I drnk coffee and occasionally have wine or spirits. I even go off the rails sometimes and eat non-zero carb food, but not very ofcten.
What do you mean "can eat this way"? I don't think I have any special physiological adaptations compared to other people.
I think it might be difficult to quantify the environmental costs of meat versus plant foods. You'd have to take into account the conditions where the food is produced (e.g. the chemicals used to control weeds, the energy spent planting and harvesting, the effect of irrigation),the amount of wastage (more than half of fruit/veg don't make it to a plate, from what I've read), the energy spent storing and shipping it it thousands of miles (in my case from California and farther), etc. My guess is that the way I eat comes out ahead as it's all local (no more than 100 miles or so) and the cattle eat mostly grass on land that is not suitable to grow anything else. You'll most likely be able to find vegan propaganda that says otherwise, though.