Which statement about RQ and interpretation is true?

Which statement about RQ and interpretation is true?

• A. RQ of 0.85 indicates mixed substrate utilization or appropriate nutrient delivery
• B. RQ of 0.85 indicates pure carbohydrate oxidation
• C. RQ of 0.85 indicates overfeeding
• D. RQ of 0.85 indicates protein oxidation

Answer: (A)

RQ reflects which substrates the body is oxidizing for energy. It’s the ratio of CO2 produced to O2 consumed, and it helps infer whether carbohydrates, fats, or proteins are being used. Carbohydrate oxidation drives RQ toward about 1.0, fat oxidation drives it toward about 0.70, and protein oxidation is around 0.80. An RQ of 0.85 sits between fat and carbohydrate, indicating mixed substrate utilization. In clinical nutrition, this pattern often corresponds to balanced substrate oxidation when energy delivery is appropriate—neither exclusively carbohydrate nor exclusively fat nor protein. It’s not a sign of pure carbohydrate oxidation (that would be closer to 1.0) or pure protein oxidation (about 0.80). While very high RQ can accompany overfeeding (more carbohydrate oxidation), 0.85 best warrants the interpretation of mixed substrate use or adequate nutrient delivery.

RQ reflects which substrates the body is oxidizing for energy. It’s the ratio of CO2 produced to O2 consumed, and it helps infer whether carbohydrates, fats, or proteins are being used.

Carbohydrate oxidation drives RQ toward about 1.0, fat oxidation drives it toward about 0.70, and protein oxidation is around 0.80. An RQ of 0.85 sits between fat and carbohydrate, indicating mixed substrate utilization. In clinical nutrition, this pattern often corresponds to balanced substrate oxidation when energy delivery is appropriate—neither exclusively carbohydrate nor exclusively fat nor protein. It’s not a sign of pure carbohydrate oxidation (that would be closer to 1.0) or pure protein oxidation (about 0.80). While very high RQ can accompany overfeeding (more carbohydrate oxidation), 0.85 best warrants the interpretation of mixed substrate use or adequate nutrient delivery.