One of the most enduring defenses of meat eating is that we evolved to do it, and therefore must continue to do so. The claim goes that our ape and hominin ancestors were frequent, even obligatory meat eaters, and that we thus remain obligatory meat eaters. Most recently, this idea was invoked to promote yet another magical diet that would reverse weight gain and keep degenerative diseases at bay, the so-called “paleo” diet.
The argument primarily focuses on a period in our evolutionary history during which our brain expanded rapidly while our digestive system shrank, which is taken to reflect a dietary transition from plants to meat. From this, proponents suggest a causal link in which meat was the indispensable fuel that propelled the development of bigger brains during our evolutionary transition from apes to abstract analysts.
But the evidence that eating meat requires smaller digestive tracts is limited. At roughly 400 to 600 calories and 10 to 20 grams of protein per 100 grams, nuts and seeds are low-volume, high-nutritional-density foods for which small stomachs suffice. Top your greens off with peanuts and some honey, and you can do well as a plump, small-stomach, obligatory plant-eater.
Want more numerical specificity? Suppose we explore replacing modern beef with various plant-based alternatives, and calculate how much of each plant food we’d need to fully match the calories and protein in the beef. For each plant, we get two answers—one for how much plant we would need to consume to replace the energy found in serving of beef, and another for how much of the plant we would need to consume to get the protein found in a serving of beef. From these two answers, we choose the higher mass, to be sure we cover both energy and protein.
The environmental case against paleo diets is strong.
To test whether plants can match the nutritional value of meat, I compared 59 plant foods to beef. Of those, seven—almonds, kidney beans, peanuts, pistachios, chickpeas, lentils, and soy—are more protein- and energy-dense than beef, requiring consumption on average of 800 grams to replace a kilogram of beef. Six more—barley, hazelnuts, oats, walnuts, buckwheat, and spelt—are only slightly less energy- and protein-dense than beef, requiring consumption of slightly more mass (20 percent higher on average) to get the equivalent energy and protein found in beef.
The notion that our diet requires meat thus confronts roaring headwinds. While Pleistocene forebears of these nuts and legumes differed markedly from their modern counterparts, the message is clear: If more than 2 in 10 plant items are just as energy- and protein-dense as game meat, early plant-eating hominins could have invested relatively modest efforts in gathering plant-based foods to get the equivalent protein and energy found in meat, with none of the serious risks inherent in big-game hunting. This is why I find the argument that our ancestors’ brain expansion must have relied on voracious meat eating unpersuasive.
Even if our exceptional analytical skills did require meat to fuel this evolutionary upgrade, given how vastly biologically, socially, environmentally, physiologically, and nutritionally different our lives are from those of our early evolutionary forebears, how useful is this association to guide dietary choices today?
In fact, health records of 4.5 million patients show that modern meat eaters face health risks, not benefits: Increasing your unprocessed red meat consumption by 100 grams per day raises your cardiovascular risk by 5 to 16 percent, and doubling red meat intake roughly doubles the odds of death. Even if meat played a role in our evolution, therefore, its modern pervasive overconsumption comes with significant health costs.
The physiological and biochemical challenges modern diets must address and protect us from—long lives, little need for physical activity, and unlimited food supplies—clearly have little overlap with the challenges our ancestors faced: predation by larger predators, unpredictable food supply, and brief, violent lives.
Wild animal consumption is mostly irrelevant to the question at hand.
With that, let’s reexamine the paleo diet. Suppose, despite these game-changing differences, that a paleo diet is nutritionally wise for modern humans; is it deployable? I’d say not even minimally, because it is practically impossible to find meat, cereals, or greens that even vaguely resemble their paleolithic predecessors. For example, even lean farm-raised grass-fed steer or bison meat, the nearest crude modern analog to hunted Pleistocene fauna, is still 2 to 3 times fattier than wild meat and surely even more distinct in micronutrients. Likewise, how similar to their naturally occurring counterparts are, for example, manicured arugula or hyper-bred strawberries?
In my decidedly unmanicured yard, the wild strawberries are as distinct in shape, size, taste, and abundance from their grotesquely enormous modern counterparts in the supermarket as a modern confined dairy cow is from her Holocene aurochs progenitors. One proxy for this comparison is the difference between organic produce and conventionally grown counterparts, where large micronutrient differences are observed, yet likely understate the differences we are after, because modern organic produce is anything but wild. While further research is needed, the case for a paleo diet that can be reasonably characterized as promoting health in the 21st century is yet to be made. A recent effort to evaluate the paleo diet concluded that the current evidence is insufficient to recommend it even for diabetes management.
An earlier research report described the paleo diet as “an expensive and not nutritionally adequate diet with a high carbon footprint.” As to the odds of success for future efforts to corroborate the purported benefits of the paleo diet, I find it interesting that one effort was published in the journal Utopian Studies.
While the nutritional case for a paleo diet is being litigated in the scientific literature, the environmental case against paleo diets is strong, mostly because of its strong emphasis on meat, especially beef, and other animal products.
Of course, the environmental costs of paleo diets are linked to mass production of beef, and not to the kind of wild animal consumption promoted by some in the “meat is essential” camp, most compellingly and eloquently relayed by Steve Rinella, outdoorsman, author, and founder of MeatEater.
But wild animal consumption is mostly irrelevant to the question at hand, because we are interested in population statistics, not one outdoorsman’s awesome skills (which are very dear to my heart, and which Rinella beautifully and convincingly showcases). If you are unsure what distinction I am drawing here or why it matters, try recalling the last time you killed your meat, field-butchered it, carried it on your back for many miles, and cooked it over an open fire, as Rinella describes. However endearing and compelling these exploits are, they are no more relevant to population-level modern diets than Robin Hood is to modern fiscal policies. 
This article was adapted with permission from an MIT Press Reader excerpt of Planetary Eating.
Lead image: hmorena / Shutterstock
