Brain
Starches fed the human brain. Meat did not make us smart.
19%Lower dementia risk when processed meat is replaced with legumes
It was not meat that grew the human brain. Plenty of other animals eat meat and never became human-smart. The only foods unique to humans and that make up the majority diet of humans worldwide are starches — rice, wheat, maize, potato, cassava, beans, lentils, chickpeas, etc. Humans have extra copies of starch-digesting amylase genes, and several times more salivary amylase than chimpanzees. There is no matching meat-enzyme expansion — pepsin and trypsin break down protein from any food, including plants; herbivores have them too. Without tools, cooking, and seasoning, flesh is hard and mostly bland. On one popular ranking of 30 “smartest” animals, only a handful are strict carnivores. Hardy, Brand-Miller and colleagues argue cooked starch fed the growing brain. Alzheimer’s risk tracks with processed meat. Mood studies go both ways — both sides are cited here. Brain health is not a reason to harm or eat animals.
What the evidence says
The main points first. Every claim is tied to a source below.
Alzheimer’s: meat is a risk factor; plant patterns go the other way
Adventists who ate meat were more than twice as likely to develop dementia as matched vegetarians (Giem, 1993). A 2025 Harvard/Neurology analysis found processed red meat linked with 13% higher dementia risk, and swapping that serving for nuts and legumes linked with 19% lower risk. A 2026 Neurology cohort of 92,849 people linked healthful plant-based patterns with lower Alzheimer’s and related dementias. Grant’s 2023 review names meat, saturated fat, and ultra-processed food as Alzheimer’s risk factors. Ornish 2024 reported the first randomized trial where a whole-food plant-based diet plus lifestyle changes improved or held cognition in most of the intervention group. Small trial. The direction is consistent.
Higher-IQ children were more likely to become vegetarians
Gale and colleagues followed the 1970 British birth cohort. People who were vegetarian at age 30 had scored about five IQ points higher at age 10. The direction is childhood intelligence predicting later vegetarianism, not a magic effect of beans. After accounting for social class and education, the link remains. The vegan slice of that sample was small and scored lower than other vegetarians — that detail is on the table, not buried.
It was not meat that grew the human brain
Hardy and colleagues argued that Pleistocene brain growth needed preformed glucose from cooked starch. Brand-Miller, Hardy, Copeland and others restated the case in Science in 2026: glucose from fruit and honey, then from pounded and cooked starch, was essential. Meat was eaten. It is not unique to us. Hyenas, wolves, and orcas eat meat and did not grow a 1,350-gram brain. The human specialty worldwide is rice, wheat, maize, potato, cassava, beans, lentils, chickpeas — cooked starch as the bulk of calories. FAO notes that rice, maize, and wheat alone provide about 60% of the world’s food energy. No other species made those foods the global staple.
We have extra amylase for starch. We do not have a meat-specialist gene like that.
Perry and colleagues found humans carry extra copies of the salivary amylase gene AMY1 — about three times more than chimpanzees on average, and more still in high-starch populations. Salivary amylase protein is several times higher in humans than in other great apes, often cited around six to eight fold. That is the starch adaptation. There is no matching human gene expansion for digesting raw flesh. Without tools, cooking, and seasoning, meat is hard to chew and mostly bland. The genome invested in starch. The kitchen has to do the rest for meat.
On a popular “smartest animals” list, meat-only is the minority
Sentient Media compiled a widely shared ranking of 30 animals often called most intelligent. Rankings like this are journalism, not a scientific census — they are still useful as a check on the “meat made brains” story. Of those 30, about seven eat almost only animals: dolphins, octopuses, cats, orcas, wolves, hyenas, and Portia spiders. About eleven eat almost only plants: elephants, African grey parrots, pigeons, horses, squirrels, bees, deer, llamas, koalas, gorillas, and giraffes. Chimpanzees, bonobos, and orangutans — high on the same list — live on plants for the vast majority of calories. Smart is not a carnivore club.
Mood: some studies say better, some say worse — both are here
Beezhold’s pilot trial found that dropping meat, fish, and poultry improved short-term mood. A later survey found vegans reported less stress and anxiety. Iguacel’s meta-analysis linked vegetarian and vegan diets with higher depression scores and lower anxiety. Ocklenburg also found higher depression scores. This page does not pick a mood winner. It shows the split in the evidence.
Sources
Papers and datasets. Caveats stay on the card — small samples and single animals included on purpose.
BMJ, 2007 · Observational
IQ in childhood and vegetarianism in adulthood
Gale et al., 1970 British cohort (n=8,170): vegetarians at age 30 had scored about 5 IQ points higher at age 10. The arrow runs childhood IQ → later vegetarianism, not ‘the diet made them smart.’ After class and qualifications the link remains. The vegan subsample was small and scored lower than other vegetarians — a limitation, noted here.
Quarterly Review of Biology, 2015 · Review
The importance of dietary carbohydrate in human evolution
Hardy, Brand-Miller, Brown, Thomas, Copeland: cooked starch greatly increased energy to glucose-demanding tissues, especially the brain. They argue plant starches were essential in the Pleistocene. Meat was on the menu. It was not the unique brain food. Other meat-eating animals did not evolve human-scale brains.
Science, 2026 · Review
A central role for dietary sugars in human evolution
Brand-Miller, Hardy, Copeland and colleagues, Science 2026: modelled glucose needs from four million years ago. Fruit and honey sugars first, then pounded and cooked starch once fire was in use. They conclude glucose was essential for the human brain. The bigger-brain story is carbohydrate foods as much as animal foods.
