Animal sources are the most complete protein sources because they contain all of the amino acids we need for optimal health. The heme iron in steak is the best, most bio-available source of iron, and a small 4oz serving of beef contains 95% of the DRI for B12, something you can’t get from plants. Iron and B12 are two of the most common nutrient deﬁciencies worldwide according to the CDC.
One study in PNAS modeled what would happen if America eliminated all animal products and showed that overall caloric would increase, carbohydrate intake would increase, and nutrient deﬁciencies would increase. At the same time, greenhouse gas emissions would only reduce by 2.6%.