Throughout nearly all of human evolutionary history, there were no nutritionists, no food labels, and no dietary guidelines. Like every other animal, we ate according to our biology, guided exclusively by our evolutionary instincts. Today we are somehow the only species on the planet that doesn’t know what to eat. We are surrounded by thousands of foods and food products that didn’t exist for the majority of our evolutionary past and a corresponding epidemic of chronic diseases. The ancestral dietary framework aims to correct this by returning to the most fundamental and well-tested nutritional blueprint in human history.
What Our Ancestors Really Ate
The best evidence for what our ancestors ate is from paleo-anthropology, specifically by looking at the archaeological record and bones of our ancestors.
Archeological sites of pre-humans dating to approximately 2.6 million years ago demonstrate stone tools used to cut flesh and crack open bones to extract the bone marrow [1]. Around 2 million years ago, early humans were systematically acquiring and processing numerous complete animal carcasses. This pattern appears consistently across various sites spanning hundreds of thousands of years and multiple continents, indicating that animal consumption was a large part of the ancient human diet [2].
The evidence for large-scale animal consumption is further backed up by modern chemical paleo-anthropology techniques, which measure specific ratios of nitrogen isotopes from the collagen of the long bone of ancient human remains, and places these organisms at different trophic levels, meaning where they lie on the food chain. Human remains constantly produced values as high as, or even higher than hyper carnivores like lions wolves and hyenas [3][4]. Humans were apex predators and at the vary top of the food chain, and animal foods were the primary source of dietary protein for the human diet across our evolutionary history.
There is also evidence of some plant foods consumed as part of the ancestral diet, although the direct evidence is somewhat limited. Dental calculus suggests that some amount of plant material was consumed, although this does not give us an estimate about the proportions eaten [5]. There is also no archaeological evidence of the organized, systematic procurement of plant foods in the same way that there is with animal foods, with no documented specialized processing tools or storage mechanisms. This type of systematic plant food processing only begins to appear around 30,000 years ago, corresponding to the time when humans began hunting large megafauna to extinction [6]. This suggests that increased plant consumption may have been a compensatory adaptation to the loss of the large fatty animals that had long formed the backbone of the human diet. It’s also worth noting that the plants consumed were the plants seasonally available, predominantly fibrous tubers, nuts, fruits and wild seeds. Not the cultivated grains and starches that dominate the modern diet.
The Biological Footprint: What our Bodies are Adapted to Eat
Paleo-anthropology describes what our ancestors were most likely eating, but our own biology describes exactly what modern humans are best adapted to eat.
The strongest piece of evidence lies on our stomach acidity. A systematic review across 68 species found that scavengers and carnivores have significantly higher stomach acidities as measured on the pH scale [7]. It’s important to note that each one point lower on the pH scale corresponds to being 10x more acidic.
Human stomach acidity sits at a pH of around 1.5, more acidic than most generalist carnivores and even closer to scavengers than omnivores, really challenging the conventional human classification as omnivores [7]. Maintaining this level of acidity is expensive, requiring significant nutrient and energy demands. The fact that our body deems this necessary points to a long evolutionary history of consuming animal foods, where a very acidic stomach serves to break down dense animal proteins, as well as defend against pathogenic micro-organisms in meat.
Our gut structure tells a similar story. Herbivores contain a large cecum, a highly developed fermentation chamber, housing the bacteria needed to break down indigestible cellulose from plant matter. The human cecum is a dramatically reduce remnant of the much larger herbivorous cecum found in our primate ancestors, having lost its primary function of cellulose fermentation over the course of human evolution [8]. This is not the gut of an animal designed to subsist primarily on plant matter.
These adaptations make perfect sense when framed through the lens of the expensive tissue hypothesis. The human brain is the most metabolically expensive organ in the body, consuming about 20% of our energy despite only comprising 2% of our body mass. The gut is similarly expensive. Maintaining the large fermentation chambers needed to extract nutrition from plant matter requires enormous metabolic investment. The hypothesis proposes that consuming primarily nutrient dense fatty animal foods removed the need for a large, costly digestive system. As the gut shrank, the energy was freed up and was redirected toward expanding the brain [9]. We traded fermentation capacity for the very brains that made us human, a processed fuelled by the consumption of animal foods.
A counterargument often raised against humans primarily consuming animals is that we lack the sharp pointy teeth of dedicated predators, with our teeth instead resembling those of frugivores. This is true, but largely irrelevant, as humans have used tools to process food for the last 2.6 million years as demonstrated in the archaeological record. A species that butchers, cooks and processes its food mechanically does not require teeth to tear raw flesh from a carcass, and there would have been no evolutionary selective pressure towards this adaptation. Our stomach, our gut, and our metabolic machinery are far more informative guides to what we are designed to eat than the shape of our teeth.
Nutrient Density and Bioavailability
Animal foods offer nutrients in their most bioavailable form. The amino acids, fatty acids, vitamins and minerals derived from animal sources are structured in ways and exist in ratios that human physiology is primed to absorb and utilize efficiently [10][11]. Plant foods often contain the same nutrients in imbalanced ratios, or in precursor/bound forms that the body must convert into the active usable form . This conversion process is often very inefficient and can have meaningful implications for energy metabolism, hormonal health, and brain function [10][11].
