Ratio• Waist Circumference• Skin fold measurement

Hydrostatic Weighing (HSW)

• “Gold standard” developed by Behnke and Pace in the 1940’s

• Determine the density of fat and muscle

• Density = MASS / VOLUME• Archimede’s principle of water

displacement

• Weight in air - weight in water = mass of water displaced.

• Underwater weighing is based upon Archimedes Principle which states that the buoyant force on a submerged object is equal to the weight of the fluid that is displaced by the object.

• We can use this principle to determine a person's percentage of body fat because the density of fat mass and fat-free mass are constant. Lean tissue, such as bone and muscle, are more dense than water, and fat tissue is less dense than water.

• Basically, muscle sinks and fat floats. Therefore, a person with more body fat will weigh less underwater and be more buoyant. Someone with more muscle will weigh more underwater.

Hydrostatic Weighing• Purpose: the aim of underwater weighing is to

measure the density of the body, and from that figure calculate percentage body fat

• Equipment: Hydrostatic weighing tank, including underwater mounted chair and scale, weighted belt and nose clip. A more simple set up may include a chair and scale suspended from a diving board over a pool or hot tub.

• Description: The dry weight of the subject is first determined. The subject, in minimal clothing, then sits on a specialized seat, expels all the air from their lungs, and is lowered into the tank until all body parts are emerged. The person must remain motionless underwater while the underwater weight is recorded. This procedure is repeated several times to get a dependable underwater weight measure.

– Scoring: Body density = Wa / (((Wa - Ww) / Dw) - (RV + 100cc)), where Wa = body weight in air (kg), Ww = body weight in water (kg), Dw = density of water, RV = residual lung volume, and 100cc is the correction for air trapped in the gastrointestinal tract. The body density (D) can be converted to percent bodyfat (%BF) using the Siri equation.

• % Body Fat = (495 / Body Density) - 450

Sources of Error in HSW• Residual lung volume

• Intestinal gas

• Water density/ water temperature

• Individual variability in density of lean tissue

• Variation in bone mineral density

• Time to fill the tank

• Problems with subject panicking

Bioelectrical Impedance Analysis• Introduction: BIA is a rapid, non-invasive, and relatively inexpensive

method of estimating fat and FFM. Although the relative prediction accuracy is similar to that of the skinfold method, BIA may be preferable in some settings because it does not require a high degree of technical skill and is generally more comfortable, requires minimal cooperation, and intrudes less on privacy.

• Principle: Bioelectrical impedance measures the resistance of body tissues to the flow of a small, harmless electrical signal. The proportion of body fat can be calculated as the current flows more easily through the parts of the body that are composed mostly of water (such as blood, urine & muscle) than it does through bone, fat or air. It is possible to predict how much body fat a person has by combining the bioelectric impendence measure with other factors such as height, weight, gender, fitness level and age.

Equipment: A Bioelectric Impedance Analyzer is a sophisticated scientific instrument, used in research and analysis. On a budget level, many bathroom type weighing scales are also available with a Bioelectric Impedance Analyzer, which is two built-in footpad electrodes on the base of the scale which the person stands on.

Description: As the bioelectric impendence device measures the resistance of body tissues to the flow of a small electrical signal, the person being measured should not be in contact with any other non conducting surface, with legs apart and arms away from the body. Some devices require a pair of electrodes to be placed on the hand and wrist, and another pair placed on the ankle and foot (usually opposite sides of the body), while other devices simply require you to stand on two foot plates. Follow the instructions of your particular device.

• A new technology, called Direct-Segmental Bioelectrical Impedance Analysis (DSM-BIA), is much more accurate than traditional BIA. This technology utilizes eight points of tactile electrodes while conveying multiple frequencies of currents through the body. Usually, frequencies higher than 10 kHz allow for the measurement of both intracellular and extracellular water. Single frequency BIA can only detect extracellular water. Validation studies have proven that the DSM-BIA machines are 96-98% accurate when compared with the gold standards of body composition, hydrostatic weighing and DEXA testing.

