I think you’ve misunderstood the CO2 issue. The problem with greenhouse gases, the way in which they present a threat to the very existence of human civilisations, is because we are adding C/CO2 to the carbon cycle.
Growing food, eating food, metabolising food, exhaling CO2, is wholly within the carbon cycle: that is, it does not in itself add extra C/CO2 to the cycle. Some food production does add C/CO2 to the carbon cycle: fossil-fuel uses in the food supply chain, or greenhouse gas emissions from land-use changes or from livestock.
Furthermore, not only is CO2 exhaled by living creatures irrelevant to the greenhouse gas problem, but you also may have misunderstood human metabolism. Conversing uses negligible additional amounts of energy relative to standing there saying nothing, so the additional exhalation of CO2 is miniscule.
