If you eat a variety of foods within and among groups – meat, dairy, fruit, vegetables, and grains – you don’t have to worry about nutritional details.
That’s the word from a self-styled “nutrition academic” and you might think, as I do, that that’s all you need to know. But if you’re interested in some of the details, Marion Nestle’s post Are vegetarian diets OK? is well worth spending time on. Far too sensible.
We should take this also from three other angles:
1. A large portion of agricultural land is only suitable for animal farming. One can always argue that mountain slopes can be re-forested, but I am afraid this does not facilitate skiing.
2. Most vegetarians consume dairy products. To produce milk you need cows (or goats…), and you regularly get a calf, which grows into beef.
3. Many vegetarians are also consumers of organic farming produce. Organic farming is dependent upon manure (some will challenge this) and nitrogen-fixing crops, among them fodder legumes. Cattle again comes into the picture.
Conclusion: vegetarians need meat-eaters.