• NOTE : Although BIA has an excellent theoretical basis for making good body composition predictions, several important protocols must be followed for the results to be accurate and repeatable. Since the technique is dependent on electrical conductivity through the lean mass, the hydration state of the subject can alter the results. If someone having a BIA test is not well hydrated, the electrical current will not be conducted through the lean mass as well, so the subject will appear to have more fat mass than they actually do. Therefore, it is critically important that the person being measured be in a well-hydrated state. It is generally believed that drinking alcohol, exercising, consuming large amounts of coffee, and spending time outside in hot and humid weather within 24 hours of a BIA test lead to sufficient dehydration that the results will not be accurate. Since serious athletes exercise most days, this technique may provide results that indicate more body fat than they really have. Therefore, athletes who are measured with this technique should wait until after a day of rest and should make certain they are well hydrated. An easy hydration check is to see if the urine is clear. The more clear it is, the better hydrated you are.

Dual Energy X-ray AbsorptiometryDEXA Scan

Dual-energy X-ray absorptiometry (DEXA) is the latest, most accurate, and most expensive means of determining body composition, and it is generally considered the current gold standard for this purpose. The information you can derive from a full-body scan on an athlete is invaluable, including bone density; body fat percentage; lean body mass; fat mass; and the distribution of fat and lean tissue in the arms, trunk, and legs. DEXA output even provides the differences in lean mass and fat mass between the left and right sides. This information can be particularly important for athletes who wish to develop symmetrical bodies or who, because of the nature of the sport, need to produce the same muscular power in each leg or in each arm.

• Principle : DEXA works by passing two X-ray beams through the subject and measuring the amount of X ray absorbed by the tissue it has passed through. One beam is high intensity and one is low intensity, so the relative absorbance of each beam is an indication of the density of the tissue it has passed through. The higher the tissue density, the greater the reduction in X-ray intensity. DEXA uses a whole body scanner that has two low dose x-rays at different sources that read bone and soft tissue mass simultaneously. The sources are mounted beneath a table with a detector overhead. The scanner passes across a person's reclining body with data collected at 0.5 cm intervals. A scan takes between 10-20 minutes.

• Safety : It is safe and noninvasive with little burden to the individual, although a person must lie still throughout the procedure. The amount of radiation energy that is used with DEXA is extremely small. You would need to have approximately 800 full-body DEXA scans before being exposed to the same amount of radiation received from one standard chest X ray. In fact, the level of radiation is so low that DEXA is approved by the FDA as a screening device to predict body composition. Usually, X-ray devices are reserved as diagnostic instruments because of the amount of radiation they impart, but not so for DEXA.

• DEXA is fast becoming the new "gold standard" because it provides a higher degree of precision in only one measurement and has the ability to show exactly where fat is distributed throughout the body. It is very reliable and its results extremely repeatable; in addition, the method is safe and presents little burden to the subject. Although this method is not as accurate in measuring the extremely obese and the cost of equipment is high, DEXA is quickly moving from the laboratory setting into clinical studies.

Near Infrared Interactance• A fiber optic probe is connected to a digital

analyzer that indirectly measures the tissue composition (fat and water) at various sites on the body. This method is based on studies that show optical densities are linearly related to subcutaneous and total body fat. The biceps is the most often used single site for estimating body fat using the NIR method. The NIR light penetrates the tissues and is reflected off the bone back to the detector. The NIR data is entered into a prediction equation with the person's height, weight, frame size, and level of activity 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 relatively inexpensive. However, the amount of pressure applied to the fiber optic probe during measurement may affect the values of optical densities, and skin color and hydration level may be potential sources of error. To date, studies conducted with this method have produced mixed results; a high degree of error has occurred with very lean and very obese people; and the validity of a single-site measurement at the biceps is questionable. Numerous sources report that more research is needed to substantiate the validity, accuracy and applicability of this method.

Too Much Body Fat Too Little Body Fat Good Body Fat

 

The Bodpod

Description: One of the newest forms of body composition testing involving state of the art technology, developed by Life Measurements Instruments, Concord, CA (now taken over by COSMED). The use of Bod Pod correlates nicely with the concept of hydrostatic weighing (underwater weighing). Instead of using water to measure body volume, the Bod Pod uses air displacement to measure body volume. Measurement time takes roughly 5 to 8 minutes per individual.

