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 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
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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 Calculations
Method 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