Brain
Starch, not meat, fed the growing human brain
19%Lower dementia risk when processed meat is replaced with legumes
Meat didn’t grow the human brain. Cooked starches like grains and tubers likely fueled it[2][3], and humans have extra genes for digesting starch, but nothing similar for meat[6]. Starches still feed most of the world today[5]. Processed red meat is linked with more dementia[16], while healthy plant-based diets are linked with less Alzheimer’s and Parkinson’s[17][20]. If you cared about your brain, you would stop eating animals.
What the evidence says
The main points first. Every claim is tied to a source below.
Eating meat is linked with more dementia, and plant-based eating with less
In a 1993 study, Giem and colleagues found that Adventists who ate meat were more than twice as likely to develop dementia as matched vegetarians[1], and later research found vegetarian diets had the lowest dementia risk of the diet groups compared[2]. A 2025 Harvard analysis in Neurology linked processed red meat with 13% higher dementia risk, and swapping that serving for nuts and legumes with 19% lower risk[3]. A 2026 Neurology study of 92,849 people linked healthy plant-based eating with lower rates of Alzheimer’s and related dementias[4], and Grant’s 2023 review names meat, saturated fat, and ultra-processed food as risk factors for Alzheimer’s[6]. In 2024, Ornish reported the first randomized trial in which a whole-food plant-based diet plus lifestyle changes improved cognition or kept it stable in most of the people on the program[5]. The trial was small[5], but its results fit with the other studies.
Read full article →Children with higher IQs were more likely to grow up vegetarian
Gale and colleagues followed the 1970 British birth cohort[1]. People who were vegetarian at 30 had scored about five IQ points higher at age 10, so the higher IQ came first and the vegetarianism later; beans didn’t raise anyone’s IQ[1]. The link held after accounting for social class and education[1]. Only a small number were vegan, and they scored lower than the other vegetarians[1].
Read full article →Our big brains grew on glucose from starch and fruit, not on meat
Hardy and colleagues argued that brain growth in the Pleistocene needed ready-made glucose from cooked starch[1]. In Science in 2026, Brand-Miller, Hardy, Copeland, and others made the case again: glucose from fruit and honey, and later from pounded and cooked starch, was essential[2]. Our ancestors did eat meat[1], but so do hyenas, wolves, and orcas, and none of them grew a 1,350-gram brain. What sets humans apart is that cooked starch makes up the bulk of our calories worldwide: rice, wheat, maize, potato, and cassava[4], plus beans, lentils, and chickpeas. According to the FAO, rice, maize, and wheat alone provide about 60% of the world’s food energy, and no other species has made foods like these its global staple[4].
Read full article →Humans evolved extra copies of a starch-digesting gene, and nothing similar for meat
Perry and colleagues found that humans carry extra copies of AMY1, the gene for salivary amylase: about three times as many as chimpanzees on average, about six to eight times as much of the protein, and more copies still in populations that eat a lot of starch[1]. Those extra copies are how we adapted to starch[1], and humans have nothing comparable for digesting raw flesh. Behringer and colleagues measured the enzyme in bonobos, chimpanzees, gorillas, and orangutans, not in humans, and found higher levels in gorillas and orangutans[2]. Without tools, cooking, and seasoning, meat is hard to chew and mostly bland[3], so it took a kitchen to make it edible.
Read full article →Plant-eaters outnumber meat-eaters on a popular list of the smartest animals
Sentient Media put together a widely shared list of 30 animals often called the most intelligent[1]. It’s journalism, not a scientific census, but it’s still a useful check on the claim that eating meat is what made brains big[1]. About seven of the 30 eat almost only animals: dolphins, octopuses, cats, orcas, wolves, hyenas, and Portia spiders[1]. About eleven eat almost only plants: elephants, African grey parrots, pigeons, horses, squirrels, bees, deer, llamas, koalas, gorillas, and giraffes[1]. Chimpanzees, bonobos, and orangutans, also high on the list, get the vast majority of their calories from plants[3].
Read full article →Studies disagree on whether plant-based eating helps mood
Some studies found a benefit. In Beezhold’s pilot trial, giving up all animal flesh, fish included, improved short-term mood[1], and a later survey found vegans reported less stress and anxiety[2]. In an 18-week workplace vegan trial, depression, anxiety, and work-productivity scores all improved[6], and across 709,703 adults, the healthiest plant-based diets were linked with 23% lower depression risk, while unhealthy ones were linked with more depression and anxiety[3]. Other studies found the opposite or nothing: when 13 studies of 49,889 people were pooled, vegetarians scored higher on depression, though results varied widely between studies[4]. A 2022 meta-analysis of vegetarian eating found no significant link with depression, anxiety, or stress[7], and an umbrella review found that most reviews showed no link or mixed results, and that people may change their diet because they’re depressed rather than the reverse[5].