How accurate is it? If each test is performed correctly according to the recommended guidelines, there is a ± 3% error.

Factors that may affect accuracy of the Bod Pod• Hydration status and increases in muscle temperature can

adversely affect calculation results• Also, it is imperative to breath normal, remain still, and keep

hands in lap while being assessed by the Bod Pod (any slight movement or change in breathing pattern may affect results)

Advantages• Does not require getting wet• Not difficult to operate• Measurement time is short• Well suited for special populations (children, obese,

elderly, and disabled persons)Disadvantages• Very expensive ($30,000 - $40,000)• Only a few facilities have the Bod Pod

Skinfold measurement

• It’s a quick, noninvasive and inexpensive method

• The fat% value obtained using skinfold equations is typically within 4% of the value measured using underwater weighing

• It is based on the assumption that, as one gains adipose tissue, the increase in skinfold thickness will be proportional to the additional fat weight

• Because one’s 50% to 70% of adipose tissue is stored subcutaneously, this assumption holds true in most cases

• Procedure: Estimation of body fat by skinfold thickness measurement can be done from 3 to 9 different standard anatomical sites around the body. The right side is usually only measured (for consistency). The tester pinches the skin at the appropriate site to raise a double layer of skin and the underlying adipose tissue, but not the muscle. The calipers are then applied 1 cm below and at right angles to the pinch, and a reading in millimeters (mm) taken two seconds later. The mean of two measurements should be taken. If the two measurements differ greatly, a third should then be done, then the median value taken.

Vertical fold Posterior midline of the upper arm Halfway between the acromion (shoulder) and olecranon processes (elbow) Arm held freely to the side of the body

1) Triceps 2) Chest

Diagonal fold Men: one-half the distance between the anterior axillary line (crease of the underarm) and the nipple Women: one-third of the distance between the anterior axillary line and the nipple

Vertical or Horizontal fold Midaxillary line at the level of the xiphoid process of the sternum

3) Midaxillary

4) Abdominal

Vertical (modern technique) 2 cm or 1" to the right side of the umbilicus

5) Subscapular

Diagonal fold 1 to 2 cm below the inferior angle of the scapula

6) Suprailiac

Diagonal fold Anterior axillary line (modern technique) immediately superior to the iliac crest in line with the natural angle of the iliac crest taken Mid-axillary line (traditional technique) Superior to the iliac crest

7) Thigh

Vertical fold Anterior midline of the thigh Midway between the proximal border of the patella (upper knee) and the inguinal crease (hip)

8) Biceps

Vertical fold Anterior aspect of the arm over the belly of the biceps muscle 1 cm above the level used to mark the triceps site

9) Calf

Vertical fold Maximum circumference of calf on the midline of medial border 

Generalized Skinfold Equations

Men• 7-site formula (Chest, Midaxillary, Triceps, Subscapular, Abdomen, Suprailiac, Thigh)

Body Density = 1.112 – 0.00043499 x (sum of 7 skinfolds)+ 0.00000055 x (sum of 7 skinfolds)2

- 0.00028826 x (age)

• 3 -site formula (Chest, Abdomen, Thigh)Body Density = 1.10938 – 0.0008267 x (sum of 3 skinfolds)

+ 0.0000016 x (sum of 3 skinfolds)2

- 0.0002574 x (age)

Female• 7-site formula (Chest, Midaxillary, Triceps, Subscapular, Abdomen, Suprailiac, Thigh)

Body Density = 1.097 – 0.00046971 x (sum of 7 skinfolds)+ 0.00000056 x (sum of 7 skinfolds)2

- 0.00012828 x (age)

• 3 -site formula (Triceps, Suprailiac, Thigh)Body Density = 1.1099421 – 0.0009929 x (sum of 3 skinfolds)

+ 0.0000023 x (sum of 3 skinfolds)2

- 0.0001392 x (age)

