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Assessing Your Patientís Weight and Body Composition
"Ideal" Body Weight
A quick estimate of ideal body weight for height (without shoes) may be obtained for adults with a medium frame by the following simple equations:
: 100 lbs. for first 5 feet + 5 lb/each additional inch.
: 106 lbs. for first 5 feet + 6 lb/each additional inch.
This estimate should be decreased by 10% for a small frame or increased by 10% for a large frame. Generally speaking, 10-20% over ideal body weight is considered overweight, 20% over ideal body weight is considered obese. (Percent Ideal Body Weight = (current weight/ ideal weight X 100) A loss of over 10% body weight in 6 months is considered a severe weight loss and may indicate malnutrition.
Body Mass Index (BMI)
BMI = Weight (kg) / Height 2 (m) [1 kg = 2.2 lb; 1 in = 2.54 cm] or [Weight (lb) x 705 / Height (in)]
This ratio is often used to evaluate obesity in relation to risk factors. Desired BMI for health maintenance in adults is 20 - 26 kg/m 2. A value between 26 and 30 signifies overweight. A BMI over 30 kg/m 2 signifies obesity with associated health risks. Values above 40 kg/m 2 indicate severe obesity. The BMI-related health risk is increased by the presence of comorbid conditions such as diabetes, hypertension or cardiovascular disease. (See BMI tables on page 7)
Using anthropometrics is a good way to establish whether the BMI is attributed mainly to muscle or to fat.
- Triceps Skinfold Measurement (TSF) estimates stored body fat. The TSF is taken at the midpoint of the non-dominant arm between the acromion and the olecranon bones. After the subcutaneous tissue on the underside of the arm is pulled away from the triceps muscle, the subcutaneous fat is measured with skinfold calipers. This value is evaluated using a reference table, with a value greater than the 95th percentile signifying obesity.
Body Mass Index Tables
2. Mid-Arm Circumference (MAC) is also taken on the midpoint of the non-dominant arm with a metric tape. This measurement estimates muscle mass.
3. Mid-Arm Muscle Circumference (MAMC) estimates the skeletal muscle mass based on the MAC and the TSF measurements. MAMC= MAC - 3.14 (TSF). The MAMC is then evaluated using a reference table. A value greater than the 90th percentile signifies obesity. Remember to keep your units consistent.
Bioimpedence Analysis (BIA)
A bioimpedence machine measures total body resistance by passing an electrical current through surface electrodes on the patientís upper and lower extremities. Because adipose tissue is a poor conductor, and lean tissues, especially fluid compartments, are good conductors, the resistance is higher with higher levels of total body fat. Studies suggest that BIA improves the prediction of total body fat and water compared to body weight, height or anthropometry used either alone or in combination.
To maintain body weight, caloric intake must balance caloric expenditure. Energy requirements must meet needs of basal metabolism and physical activity, and should also compensate for increased demands due to illness or injury.
- Basal Energy Expenditure (BEE)
Harris-Benedict Equation for daily basal caloric requirement:
: 665 + (9.6 x IBW) + (1.9 x Ht) - (4.7 x age) kcal/day IBW = Ideal body weight in kg
: 66.5 + (13.8 x IBW) + (5 x Ht) - (6.7 x age) kcal/day Ht = Height in cm
Total energy requirement
Compute the patientís BEE using Harris-Benedict and multiply the result by factors ranging from 1.2-1.3 (for a sedentary lifestyle) to 2.5 (for patients with severe catabolic needs due to burns, trauma). Use a factor of 1.4-1.5 for moderate activity level. A caloric deficit of 3500 kcal corresponds to loss of one pound. A patient who reduces total energy requirement by 500 kcal per day will lose 1 pound per week (500 x 7= 3500 kcal = 1 lb of fat).