Replacing meat in our diet with plant alternatives lowers the environmental costs of feeding ourselves. While backed up by voluminous and burgeoning literature, this fact is challenged by some. Some authors point out—correctly but with no clear relevance to the issue at hand, “should we eat meat, or strive to replace it with plant based alternatives”—that earlier production was even less efficient . Others incorrectly assert that grazing offers a waiver from this reality. Nonetheless, the counterarguments have gained little traction, and the environmental superiority of plant-based diets is now firmly established, held by the least conjecture-prone academic mainstream and authoritative establishment.
Yet despite mounting evidence for the safety and long term health benefits of plant based diets, nutritional objections to them persist. One popular argument often invoked to counter the resource inefficiency of livestock is that the comparison between meat- and plant-based diets is unfair—call it apples and oranges—because plants are so much less nutritious. Suggesting that its low caloric density high protein quality render meat unmatched by plants, these arguments reject the validity of hypothetical replacement diets used to demonstrate the potential effects of large-scale meat-to-plant dietary shifts.
This raises the following questions: can meat replacing, resource use optimizing plant-based diets be devised under the strict requirement that they at least match and preferably exceed the nutritional quality of the meat they replace? In a new Scientific Reports paper, we begin answering this question by devising hundreds of partial plant-based replacements to the meat portion of the mean American diet. Crucially important is that we do not design those replacement diets to globally minimize environmental costs; disregarding nutritional constraints, we could have easily doubled the environmental benefits. Minimizing environmental costs while paying close attention to nutrition is the main novelty here, our key contribution.
For that, our starting point is the assumption that divergent epidemiological outcomes of various diets are explained by a range of nutrient intake these diets span. For example, imagine two competing diets, one providing the ideal amount of a nutrient and the other providing too much. If after correcting for various confounders adherents of the two diets exhibit different aggregate health outcomes, this nutrient intake difference can be reasonably invoked to explain some of these health differences. Our numerical setup follows from this, considering simultaneously no less than 44 distinct nutrients of which the plant-based replacement diets must provide adequate or better amounts. One is equality: each plant-based replacement diet must exactly replace the protein lost by avoiding meat. The rest are inequalities (e.g., not too much saturated fat or cholesterol, not too little selenium or B12, and so on).
So, can you replace meat in the American diet with nutritionally equal or (mostly) superior plant-based alternatives?! Yes. Handily. We offer 500 such diets, and hundreds more can be easily added. With few and easily ameliorated exceptions (notably insufficient B12), these alternative diets provide (see our Fig. 1) more of desirable, protective nutrients (notably various minerals and vitamins and such phyto-nutrients as fiber, carotenes or flavonoids), and less of undesirable nutrients with known deleterious, epidemiologically adverse impacts.
What are the environmental impacts of the putative dietary switch? The nation will save about 40 million ha of high-quality cropland (as distinct from rangeland). For comparison, this saved cropland is roughly like adding four additional Iowas-worth of cropland! Some of this land may be spared. But much of it can be reallocated to producing additional fresh produce. This is of great import for a nation that currently puts nearly all its fresh produce eggs in the single basket of the Central Valley, with obvious vulnerabilities that are largely eliminated by diversifying produce sources. The switch will also free up nearly all grazed rangelands, about 260 million ha, with hard to quantify but likely considerable biodiversity benefits. Another saving involves roughly 4.5 billion kg of reactive nitrogen, the principal driver of freshwater and coastal ocean pollution. By comparison, the Mississippi river—whose N delivery to the Gulf of Mexico causes an annual Dead Zone which decimates fisheries in an area somewhere between those of Vermont and Maryland—delivers only about one billion kg. Conversely, water consumption will rise (because vegetables are mostly produced in arid parts of California while livestock feed is produced primarily in the Midwest, with little irrigation), by about 11 billion m3 or about 2% of the total national withdrawals.