Read full article →People on the healthiest plant-based diets had 22% lower Parkinson’s risk
UK Biobank researchers followed people for 11.8 years and recorded 577 new cases of Parkinson’s[1]. Those eating the healthiest plant-based diets had 22% lower risk, and those eating unhealthy plant-based diets had 38% higher risk[1]. Vegetables, nuts, and tea were each linked with 25–31% lower risk on their own[1]. The link held in people without a high genetic risk score[1], but not in those with one. In a separate study, three or more daily servings of low-fat dairy came with 34% higher Parkinson’s risk than none, mostly from skim and low-fat milk, though total dairy on its own wasn’t significant[2].
Read full article →Articles
Cooked starch fueled the growth of the human brain
Humans evolved extra copies of a starch-digesting gene, with nothing like it for meat, and most people on Earth live on grains, tubers and pulses. Researchers who study human evolution argue that glucose from plants, especially cooked starch, fueled the brain as it grew.
Read full article →
Plant-based diets are linked with less dementia and Parkinson’s
In large studies, processed meat is linked with more dementia and healthy plant-based diets with less dementia and Parkinson’s, and in the first small trial of a whole-food plant-based program, most people with early cognitive decline held steady or improved. Studies on diet and mood disagree.
Read full article →
Sources
Papers and datasets. Each card keeps its caveats, including small samples and single-animal cases.
[1]BMJ, 2007 · Observational
Kids with higher IQs were more likely to go vegetarian as adults
Gale and colleagues looked at 8,170 people in the 1970 British cohort and found that those who were vegetarian at age 30 had scored about 5 IQ points higher at age 10. Childhood IQ came first, so this doesn’t show “the diet made them smart,” though the link remained after adjusting for social class and qualifications. The vegan subgroup was small and scored lower than the other vegetarians.
[2]Quarterly Review of Biology, 2015 · Review
Cooked starch greatly increased the energy available to the human brain
Hardy, Brand-Miller, Brown, Thomas, and Copeland argue that cooked starch greatly increased the energy reaching tissues that need glucose, especially the brain, and that plant starches were essential during the Pleistocene. Meat was on the menu, but it wasn’t a unique brain food, and other meat-eating animals didn’t evolve brains like ours.
[3]Science, 2026 · Review
Fruit, honey, and later cooked starch fueled the human brain
Brand-Miller, Hardy, Copeland, and colleagues (Science, 2026) modeled human glucose needs going back four million years. Sugars from fruit and honey came first, then pounded and cooked starch once people used fire. They conclude glucose was essential for the human brain, so carbohydrate foods matter as much as animal foods in explaining how our brains got bigger.
[4]University of Sydney, 2026 · Review
Sugars may have helped fuel the human brain
The University of Sydney’s write-up of the 2026 Science paper explains that raw starch doesn’t release glucose, so early humans likely relied on sweet plant foods before cooking made tubers and grains useful. Later, cooked starch from wild yams and similar plants added to that. The researchers argue that carbohydrates, not meat alone, helped shape the brain.
[5]FAO · Review
Rice, maize, and wheat give the world about 60% of its food energy, says the FAO
The UN Food and Agriculture Organization says most people live on rice, wheat, maize, millet, sorghum, potatoes, cassava, and yams, and that rice, maize, and wheat alone provide about 60% of the world’s food energy. These starchy staples are human foods, and no wolf or orca lives on them.
[6]Nature Genetics, 2007 · Observational
Humans have about three times as many starch-digesting gene copies as chimps
Perry and colleagues (Nature Genetics) found that humans have about three times as many copies of AMY1, the starch-digesting gene, as chimpanzees, and about six to eight times as much salivary amylase protein. People from high-starch populations have more copies still. It’s an adaptation to starch, and there’s no similar gene expansion for eating raw meat.
[7]PLOS ONE, 2013 · Observational
Gorillas and orangutans had more salivary amylase than chimpanzees and bonobos
Behringer and colleagues measured salivary alpha-amylase in bonobos, chimpanzees, gorillas, and orangutans, not in humans. Gorillas and orangutans had higher baseline levels than the chimpanzees and bonobos. The paper does not say humans have six to eight times more, and it does not mention dogs, rodents, or cats.
[8]Sentient Media · Review
Only about seven of the 30 “smartest” animals on a popular list are strict carnivores
Sentient Media’s list of 30 animals often called the most intelligent is journalism rather than a lab ranking. Sorted by diet, about seven are strict carnivores (dolphins, octopuses, cats, orcas, wolves, hyenas, and Portia spiders), about eleven are plant specialists (elephants, African grey parrots, pigeons, horses, squirrels, bees, deer, llamas, koalas, gorillas, and giraffes), and chimps, bonobos, and orangutans live mostly on plants. So a meat-only diet doesn’t explain intelligence.
[9]FAO, food energy · Review
Grains and tubers supply most of the calories people eat worldwide
According to the FAO’s figures on dietary energy, starchy staples such as rice, wheat, maize, potatoes, cassava, and pulses supply most of the calories for most of humanity. No other animal species lives mainly on cooked grains and tubers.
