Dear annonymous,
It is spelled "fact", not "fail".
The physiologic production of CO2 by mammals varies with the type of fuel being metabolised. The metabolism of fat produces 30% less CO2 than the metabolism of carbohydrates for the same amount of oxygen used (ie: the same metabolic rate).
An average omnivorous diet contains about 39% of its calories as fat. A lenient ovo-lacto vegetarian diet contains about 32% fat and a vegan diet, 10% fat. Given the average human daily CO2 production is about 900 grams per day* (and it is, as I measure it frequently in my line of work), it can be easily calculated that (all other things being equal) an ovo-lacto diet will produce 10kg more CO2 per year than an omnivorous diet, and a vegan diet will produce 45kg more per year.
It is, yet another, inconvenient truth.
* that's 328.5 kg/year (more on a leap year)