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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

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Assessment of energy needs l.jpg

Assessment of Energy Needs

David L. Gee, PhD

Professor of Food Science and Nutrition

Central Washington University


Reasons to assess energy needs l.jpg

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)


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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%


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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


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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.”


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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


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Estimation of Total Energy Expenditure is even less accurate

  • TEE = REE + Activity + TEF + Injury factors

  • estimations of

    • activity

    • TEF

    • injury factors

  • are crude estimates


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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


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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


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Oxidation of Fat

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

  • 2398/23 = 104 Cal/mol O2

  • RQ = 16/23 = 0.7


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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


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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


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Indirect Calorimetry CalculationsMethod 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


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Indirect Calorimetry CalculationsMethod 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


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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


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Determination of VO2 and VCO2

  • Go to the Word document on Indirect Calormetry Calculations


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