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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
- 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 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

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

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

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