A 63-year-old man with multiple rib fractures and a pulmonary contusion requires prolonged intubation. He is unable to be weaned from the ventilator and is on a volume control mode. He has a tracheostomy and a percutaneous gastrotomy in place through which he is being fed. The surgeon orders a respiratory quotient (RQ), which is the ratio of the rate of carbon dioxide production over the rate of oxygen uptake. The RQ is 1. Based on this information, which of the following is the next step in his management?