Assessment of Body Composition David L. Gee, PhD FCSN 442 - Nutrition Assessment Laboratory

Body Composition Analysis vs. Body Weight Assessment Advantages “Direct” assessment of body fatness Overweight Overmuscled or overfat Athletes Assessing need for weight loss inadequate stores in patients Monitor changes weight loss quality effect of medical therapy

Body Composition Analysis vs. Body Weight Assessment Disadvantages relatively limited database all field methods are estimations false assumptions in all field methods errors by technicians limited understanding by clients

Nutrition and Athletic Performance ACSM/ADA 2000 Position Paper “Body fat assessment techniques have inherent variability, thus limiting the precision with which they can be interpreted.” “With carefully applied skin-fold or BIA,… relative body fat % error of 3% - 4% 15% (12-18%) estimate fat-free mass within 2.5-3.5 kg 50kg (47.5-52.5kg) Would you buy a bathroom scale with this type of accuracy? 110 pounds + 7 pounds

Models of body composition 2 compartment models Fat mass and Fat-free mass Fat mass and Lean body mass LBM includes cell membranes, TG in cells assessment methods using this model skinfold thickness hydrodensitometry bioelectric impedance

Models of body composition 4 compartment models water, protein, fat , minerals Assessment methods using this model isotope dilution dual emmision x-ray absorptiometry (DEXA) computed tomography (CT, CAT) Research techniques Not covered in this course

Skinfold Thickness Advantages: measures double thickness of skin and subcutaneous fat Advantages: inexpensive fast portable large database

Skinfold Thickness Assumptions: predicts non-subcutaneous fat >50% of fat is subcutaneous sites selected represent average thickness of all subcutaneous fat compressibility of fat similar between subjects thickness of skin negligible

Skinfold Thickness Limitations Technician error Skinfold thickness affected by factors other than amount of fat exercise increases skin thickness dehydration reduces skin thickness edema increases skin thickness dermatitis increases skin thickness Poorly predicts visceral fat

Single Site Measurements Tricep skinfold thickness Subscapular skinfold thickness not for estimating body fat determination for comparing against other reference data NHANES II (1097-1980) appendix O (p530-532) (TSF) appendix P (p533-535) (SSF)

Two site measurements Tricep SF and Subscapular SF correlated with body fatness in children fig. 6-32 (p192) Tricep SF and calf SF fig. 6-33 (p 192)

Multiple Site Measurements many sites many equations table 6-9 (p193) Jackson & Pollock table 6-10 (p193) Durnin & Womersley density and %body fat Siri % BF = (495/BD) – 450 Brozek % BF = (457/BD) - 414

Circumference Measurements Katch and McArdle Principle: measure two “fat” sites measure one “muscle site” estimate fat and lean body mass. Very limited database Easy to do

Hydrodensitometry

Hydrodensitometry Principle: two compartment model density related to relative amounts of two compartments D(fat) = 0.90 g/ml D(lbm) = 1.10 g/ml D(water) = 1.00 g/ml

Hydrodensitometry Density = Body weight/Body volume How does one estimate body volume? Archimedes principles: volume of submerged object = volume of water displaced weight in air - weight underwater = weight of water displaced

Hydrodensitometry calculate %BF from BD To calculate body density wt of water displaced = vol of water displaced Wt of water displaced = vol of body (BV) Since weight of water displaced = weight in air - weight underwater BV = BW-UBW To calculate body density BD = BW / BV calculate %BF from BD

Hydrodensitometry Calculations DATA BW(air) = 180 lbs = 81.6 kg BW(water) = UWW = 3.6 kg RV = 1.30 L, est GI gas vol = 0.1 L Density of water @ 77 deg = 0.997 kg/L CALCULATIONS BV = (BW-UWW)/.997 – (RV +0.1) BV = (81.6-3.6)/.997 – (1.3+0.1) BV = 78.23 – 1.4 = 76.83 L

Hydrodensitometry Calculations BV = 76.83 L BD = BW / BV = 81.6/76.83 = 1.062 kg/L % BF = (495/BD)- 450 = (495/1.062)-450 %BF = 466.09-450 = 16.09% = 16% Fat mass = 16% x 81.6kg = 13.1 kg Lean mass = 81.6-13.1 = 68.5 kg

