For the extra energy you can and probably would eat the lowest carbon food available which is going to be stuff like rice and pasta. You are not going to have t

For the extra energy you can and probably would eat the lowest carbon food available which is going to be stuff like rice and pasta. You are not going to have the digestive capacity to metabolize a lot of extra meat just for energy which you would tend to avoid for economic reasons. Just existing takes the majority of energy for warm blooded creatures so the percentage increase due to an increase of physical activity is relatively small. Physical activity is the cure for many medical conditions. Medical treatment has a carbon cost, probably a significant one.