University of Sydney, 2026 · Review
Sugars may have helped fuel the human brain
University of Sydney on the 2026 Science paper: raw starch does not release glucose. Early humans likely relied on sweet plant foods before cooking made tubers and grains useful. Later, cooked starch from wild yams and similar plants contributed. Carbohydrates helped shape the brain, they argue, rather than meat alone.
FAO · Review
FAO — rice, maize, and wheat are the world’s calorie core
FAO: most people live on rice, wheat, maize, millet, sorghum, potatoes, cassava, yams. Rice, maize, and wheat provide about 60% of the world’s food energy. Those are human staple starches. They are not the staple of wolves or orcas.
Nature Genetics, 2007 · Observational
AMY1 — extra amylase copies in starch eaters
Perry et al., Nature Genetics: humans have about three times more AMY1 copies than chimpanzees, and more still in high-starch populations. That is a starch adaptation in the genome. There is no matching unique expansion for raw meat.
Physiology & Behavior, 2013 · Observational
Salivary amylase is several times higher in humans than other apes
Behringer et al. measured salivary alpha-amylase across hominoid primates. Humans show much higher levels than the other great apes — a finding that matches earlier reports putting human salivary amylase around six to eight fold higher. Dogs and some rodents later expanded amylase after eating human starch. Cats barely have it.
Sentient Media · Review
A popular ranking of 30 “smartest” animals is not a carnivore club
Sentient Media’s list of 30 animals often called most intelligent is journalism, not a lab ranking. Counted by diet: about seven are strict carnivores (dolphins, octopuses, cats, orcas, wolves, hyenas, Portia spiders). About eleven are plant specialists (elephants, African grey parrots, pigeons, horses, squirrels, bees, deer, llamas, koalas, gorillas, giraffes). Chimps, bonobos, and orangutans on the same list live mostly on plants. Meat-only does not explain smart.
FAO, food energy · Review
Cereals and tubers are the human staple, worldwide
FAO / dietary-energy accounting: rice, wheat, maize, potatoes, cassava, pulses — starch staples — supply the bulk of calories for most of the species. No other animal has a global primary diet of cooked grain and tuber.
PLOS ONE, 2015 · Review
Stomach pH 1.5 — humans and rabbits
Beasley et al.: human gastric pH ~1.5. The rabbit is the herbivore in the same dataset with a comparably acidic stomach. Authors note scavengers as a group run lowest; cats sit around 3.6. Anatomy is mixed. Stomach acid alone does not make a species a carnivore — rabbits have similar acidity.
Mills, comparative anatomy essay · Review
The comparative anatomy of eating — gut and teeth
Mills: grinding molars, no carnassial shear, a long small intestine relative to cats, a colon built to hold plant bulk. We sleep at night with the other diurnal primates. We are diurnal, like other primates, not nocturnal hunters.
Nutrition Journal, 2012 · Clinical
Meat restriction improved mood — pilot RCT
Beezhold & Johnston: omnivores randomized to drop meat, fish, and poultry improved some short-term mood scores versus controls. Small trial. Scores improved on the plant-based assignment, not the reverse.
Nutritional Neuroscience, 2015 · Observational
Vegans report less stress and anxiety
Beezhold et al., 2015: vegans reported less stress and anxiety than omnivores in this survey. Observational, not a proof of cause.
Nutrition Reviews, 2021 · Meta-analysis
Meta-analysis: vegetarian diets and higher depression scores
Iguacel et al., Nutrition Reviews: vegan/vegetarian diets associated with higher depression risk and lower anxiety. Ocklenburg 2021 similarly found higher depression scores in vegetarians. Mood findings are mixed. Both directions are listed here.
Neuroepidemiology, 1993 · Observational
Meat eaters more than twice as likely to become demented
Giem, Beeson, Fraser (Neuroepidemiology, 1993): among Adventists, matched meat-eaters (including poultry and fish) were more than twice as likely to become demented as vegetarian counterparts. Old cohort. The same direction appeared in this earlier study.
Neurology, 2025 · Observational
Processed red meat and dementia — 133,771 people
Li et al., Neurology 2025: processed red meat ≥0.25 serving/day vs <0.10, 13% higher dementia risk. Each extra daily serving, ~1.6 years faster cognitive aging. Replacing one serving with nuts and legumes: 19% lower dementia risk. Unprocessed red meat tracked subjective decline too.
Neurology, 2026 · Observational
Healthful plant-based diets and Alzheimer’s — 92,849 people
Neurology 2026: highest vs lowest plant-based diet index, 12% lower risk of Alzheimer’s and related dementias; healthful plant index 7% lower. Junk plant foods (refined grain, juice, sugar) raised risk. The benefit tracked whole plant foods, not refined ones.
J Alzheimers Dis, 2023 · Review
Diet’s role in Alzheimer’s — meat, saturated fat, junk
Grant 2023 review: identified AD risk factors include higher consumption of saturated and total fats, meat, and ultra-processed foods, and lower consumption of fruits, vegetables, legumes, nuts. The risk factors map onto common food choices.
Alzheimer’s Research & Therapy, 2024 · Clinical
First RCT: plant-based lifestyle and early Alzheimer’s
Ornish et al., Alzheimer’s Research & Therapy 2024: first randomized trial of intensive lifestyle change in MCI / early Alzheimer’s. Whole-food plant-based diet (meals delivered), exercise, stress management, group support. 20 weeks. Cognition and function improved or held in most of the intervention group; the control group mostly worsened. Small n (~51). Diet was one part of the intervention, and it was a plant-based plate.