Lassie’s resting metabolic rate was determined to be 358 mL min -1 with a respir
ID: 143214 • Letter: L
Question
Lassie’s resting metabolic rate was determined to be 358 mL min-1 with a respiratory exchange ratio of 0.77, with light exercise (walking) Lassie’s metabolic rate increased to 662 mL min-1 with a respiratory exchange ratio of 0.83, and for a brief period of time, Lassie’s metabolic rate was maximal at 3550 mL min-1 with a respiratory exchange ratio of 1.36 while he was running up a steep gradient. How much CO2 was Lassie excreting at each of these three time points? Consider one day (24 hours) in which 60% of the time Lassie was at his basal (resting) metabolic rate, 39% of his time was at light exercise (662 mL min-1) and the remaining 1% of his time was at maximal exertion (3550 mL min-1). Assuming Lassie’s been eating a dogfood diet composed of 45% protein, 30% fat, and 25% carbohydrates, how much energy did he expend in that day?
Explanation / Answer
Respiratory exchange ratio is the amount of carbon dioxide produced in the reaction to the amount of carbon dioxide used. Therefore, the amount of CO2 excreted at each of the three points by Lessie is calculated as follows,
At RER of 0.77, 82% of fat and 18% of carbohydrates are metabolised. At a RER of 0.83, 54% fat and 46% carbohydrates are metabolised and at a RER of 1.36, only carbohydrates are metabolised.
Lessie has 60% of the day in rest, 39% light exercise and remaining 1% maximal exertion. Since at rest, the contribution of fat to RER is more, the percentage of fat has to be increased in Lessie's diet from 30% and proteins to be decreased.
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