A few related points
Quantitative environmental evaluations of meat, fresh vegetables, and processed protein based on soybeans suggest that the environmental burden of vegetarian foods is usually relatively low when production and processing are considered. The environmental comparison of cheese varieties made from cow milk and directly from lupine and the evaluation of energy inputs in fish protein and vegetable protein also suggest an environmental advantage for vegetarian food.
In the evaluation of processed protein food based on soybeans and meat protein, a variety of environmental impacts associated with primary production and processing are a factor 4.4–> 100 to the disadvantage of meat. The comparison of cheese varieties gives differences in specific environmental impacts ranging between a factor 5 and 21. And energy use for fish protein may be up to a factor 14 more than for protein of vegetable origin.
On average, 10 g of vegetable protein are needed to generate 1 g of animal protein. There are differences between different types of meat production. For broiler production, the protein conversion efficiency is about 18%, for pork about 9%, and for beef about 6%.
Assessment suggests that on average the complete life cycle environmental impact of nonvegetarian meals may be roughly a factor 1.5–2 higher than the effect of vegetarian meals in which meat has been replaced by vegetable protein.
Many scientists and even policymakers have begun to question the sustainability of agriculture as practiced today. Particular skepticism has been directed at supporting the increased demand for animal products in the diet of the economically advantaged persons of the world.