Respiratory quotient on a mixed diet is:

The respiratory quotient (RQ)is the ratio in the steady state of the volume of CO2 produced to the volume of O2 consumed per unit of time. The RQ of carbohydrate is 1.00, and that of fat is about 0.70. This is because H and O are present in carbohydrate in the same propoions as in water, whereas in the various fats, extra O2 is necessary for the formation of H2O. A mixed diet of fat and carbohydrate results in an average value between these numbers. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 26. Digestion, Absorption, & Nutritional Principles. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.