Assessment of Energy Needs

David L. Gee, PhDProfessor of Food Science and NutritionCentral 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 CO2 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=18.8-96.8)– 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=-161+10(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:-393-401 (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 + O2 -> CO2 + H2O + energy

• Metabolic Carts

• Hand-held Indirect Calorimeters

Oxidation of glucose• Glucose + 6O2 -> 6CO2 + 6H2O + 673Cal/mol

• 673/6 = 112 Cal/mol O2

• Respiratory Quotient (RQ) = Respiratory Exchange Ratio (RER) = CO2/O2

• RQCHO = 6/6 = 1.0

Oxidation of Fat• Palmitate + 23O2 -> 16CO2 + 16H2O + 2398Cal/mol

• 2398/23 = 104 Cal/mol O2

• RQ = 16/23 = 0.7

Oxidation of Amino Acids• RQ for amino acids and the energy produced per

mol of O2 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 O2

• l O2/min x 5.0 Cal/lO2 = Cal/min• example:

– VO2 = volume of O2 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 O2

• Example– if: VO2 = 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 CalculationsMethod 3 - using total RQ• if VO2 = 0.2 l/min and VCO2 = 0.17

l/min• then RQ = 0.17 / 0.2 = 0.85

• if RQ = 0.85, then 4.862 Cal/lO2

• 0.2 x 4.862 = 0.97 Cal/min• 0.97 x 1440 = 1400 Cal/day

Determination of VO2 and VCO2

• Go to the Word document on Indirect Calormetry Calculations