BPK303 Weight for Height Spring 2014

Desirable Body Weight Desirable, ideal, optimal “What weight should I be?” Weight for height Weight for height with frame size Weight with optimal % body fat BMI - Body Mass Index

Weight for Height Epidemiologists needed a measure of obesity Often questionnaire data on height and weight alone “Ideal” and “Desirable” Weight tables Metropolitan Life Weight for Height Tables

Weight for Height Tables Metropolitan Insurance Co., 1983, weights at ages 25-59 based on lowest mortality. Weight in pounds according to frame (in indoor clothing weighing 3 lbs., shoes with 1" heels).

Frame Size Estimate of Skeletal Proportion

Weight for Optimal % Body Fat If you know the current % body fat, weight for any optimal % body fat can be calculated. Consensus of an expert panel (1986). Arbitrary cut-off points.

Calculation of optimal weight range 1. Calculate Fat Weight (FW) FW = body weight x Ft Where Ft = fractional expression of % body fat 2. Calculate Fat-Free Weight (FFW) FFW = Body Weight – FW 3. Calculate the desired target weight (TW) TW = FFW / (1 – Fx) Where Fx = fractional expression of % body fat

Example Calculation: Young Male Current weight =100kg, %body fat = 34% 1. Calculate Fat Weight (FW) FW = body weight x Ft FW = 100 x .34 = 34kg 2. Calculate Fat-Free Weight (FFW) FFW = Body Weight – FW FFW = 100 – 34 = 66kg 3. Calculate the desired target weight (TW) TW = FFW / (1 – Fx) @ 12%; TW = 66 / (1 - .12) = 66 / 0.88 = 75kg @ 18%; TW = 66 / (1 - .18) = 66 / 0.82 = 80.5kg

Weight range taking into account error in determination of % body fat 95% confidence estimates of % body fat % Fat (1.96 x S.E.E.) 34 (1.96 x 3.7) = 26.7 to 41.3% body fat 95% confidence estimates of FFW are: upper limt FFW = 100 – 26.7 = 73.2kg lower limit FFW = 100 – 41.3 = 58.7kg Lower limit for target weight at 12% body fat TW = 58.7 / (1 - .12) = 58.7 / 0.88 = 71.6kg Upper limit for target weight at 18% body fat TW = 73.2 / (1 - .18) = 73.2 / 0.82 = 83.2kg

Body Mass Index (Quetelet Index - 1833)

Quetelet (1833) [WT] = HT2 [WT]2 = HT5 → [WT] = HT2.5 Tall adults are more linear than short adults. Fully developed individuals: the weight of an individual at different heights is related to the square of the stature: [WT] = HT2 During development: the squares of weight were related to the fifth powers of height: [WT]2 = HT5 → [WT] = HT2.5

Canada Fitness Survey (1981) (20-29 years old)

Correlational Analysis of Weight (WT) and Height (HT) indices in a sample of SFU Kin 303 students (aged 18–25 years) Ward R, Anderson G. 2012 (unpublished)

Sum of 6 Skinfolds vs BMI KIN-Scale Males and Females

Sum of corrected Limb Girths Ross et al. 1988 Correlations of BMI with sums of selected anthropometric measures (Canada Fitness Survey 1981) Sum of 5 Skinfolds Sum of corrected Limb Girths Sum of Bone Breadths Males 0.67 0.56 0.36 Females 0.72 0.48 0.42 Correlations of BMI are “good” with sum of skinfold corrected-girths and even bone widths

Correlational Analysis of Weight (WT) and Height (HT) indices in a sample of SFU Kin 303 students (aged 18–25 years) Ward R, Anderson G. 2012 (unpublished)

Percentage body fat as measured by dual-energy X-ray absorptiometry (DXA %fat) versus BMI and 1/BMI in women from 3 study sites combined. Reproduced from Gallagher (2000)

Percentage body fat by dual-energy X-ray absorptiometry (DXA %fat) versus 1/BMI by sex for each of the study sites. Reproduced from Gallagher (2000)

Predicted percentage body fat by sex and ethnicity based on 4-C percentage body fat

Children & Youth During development: the squares of weight were related to the fifth powers of height: [WT]2 = HT5 → [WT] = HT2.5

B-values of height predicting weight in yearly age groups for Canada Fitness Survey (CFS) and Coquitlam Growth Study (COGRO) boys and girls

CDC BMI Growth Charts

BMI BMI is not an indicator of body fat in individuals it is a measure of weight for height It can be useful as a population screening and awareness device, but not in individual prescription May be useful used in conjunction with other measures