Many plant foods often contain compounds called anti-nutrients that actively interfere with digestion, block the absorption of key minerals, or directly damage the gut. This is an evolutionary defence mechanism that plants evolved in order to discourage predation and proliferate[12]. What matters is understanding that plants exist on a spectrum of toxicity, from broadly benign to genuinely problematic. It’s also important to note that the plants our ancestors consumed were eaten seasonally, in limited quantities, and were prepared using traditional techniques like fermentation, soaking, and cooking that significantly reduces their anti-nutrient load [12]. This is in stark contrast to the modern diet in which problematic plant compounds are consumed year-round, in concentrated forms, with little of the preparation techniques that made them safer and more nutritious to eat.
Both nutrient bioavailability and the spectrum of plant toxicity are important subjects to understand and I plan on covering these topics in more depth in future posts.
Putting it All Together
For the vast majority of human evolution, fatty animal meat formed the nutritional backbone of the human diet. Plants were part of the picture, consumed locally, seasonally, and in forms our ancestors knew how to prepare, but these were supplementary rather than foundational. The modern diet has inverted this relationship entirely, building its foundation on cultivated grains, refined starches, industrial seed oils, and processed foods that have no meaningful presence in our evolutionary history.
The ancestral dietary framework is not a rigid dietary protocol, it is a framework built on a simple principle: prioritize eating the foods that humans have always eaten and that our bodies are most adapted to utilize. In practice, this means making animal foods the centre of your plate and the focus of every meal. Plant foods can definitely be a part of your ancestrally consistent diet, but they should be considered supplementary to meat-based foods, with an emphasis on local, seasonal options that are chosen and prepared with an awareness of their toxin load.
Ultimately, the ancestral dietary framework is a starting point, not a finish line. The evidence broadly establishes what our bodies were built to run on, but individual variation is real. Differences in genetics, microbiota, lifestyle and health history means that no universal protocol works perfectly for everyone. The framework gives you the most evidence based foundation to start from. Use these principles and experiment: try different macronutrient ratios, different ratios of animal to plant foods, different food preparation techniques. Pay attention to how your body responds, adjust accordingly, and over time you will build a nutritional protocol that is not just ancestrally consistent but genuinely tailored to you.
References
- Semaw S, Rogers MJ, Quade J, et al. 2.6-million-year-old stone tools and associated bones from OGS-6 and OGS-7, Gona, Afar, Ethiopia. J Hum Evol. 2003;45(2):169–177. Available from: https://www.sciencedirect.com/science/article/abs/pii/S0047248403000939
- Ferraro JV, Plummer TW, Pobiner BL, et al. Earliest archaeological evidence of persistent hominin carnivory. PLoS ONE.2013;8(4):e62174. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC3636145/
- Richards MP, Trinkaus E. Isotopic evidence for the diets of European Neanderthals and early modern humans. Proc Natl Acad Sci USA. 2009;106(38):16034–16039. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC2752538/
- Bocherens H, Worthington SR, Jaouen K. Neanderthals, hypercarnivores, and maggots: Insights from stable nitrogen isotopes. Sci Adv. 2024. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC12292906/
- Henry AG, Brooks AS, Piperno DR. Microfossils in calculus demonstrate consumption of plants and cooked foods in Neanderthal diets. Proc Natl Acad Sci USA. 2011;108(2):486–491. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC3021051/
- Revedin A, Aranguren B, Becattini R, et al. Thirty thousand-year-old evidence of plant food processing. Proc Natl Acad Sci USA. 2010;107(44):18815–18819. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC2973873/
- Beasley DE, Koltz AM, Lambert JE, Fierer N, Dunn RR. The evolution of stomach acidity and its relevance to the human microbiome. PLoS ONE. 2015;10(7):e0134116. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC4519257/
- Chivers DJ, Hladik CM. Morphology of the gastrointestinal tract in primates: comparisons with other mammals in relation to diet. J Morphol. 1980;166(3):337–386. Available from: https://pubmed.ncbi.nlm.nih.gov/7441763/
- Aiello LC, Wheeler P. The expensive-tissue hypothesis: The brain and the digestive system in human and primate evolution. Curr Anthropol. 1995;36(2):199–221. Available from: https://www.scielo.br/j/bjg/a/FxXZ7LPBDmZxjKKVbPym4Vb/
- Chungchunlam SMS, Moughan PJ. Comparative bioavailability of vitamins in human foods sourced from animals and plants. Crit Rev Food Sci Nutr. 2023. Available from: https://pubmed.ncbi.nlm.nih.gov/37522617/
- Gibbs J, Cappelle K, Llort KF, et al. Friend or foe? The role of animal-source foods in healthy and environmentally sustainable diets. J Nutr. 2022;152(Suppl 1):1S–15S. Available from: https://www.sciencedirect.com/science/article/pii/S0022316622131378
- López-Moreno M, Garcés-Rimón M, Miguel M. Anti-nutrients: Lectins, goitrogens, phytates and oxalates, friends or foe? J Funct Foods. 2022;89:104938. Available from: https://www.sciencedirect.com/science/article/pii/S1756464622000081