Carbohydrate 1.0, protein 0.8, fat 0.7, mixed diet about 0.8
Expansion
Respiratory quotient = carbon dioxide produced / oxygen consumed
| Substrate | RQ |
|---|---|
| Carbohydrate | 1.0 |
| Protein | 0.8 |
| Fat | 0.7 |
| Mixed diet | about 0.8 |
| Ketosis or starvation | may fall below 0.7 |
| Lipogenesis from overfeeding | may exceed 1.0 |
Carbohydrate has the highest value because it is already partly oxidised, so oxidising it yields a molecule of carbon dioxide for every molecule of oxygen used.
The clinical relevance is in nutritional support of a ventilated patient. Excess carbohydrate raises carbon dioxide production and therefore the ventilation required to excrete it, which can hinder weaning. Balanced feeding, avoiding overfeeding in particular, is preferable to simply reducing carbohydrate.
The measured value at the mouth is properly called the respiratory exchange ratio, which equals the tissue respiratory quotient only in a steady state; it rises above 1 during hyperventilation and heavy exercise.