In an article published in the september 2003 edition of The American Journal of Clinical Nutrition, David Pimentel and Marcia Pimentel examine the comparative environmental impact of the average American meat-based diet and the average American lactoovovegetarian diet (lactoovovegetarians eat dairy and eggs, but no other animal-based foods). They found that the amount of feed grain used to produce the milk and eggs in the vegetarian diet was 450 kg, while the amount of feed grain used to produce the animal products contained in the meat-based diet was almost twice that (816 kg). This explains the difference in the amount of cropland used to produce the food contained in each diet. The vegetarian diet used less than 0.4 ha of cropland, while the meat-based diet used 0.5 ha of cropland. It also explains the difference in the amount of fossil fuel required to produce the food consumed in the vegetarian diet as opposed to the meat-based diet. 25 Calories of fossil fuel are required to produce 1 Calorie of animal protein, while only 2.2 Calories of fossil fuel are needed to produce a Calorie of grain protein. 17 % of fossil fuel used in the US is used for food production.
50 % of the total land in the US is used for food production. And 90% of cropland loses soil at a rate 13 times that which is sustainable. It takes 500 years to replace one inch of lost soil, so farmers are using increasingly large amounts of commercial fertilizers in an attempt to replace lost nutrients. These fertilizers are created using large amounts of fossil fuel, and toxins from them are contaminating the local water and making their way into the ocean. And 85% of fresh water consumed in the US is used for agriculture.
Most Americans claim that they need to eat meat in order to get enough protein. The truth is that the meat based diet contains 112 g of protein per day and the vegetarian diet contains 89 g of protein per day, but the recommended daily allowance (RDA) is only 54 g of protein per day. So even without eating meat, most Americans are getting much more protein than they actually need.