No, it wouldn't.
Look at pandas, they are bears (omnivores, like us), living on a primarily vegetarian diet.
They sleep 16 hours a day and when they are awake they eat, because a vegetarian diet is not really energy efficient.
If we are talking about a true vegetarian diet, environmental friendly.
if we are talking about "I can be mostly vegetarian because I buy integrators from the drugstore" that's the same of eating fried chicken intensively farmed 4 times a day, in large quantities, for the environment.
What most western cultures should aim for is eating raw food, completely avoid processed food and, most of all, EAT LESS.