I do not understand the meaning of 'calorie for calorie'.

I read an article written by Tamar Haspel and encountered a phrase that I did not understand.

' The argument that a vegetarian diet is more planet-friendly than a carnivorous one is straightforward. If we feed plants to animals, and then eat the animals, we use more resources and produce more greenhouse gases than if we simply eat the plants. As with most arguments about our food supply, though, it's not that simple. Although beef is always climatically costly, pork or chicken can be a better choice than broccoli, calorie for calorie.'

What does 'calorie for calorie' mean here? I am also not sure with the meaning of 'As with the most arguments..'

Thx in advance!