The Green Lantern at Slate just addressed a question that's been bugging me for a while now. How does tofu stack up against meat for environmental impact? Soy protein is better than animal protein in most regards, but there is a whole lot of processing involved in making tofu. How does that tilt the balance?
Rastogi references a Dutch study that ranked Dutch made tofu slightly worse than Dutch raised chicken. She then takes a stab at adjusting the results for the US and decides that US tofu is probably better than chicken, but not dramatically. The change is mostly because the dutch get beans from South America.
The Dutch study is worth a look, even if the results cannot be translated directly to the US. It covers every protein source from veggie patties, to cheese, to fish and back. A quick look at the graphs (I haven't read the whole thing) revealed to surprises to me. First, cheese is horrible in this regard. Second, lamb is the worst thing ever. Which is too bad, because I wanted lamb to be a earth friendlier alternative to beef. Ah, well, I guess I'll have to live with the guilt.
Eggs, nuts, chicken, tofu, and most fish are all about the same. Milk is a slightly better and local seafood is even better than milk. Their numbers also indicate that cutting out dairy reduces greenhouse gasses as much as going meatless. That must be mostly the cheese.
Keep in mind that this is a Dutch study and the focus is greenhouse gasses. So if, like me, your concern extends to other pollutants and effects, don't treat these numbers as gospel. However, I haven't seen anything else half as useful.