Humans were mostly on an animal based diet for more than two millions years
In 2021 a remarkable study was published called “The evolution of the human trophic level during the Pleistocene”, link below. It is remarkable not because it concludes that contrary to the widespread hypothesis that humans owe their evolution and survival to their dietary flexibility, which allowed them to combine the hunting of animals with vegetable foods, the picture emerging here is of humans evolving mostly as predators of large animals - this we as Paleo followers already knew. It is remarkable because of the depth and rigor of research the authors took upon to come to this conclusion. Dr. Ben-Dor and his colleagues collected about 25 evidences from about 400 scientific papers from different scientific disciplines including human physiology and genetics, archaeology, paleontology, and zoology. And all evidence points to the fact that the only reason why humans increased eating vegetables is because there were too few animals left for hunting.
Let’s dive deeper into this study and the evidence:
1. BIOENERGETICS
Compared with other primates, humans had required higher energy for a given body mass in a shorter time during the day therefore; they needed to obtain adequate and consistent energy to energize themselves, especially to reliably energize the brain. Thus, animal-sourced food was more efficient to their need as it returned tens of thousands of calories per hour and was more time-efficient than plant-gathering. This indicated the specialized hunting skills of humans and indicated them as predators.
2. DIET QUALITY
In primates, a larger brain is associated with high energy density food. Human brains were over three times larger than other primates' brains. With the largest brain among primates, humans are likely to have targeted the highest density food which is animal fats first, and animal proteins second.
3. HIGHER FAT RESERVES
With much higher body fat reserves than primates, humans are uniquely adapted to lengthy fasting. Fat reserves may have evolved to allow extended fasting of several weeks, thereby bridging a variable encountering rate with large prey. This adaptation may have helped with overcoming the erratic encountering of large prey. Further, they had adapted to efficiently synthesize ketones to replace glucose as an energy source for the brain during fasting.
4. GENETIC AND METABOLIC ADAPTATION TO A HIGH-FAT DIET
Humans adapted to higher fat diets, presumably from animals which suggest that humans shut down regions of the genome to accommodate a high-fat diet. It is hypothesized that humans eating an animal-based diet would display an obligatory requirement for significant fat amounts because they are limited in the amount of protein they can metabolize to energy.
5. TARGETING FAT
Humans targeted animal fat by hunting large and prime-adult animals, both of which have a higher fat level, by bringing fatty parts to central places and exploiting bone fats at a great energetic expense. The recognition of targeting fat as a driver of human behavior supports the importance of large, higher fat-bearing animals to humans’ survival.
6. STOMACH ACIDITY
Higher stomach acidity is found in carnivores to fight meat-borne pathogens. Humans' stomach acidity is even higher than in many other carnivores. The acidity in our stomach is high when compared to omnivores and even to other predators. Producing and maintaining strong acidity require large amounts of energy, and its existence is evidence for consuming animal products.
7. GUT MORPHOLOGY
Humans' gut morphology and relative size are radically different from chimpanzees' guts. Longer small intestines and shorter large intestines are typical of carnivores' gut morphology and limit humans' ability to extract energy from plants' fiber.
8. INSULIN RESISTANCE
Humans, like carnivores, have a low physiological (non-pathological) insulin sensitivity. It allows prioritizing of glucose toward tissues like the central nervous system that entirely or significantly depend on glucose, rather than muscles which can rely on fatty acids and ketosis instead.
9. VITAMINS
Comparison of vitamin density (per 100 calories) between terrestrial mammals and plants shows that, in eight of the ten vitamins, terrestrial mammal food is denser, and in most cases several times denser, than plants. If one considers factors like bioavailability and active nutrients, then animal foods appear even more nutritious.
Higher requirements for vitamin C in western populations may result from higher consumption of carbohydrates and consequently higher blood glucose levels. Animal foods also provide generous amounts of carnitine, meaning that less vitamin C is needed to synthesize carnitine. Animal-sourced foods provide essential micronutrients in their active forms that plants do not, such as vitamin A (retinol), vitamin K (K2 menaquinones), vitamin B9 (folate), vitamin B12 (cobalamin), vitamin B6 (pyridoxine), vitamin D (cholecalciferol), iron (heme iron), and omega-3 (EPA and DHA).
Hence, it appears that all vitamins, including vitamin C, are supplied in adequate quantities on a carnivorous diet.
Summary
Humans were hyper-carnivores, meaning at least 70% of their diet was derived from animals.
Source
“The evolution of the human trophic level during the Pleistocene”, by Miki Ben-Dor, Raphael Sirtoli, Ran Barkai, https://onlinelibrary.wiley.com/doi/10.1002/ajpa.24247
