The human species-adapted diet contains red meat and animal fat

Any discussion about the healthfulness of specific foods must consider their place in an evolutionary, species-appropriate context. While there is no single ‘ideal’ diet for humans, it is clear that Homo evolved as a habitual meat eater, rather than merely a facultative one. In any case, veganism lacks an evolutionary precedent within the hominin lineage. 

The commonly heard activist claim that humans are naturally herbivorous, based on their phylogenetic relationship with apes, is overly simplistic. This argument focuses narrowly on the diets of shared ancestors while overlooking the evolutionary divergences that distinguish humans from other primates. Yet, even chimpanzees, our closest relatives, consume notable amounts of meat. 

Another criticism is that natural selection's focus is on fertility, not longevity. Yet, human evolution uniquely extends life beyond reproduction, supporting kin and knowledge transfer (aka 'grandmother hypothesis'). The assertion that hunter-gatherers live short lives overlooks that the data is skewed by high infant mortality, violence, and lack of modern healthcare, with survivors often living 70-80 years. 

The absence of evolutionary precedent does of course not preclude the possibility of alternative dietary approaches today. Some individuals can subsist on vegetarian diets for extended periods, but this ability is not universal. It depends on genetic variations that influence lipid metabolism, brain function, and the efficiency of converting plant-derived precursors into bioactive compounds.

Shifting to a grasslands-derived diet rich in red meat and animal fat played a transformative role in shaping human anatomy and physiology. This nutrient-dense diet fueled brain growth while enabling a reduction in the size of the energy-intensive gut. Innovations in food processing, such as cooking and fermentation, further enhanced nutrient availability by externalizing part of the digestive process.

As a result, our digestive system evolved into a compact, energy-efficient form, with an enlarged small intestine optimized for nutrient absorption and a much reduced large intestine and fermentative capacity. These adaptations were accompanied by shifts in the gut microbiota and the development of one of the most acidic stomachs among animals, likely as a defense against meat-borne pathogens.

The high energy demands of the brain further influenced body composition. Humans, particularly infants, evolved to maintain higher body fat levels than other primates, providing a crucial energy reserve. The dietary shift also resulted in smaller teeth, reduced jaw size, weaker chewing muscles, and molars optimized for meat consumption, dramatically reducing the time humans spent feeding.

The growing reliance on hunting wild animals drove a suite of anatomical adaptations that became hallmarks of the human lineage. These included endurance running, efficient heat regulation, refined breathing, specialized vision, and the ability to throw and wield tools with precision. Together, these traits enabled effective prey capture, solidifying the role of meat acquisition in human evolution.

Human metabolism is profoundly shaped by an evolutionary dependence on animal-sourced foods, particularly lipids and proteins. This dependence translated into a greater reliance on nutrients abundantly found in red meat, organ meats, and animal fat, alongside a diminished capacity to synthesize these nutrients from plant-derived precursors.

Unlike herbivores, humans preferentially absorb haem iron from meat rather than ionic iron and depend on dietary choline, which is richly supplied by animal-sourced foods. Humans have also largely lost the ability to absorb vitamin B12 from gut bacteria, synthesize taurine, or efficiently convert plant-based alpha-linolenic acid into the long-chain omega-3 fatty acids EPA and DHA.

The human brain, which consumes up to 25% of resting metabolic energy, has unique nutritional demands, particularly for DHA and arachidonic acid. Plant-based diets alone would not have provided adequate amounts of these nutrients, especially during the brain development of infants. This metabolic necessity is reflected in the human weaning process, which involves an early transition to nutrient-dense foods like meat and fat, supporting both brain development and overall growth.

• Aiello & Wheeler (1995) The expensive-tissue hypothesis: the brain and the digestive system in human and primate evolution. Current Anthropology.
• Ben-Dor et al. (2021) The evolution of the human trophic level during the Pleistocene. Yearbook of Physical Anthropology.
• Mann (2007) Meat in the human diet: An anthropological perspective. Nutrition and Dietetics - Journal of Dietiticiens Australia.
• Milton K (2003) The critical role played by animal source foods in human (Homo) evolution. The Journal of Nutrition.