Hydrodensitometry: Assumption Density of fat and lean are constant bone density muscle density hydration status GI gas volume is constant

Hydrodensitometry: Limitations Measurement of residual lung volume Precision of underwater weight Cost Non-portable Limited types of subjects

Whole Body Pethysmography Measures body volume by air displacement actually measures pressure changes with injection of known volume of air into closed chamber Large body volume displaces air volume in chamber results in bigger increase in pressure with injection of known volume of air

Whole Body Pethysmography Advantages over hydrodensitometry subject acceptability precision residual lung volume not factor Limitations costs: $25-30K still assumes constant density of lean and fat

Bioelectrical Impedance Analysis 1994 NIH Technology Assessment Conference “BIA provides a reliable estimate of total body water under most conditions.” “It can be a useful technique for body composition assessment in healthy individuals”

Bioelectrical Impedance Analysis BIA measures impedance by body tissues to the flow of a small (<1mA) alternating electrical current (50kHz) Impedance is a function of: electrical resistance of tissue electrical capacitance (storage) of tissue (reactance)

BIA: basic theory The body can be considered to be a series of cylinders. Resistance is proportional to the length of the cylinder Resistance is inversely proportional to the cross-sectional area

BIA: basic theory Volume is equal to length of the cylinder times its area Therefore, knowing the resistance and the length, one can calculate volume. Assuming that the current flows thru the path of least resistance (water) , then the volume determined is that of body water.

BIA: basic theory Assume fat free mass has a constant proportion of water (about 73%) Then calculate fat free mass from body water Assume BW = FFM + FM Then calculate fat mass and %body fat

NHANES III BIA Equations Males FFM = -10.68 + 0.65H2/R + 0.26W + 0.02R Females FFM = -9.53 + 0.69H2/R + 0.17W + 0.02R Where FFM = fat free mass (kg) H = height (cm) W = body weight (kg) R – resistance (ohms) % BF = 100 x (BW-FFM)/BW

BIA Calculations DATA CALCULATIONS R = 520 ohms BW = 170 lbs = 77.3 kg H = 70” = 178 cm CALCULATIONS FFM = -10.68+(0.65H2/R)+0.26W+0.02R FFM = -10.68+(0.65x1782/520)+0.26(77.3)+0.02(520) FFM = -10.6 + 39.6 + 20.1 + 10.4 = 59.5 kg FM = W – FFM = 77.3 – 59.5 = 17.8 kg %BF = (17.8/77.3)x100 = 23%

BIA: Advantages and Limitations costs ($500-$2000) portable non-invasive fast Limitations accuracy and precision no better/worse than hydrodensitometry

Major types of BIA analyzers

BIA Protocol Very sensitive to changes in body water normal hydration caffeine, dehydration, exercise, edema, fed/fasted Sensitive to body temperature Avoid exercise Sensitive to placement of electrodes conductor length vs. height

What is a ‘normal’ % body fat? Classification Males Females Unhealthy range (too low) < 5% < 8% Acceptable range (lower end) 6-15% 9-23% Acceptable range (higher end) 16-24% 24-31% Unhealthy (too high) > 25% > 32% Nieman, 1999 (p195)

Body Composition Data NHANES III – 1988-1994 All adults > 19 yrs Mean % Body Fat Men: 21.9% + 11.6% (SD) Women: 32.4% + 17.8% Mean BMI Men: 26.5 + 7.8 Women: 26.4 + 11.7 Mean waist circumference Men: 95.1 + 18.6 cm (cutpoint > 101.6 cm) Women: 88.6 + 30.2 cm (> 89 cm)

Body Composition Data NHANES III – 1988-1994 Adults with BMI = 18.5-25 Mean % Body Fat Men: 17.6% + 7.8% (SD) Women: 26.7% + 8.9% Mean BMI Men: 22.7 + 3.2 Women: 22.0 + 2.2 Mean waist circumference Men: 84.7 + 8.9 cm (cutpoint > 101.6 cm) Women: 78.0 + 13.4 cm (> 89 cm)

Dual-Energy X-ray Absorptiometry

DEXA, DXA Two different energy level X-rays Lean, fat, and bone mass each reduce (attenuate) the X-ray signal in unique ways Computer analyzes scan point by point to determine body composition Method Low dose radiation 20-30 minutes Applicable to young and old