An "ecological footprint" is a metaphor used to predict the amount of land a human population would hypothetically need to provide the resources required to support itself and to absorb its wastes. It compares human consumption of natural resources with the earth's ecological capacity to regenerate them. (Human footprint has currently exceeded the sustainable bio-capacity of the planet by 25%)

Footprinting is widely used as an indicator of the environmental sustainability of individual lifestyles, industry sectors, regions, and nations. For an average citizen in the UK, for example, living an environmentally friendly lifestyle in a not too big house you get the following figures:

According to www.ecologicalfootprint.com she will have a footprint of 4.4 hectares/year if she is an average meat eater and 4.9 if she is a heavy meat consumer, but she needs only 3.6 hectares/year if she is a vegetarian and 3.3 if she is vegan (no meat or dairy products at all). For other Western European countries these numbers would be very much the same.

At this moment, there are about 1.65 hectares available per person.

If everyone in the world would try to adapt to the UK lifestyle, we would need 2.7 planets for the regular meat eater, 3 planets for the heavy meat eater, 2.2 for a vegetarian and 2 for the vegan.

While there is much discussion about the methodology of ecological footprints it is still a useful tool to point at huge differences a change in lifestyle can have.
Going vegan saves you a planet. The nearest next one is about 20 light years away...

The figures also show that we need to change more than our food consumption. Think reducing use of energy, changing travelling patterns, lowering your standards. Or we will need to reach planets much much further away...

source:
www.ecologicalfootprint.com