Final answer:
The R value of 1.12 typically indicates that carbohydrate substrates are being used, as the complete oxidation of glucose has an RQ of 1.0. An RQ of 0.7 suggests fat usage, due to a lower CO2 production per O2. Carbohydrates and proteins yield about 4 kcal/g, while fats yield about 9 kcal/g for energy production.
Step-by-step explanation:
The R value, known as the respiratory quotient (RQ), represents the ratio of carbon dioxide production (CO2) to oxygen consumption (O2) in the body. When the R value is 1.12, it indicates the body is primarily using back text carbohydrate substrates, as the complete oxidation of glucose would yield an RQ of 1.0. In contrast, when the body is primarily using fat substrates, the RQ is on average about 0.7, because fat metabolism produces less CO2 for the amount of O2 consumed compared to carbohydrates.
Let's consider numerical examples of energy production from different substrates. When metabolizing glucose, a carbohydrate, the body produces approximately 4 kcal/g, similar to the expected energy yield of 17 kJ/g mentioned for carbohydrates. On the other hand, metabolizing fat can yield about 9 kcal/g and protein yields about 4 kcal/g, both values in alignment with their average fuel values of 38 kJ/g for fats and 17 kJ/g for proteins, respectively.