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Dieting & Weight Loss – RER, Calories Burned and Fuel Percentage

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How can we know what our body is using for energy?

Based on the chemical reactions shown above, we can calculate what researchers call the respiratory exchange ratio (RER) (or respiratory quotient (RQ)) for a given time period. RER is equal to the amount of CO2 exhaled divided by the amount of O2 inhaled.

  • RER = CO2 / O2
  • RER of glucose 6 CO2 /6 O2 = 1.0
  • RER for the triglyceride 114 CO2 / 163 O2 = 0.70
  • RER for the protein 63 CO2 / 77 O2 = 0.82

If we measure a person’s gases during a period of time we can calculate a few things. For example, say that during one hour a person consumed 15 liters of oxygen and expired 12 liters of carbon dioxide; we can first calculate their RER for that hour: 

RER  =  12/15  =  0.80

We can find the RER of 0.80 on the table below and follow it over to the calorie source columns. At an RER of 0.80 this individual would be using approximately 33 percent carbohydrates and 66 percent fat to fuel his or her metabolism. We will assume that the contribution from amino acids toward energy production during that time is minimal. This is a fair assumption for a healthy person not engaged in prolonged fasting or endurance exercise during this time. Furthermore, we can estimate metabolic rate by multiplying the amount of O2 consumed (15 L) by the Caloric Value for 1 liter of oxygen for an RER = 0.80. Their metabolic rate would be: 

15 × 4.801 = 72 Cal/hour

 

 

 

Thermal Equivalent of O2 and CO2 For Nonprotein RER

Respiratory Energy

Ratio (RER) 

 O2

Calories/Liter

CO2

Calories/Liter 

Carbohydrate

(%)

Fat

(%)

0.707

4.686

6.629

0

100.0

0.71

4.690

6.606

1.1

98.9

0.72

4.702

6.531

4.76

95.2

0.73

4.714

6.458

8.4

91.6

0.74

4.727

6.388

12.0

88.0

0.75

4.739

6.319

15.6

84.4

0.76

4.751

6.253

19.2

80.8

0.77

4.640

6.187

22.8

77.2

0.78

4.776

6.123

26.3

73.7

0.79

4.788

6.062

29.9

70.1

0.80

4.801

6.001

33.4

66.6

0.81

4.813

5.942

36.9

63.1

0.82

4.825

5.884

40.3

59.7

0.83

4.838

5.829

43.8

56.2

0.84

4.850

5.774

47.2

52.8

0.85

4.862

5.721

50.7

49.3

0.86

4.875

5.669

54.1

45.9

0.87

4.887

5.617

57.5

42.5

0.88

4.899

5.568

60.8

39.2

0.89

4.911

5.519

64.2

35.8

0.90

4.924

5.471

67.5

32.5

0.91

4.936

5.424

70.8

29.2

0.92

4.948

5.378

74.1

25.9

0.93

4.961

5.333

77.4

22.6

0.94

4.973

5.290

80.7

19.3

0.95

4.985

5.247

84.0

16.0

0.96

4.998

5.205

87.2

12.8

0.97

5.010

5.165

90.4

9.58

0.98

5.022

5.124

93.6

6.37

0.99

5.035

5.085

96.8

3.18

100

5.047

5.047

100

0

 

                                  Click for PDF of RER Table

 

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