[10]PLOS ONE, 2015 · Review
Human stomachs are about as acidic as a rabbit’s, around pH 1.5
Beasley’s team put human stomach pH at about 1.5, and in their dataset the rabbit, a herbivore, has a comparably acidic stomach. Scavengers as a group have the most acidic stomachs, and cats are around 3.6. Human anatomy has mixed features, and stomach acid alone doesn’t make a species a carnivore.
[11]Mills, comparative anatomy essay · Review
Human teeth and guts are built for plants, Milton Mills argues
Milton Mills points to our grinding molars, our lack of the carnassial teeth that carnivores use to shear meat, a small intestine that is long compared with a cat’s, and a colon built to hold bulky plant food. Like the other primates that are active by day, we sleep at night, and we aren’t nocturnal hunters.
[12]Nutrition Journal, 2012 · Clinical
Cutting out meat and fish improved mood in a small pilot trial
Beezhold and Johnston randomly assigned meat-eaters to stop eating all animal flesh, fish included, and that group improved on some short-term mood scores compared with controls. It was a small trial.
[13]Nutritional Neuroscience, 2015 · Observational
Vegans reported less stress and anxiety than omnivores
In a 2015 survey by Beezhold and colleagues, vegans reported less stress and anxiety than omnivores. It’s an observational study, so it can’t prove the diet caused the difference.
[14]Nutrition Reviews, 2021 · Meta-analysis
A meta-analysis linked vegetarian diets with more depression but less anxiety
In a meta-analysis, Iguacel and colleagues linked vegan and vegetarian diets with a higher risk of depression and with lower anxiety. A 2021 paper by Ocklenburg also found higher depression scores in vegetarians, so the research on diet and mood is mixed.
[15]Neuroepidemiology, 1993 · Observational
Adventists who ate meat were more than twice as likely to develop dementia
Giem, Beeson, and Fraser compared matched Adventists and found that the meat-eaters, including those who ate chickens, turkeys, and fish, were more than twice as likely to develop dementia as the vegetarians. It’s an old cohort, but newer studies have found the same link.
[16]Neurology, 2025 · Observational
Processed red meat came with 13% higher dementia risk in 133,771 people
Li and colleagues followed 133,771 people. Eating at least 0.25 servings of processed red meat a day, compared with less than 0.10, came with 13% higher dementia risk, and each extra daily serving with about 1.6 years of faster cognitive aging. Swapping one serving for nuts and legumes was linked with 19% lower dementia risk, and unprocessed red meat was linked with self-reported cognitive decline too.
[17]Neurology, 2026 · Observational
Plant-based eating came with 12% lower Alzheimer’s risk in 92,849 people
In a 2026 Neurology study of 92,849 people, those with the highest plant-based diet index scores had 12% lower risk of Alzheimer’s and related dementias than those with the lowest, and the healthful plant-based index showed 7% lower risk. Junk plant foods like refined grains, juice, and sugar raised the risk, so the benefit came from whole plant foods.
[18]J Alzheimers Dis, 2023 · Review
Meat, saturated fat, and ultra-processed food are risk factors for Alzheimer’s
Grant’s 2023 review found that the dietary risk factors for Alzheimer’s disease are everyday food choices: eating more saturated fat, total fat, meat, and ultra-processed food, and fewer fruits, vegetables, legumes, and nuts.
[19]Alzheimer’s Research & Therapy, 2024 · Clinical
Most people with early Alzheimer’s held steady or improved on Ornish’s plant-based program
Ornish and colleagues ran the first randomized trial of intensive lifestyle change for mild cognitive impairment or early Alzheimer’s, with 20 weeks of a whole-food plant-based diet (meals delivered), exercise, stress management, and group support. Cognition and function improved or held steady in most of the intervention group, while most of the control group got worse. The trial was small (about 51 people), and diet was only one part of the program.
[20]Movement Disorders, 2023 · Observational
The healthiest plant-based diets came with 22% lower Parkinson’s risk
UK Biobank researchers followed people for 11.8 years and recorded 577 new cases of Parkinson’s. The healthiest plant-based eating came with 22% lower risk, and unhealthy plant-based eating with 38% higher risk. Vegetables, nuts, and tea were each linked with 25–31% lower risk on their own, and the link showed up even in people without a high genetic risk score.
[21]Neurology, 2017 · Observational
Three or more servings of low-fat dairy a day came with 34% higher Parkinson’s risk
In two long-running cohorts, people who had three or more servings of low-fat dairy a day had 34% higher risk of Parkinson’s than people who had none, mostly because of skim and low-fat milk. Total dairy on its own wasn’t significantly linked.
[22]American Journal of Health Promotion, 2015 · Clinical
Eighteen weeks of a vegan diet improved mood and productivity at work
At ten corporate sites, 292 employees were randomly assigned to 18 weeks of weekly vegan-diet classes or to no change. The people in the diet group improved on depression, anxiety, and work-productivity scores.
[23]Critical Reviews in Food Science and Nutrition, 2022 · Meta-analysis
A meta-analysis found no significant link between vegetarian diets and depression
Pooling the observational studies, researchers found no significant link between vegetarian eating and depression, anxiety, or stress. Studies of diet and mood have found results in both directions.