Skinfold Method

• Cheap, easy to use, portable, all age groups, large numbers

• Errors occur: selection of the site: but single observer can produce reliable results

• Skin compressibility varies in individuals

• Excess fluid if repeated too many times

• Undress to get to certain sites

Body Fat Percentage normsDescriptionDescription WomenWomen MenMen

Essential fatEssential fat 10–12%10–12% 2–4%2–4%

AthletesAthletes 14–20%14–20% 6–13%6–13%

FitnessFitness 21–24%21–24% 14–17%14–17%

AcceptableAcceptable 25–31%25–31% 18–25%18–25%

OverweightOverweight 32-41%32-41% 26-37%26-37%

ObeseObese 42%+42%+ 38%+38%+

Height & Weight• “Consulting room” instrument.

Height : Record height in cms or inches with shoes removed.1 inch = 2.54 cms1 meter = 100 cms

Weight : Record weight in kgs or pounds with shoes removed.1 kg = 2.2 pounds (lbs)

Body Mass Index

• BMI = Weight (kgs) / (Height in meters)2

• It is used to describe an individual’s relative weight for height, and is significantly correlated with total body fat content.

• “Overweight” = “over-fat?” or “over muscled?”

BMI

With a BMI With a BMI of:of:

You are You are considered:considered:

< 18.5< 18.5 UNDERWEIGHTUNDERWEIGHT

18.5 - 24.918.5 - 24.9 HEALTHY WEIGHTHEALTHY WEIGHT

25.0 - 29.925.0 - 29.9 OVERWEIGHTOVERWEIGHT

30 or higher30 or higher OBESEOBESE

DISEASE RISK

Men </= 102 cmWomen </= 88 cm

Men > 102 cmWomen > 88 cm

_ _

_ _

Cirfcumferences

• Abdomen• Arm• Buttocks / Hips• Calf• Forearm• Mid-thigh• Waist

Waist circumference

• Strong indicator of health risk• >102 cm in men or >40 inches• >88 cm in women or >35 inches

However ! For Asian population

> 90 cm for men> 90 cm for men> 80 cm for women> 80 cm for women

Waist to Hip Ratio

• Comparison between circumdference of waist and hip. • Represents distribution of body weight, and thereby body

fat.• Waist circumference measured at 1 inch above the

umbilicus / or at umbilicus / at level of iliac crest.• Hip circumference measured at largest circumference

around the buttocks.• Health risk is very high if

WHR > 0.95 for young men, 0.86 for young women

WHR > 1.03 for men > 60 yrs, 0.9 for women > 60 yrs

RISK

Age Low Moderate High Very High

Men

Women

20-2930-3940-4950-5960-69

20-2930-3940-4950-5960-69

< 0.83< 0.84< 0.88< 0.90< 0.91

< 0.71< 0.72< 0.73< 0.74< 0.76

0.83-0.880.84-0.910.88-0.950.90-0.960.91-0.98

0.71-0.770.72-0.780.73-0.790.74-0.810.76-0.83

0.89-0.940.92-0.960.96-1.000.97-1.020.99-1.03

0.78-0.820.79-0.840.80-0.870.82-0.880.84-0.90

> 0.94> 0.96> 1.00> 1.02> 1.03

> 0.82> 0.84> 0.87> 0.88> 0.90

The Pear versus the AppleWaist-to-Hip Ratio

Definition: waist circumference measurement divided bythe measurement of the widest circumference around the hips.

Men’s Goal:Men’s Goal:Men<0.95

Women’s Goal:Women’s Goal:<0.80

Visceral Fat vs. Subcutaneous Fat

FACTORS INFLUENCING BODY WEIGHT & COMPOSITION

• Age• Sex• Genetic Factors• Environmental Factors• Social & Behavioral factors

• 30 yr old doing Bruce protocol has to stop at 9 min due to muscle cramps. He had reached a HR of 171. Calculate VO2max using appropriate formula.

• 33.524 mlO2/kg/min

• A client measuring 5’4” has a BMI of 25 wants to burn 250 calories at the end of 30 min. Calculate the intensity at which he should exercise?

• 7.21 METS