Assessment of Energy Needs David L. Gee, PhD Professor of Food Science and Nutrition Central Washington University

Reasons to assess energy needs Energy needs are highly variable Prevent underfeeding –decrease organ mass and function –impaired wound healing –impaired immune response Prevent overfeeding –excessive CO 2 production Respiratory acidosis –Hyperglycemia and insulin resistance –fluid retention and fat gain (fatty liver)

Estimation of Resting Energy Expenditure (REE) with Prediction Equations Harris-Benedict Equation (1919) –based on gender, weight, height, age WHO Equations (1982) –based on gender, weight, age Errors in estimation: –Standard deviation = 10% –95% confidence interval = 20%

Validation of Several Established Equations for Resting Metabolic Rate in Obese and Nonobese People. Frankenfield et al., JADA 103:1152(2003) 130 healthy adults (BMI= ) –98% white Compared equations to indirect calorimetry –Harris-Benedict –Adjusted Harris-Benedict (25% of excess wt) –Owen (1986) –Mifflin (1990) Men: kcal/d=5+10(wt)-6.25(ht)-5(age) Women: kcal/d= (wt)+6.25(ht)-5(age) Wt=kg, ht=cm,age=yrs

Accurate Determination of Energy Needs in Hospitalized Patients. Boullata et al., JADA 107: (2007) 395 hospitalized patients Compared prediction equations against measured REE –Harris-Benedict, Mifflin, 6 others Conclusions: –Most accurate was Harris-Benedict multiplied by 1.1, but only 62% were within 10% of measured REE –“No equation accurately predicted REE in most hospitalized patients … only indirect calorimetry will provide accurate assessment of energy needs.”

Why prediction equations fail… Equations based on gender, height, weight and age explain ~ 80% of individual variation in REE Sources of other variations –Mass of various tissues Visceral tissues 10x more active than muscle tissue at rest and 100x more active than adipose Knowing body composition based on 2-component or 4-component models still inadequate

Estimation of Total Energy Expenditure is even less accurate TEE = REE + Activity + TEF + Injury factors estimations of –activity –TEF –injury factors are crude estimates

Indirect Calorimetry Estimation of energy expenditure based on respiratory gases –oxygen consumed –carbon dioxide produced Nutrient + O 2 -> CO 2 + H 2 O + energy Metabolic Carts Hand-held Indirect Calorimeters

Oxidation of glucose Glucose + 6O 2 -> 6CO 2 + 6H 2 O + 673Cal/mol 673/6 = 112 Cal/mol O 2 Respiratory Quotient (RQ) = Respiratory Exchange Ratio (RER) = CO 2 /O 2 RQ CHO = 6/6 = 1.0

Oxidation of Fat Palmitate + 23O 2 -> 16CO H 2 O Cal/mol 2398/23 = 104 Cal/mol O 2 RQ = 16/23 = 0.7

Oxidation of Amino Acids RQ for amino acids and the energy produced per mol of O 2 varies for each amino acid RQ for average protein is 0.85 Contribution of protein oxidation is ignored because: –small compared to fat and glucose –RQ at rest is typically close to 0.85 –protein oxidation during short-term exercise is very small compared to fat and glucose –To measure protein oxidation, one needs to collect 24hr urine to measure total urea production

RQ (RER) Tables RQ or RER can be used to: –Determine the calories burned per liter of oxygen consumed or Liter of carbon dioxide produced –Determine the % of calories produced by burning fats and carbohydrates

Indirect Calorimetry Calculations Method I (rough estimate) Approximately 5.0 Cal/l O 2 l O 2 /min x 5.0 Cal/lO 2 = Cal/min example: –VO 2 = volume of O 2 consumed/min = 0.2 l/min –then 0.2 x 5 = 1 Cal/min –if REE, then 1 Cal/min x 1440 min/d = 1440Cal/d

Indirect Calorimetry Calculations Method 2 (not so rough estimate) More accurately: 4.8 Cal/l O 2 Example –if: VO 2 = 0.2 l/min –then: 0.2 x 4.8 = 0.96 Cal/min –if REE, then 0.96 x 1440 = 1382 Cal/d

Indirect Calorimetry Calculations Method 3 - using total RQ if VO 2 = 0.2 l/min and VCO 2 = 0.17 l/min then RQ = 0.17 / 0.2 = 0.85 if RQ = 0.85, then Cal/lO x = 0.97 Cal/min 0.97 x 1440 = 1400 Cal/day

Determination of VO 2 and VCO 2 Go to the Word document on Indirect Calormetry Calculations