[devilsbabe]

Where are they getting their "nutrients and vitamins"?

[TheSpiceIsLife]

Industrial suppliers, presumably.

Some vitamins can be created synthetically, others by modified bacteria or yeast.

I think your wider point still stands: what is the total carbon / energy / environmental foot print per food-unit equivalent.

[jquery]

If they wanted to be super green, they could use the waste products of animals.