Evolution

The human body is built around starch

By WhyStopHarmingAnimals.com

Our genes and digestive tract carry a long record of eating plants, and starch in particular[1][2][3]. We cannot make our own vitamin C[1], our saliva starts breaking down starch before we swallow[3], and the most plausible fuel for the growing human brain was cooked carbohydrate[5]. The health of people living today points the same way.

A gene we could afford to lose

Most mammals make their own vitamin C[1]. Drouin, Godin and Page (Current Genomics, 2011) describe how anthropoid primates, humans included, along with guinea pigs and some bats, carry a broken GULO gene and cannot make ascorbic acid[1]. It has to come from food[1]. Fresh meat is a poor source, and fruit and leaves are the reliable ones[1]. A lineage can only lose that gene without harm if its diet keeps supplying the vitamin, which means a lineage that kept eating plants[1].

Digestion starts on starch

Human saliva contains amylase, the enzyme that begins breaking down starch in the mouth[3]. Perry and colleagues (Nature Genetics, 2007) found that humans carry extra copies of the salivary amylase gene, AMY1, compared with other primates[2], and that populations eating high-starch diets carry more copies still[2]. The genome shows adaptation to starch rather than to a meat-only diet[2].

Further down, Milton Mills puts the human gut at roughly ten to eleven times body length, closer to other plant-eating primates than to the short tract of a cat[3]. Stomach acid is sometimes cited as a sign of a meat eater. Beasley and colleagues (PLOS ONE, 2015) put baseline human gastric pH at about 1.5[4]. In their table, the other mammal with a stomach that acidic is the rabbit, a herbivore[4], though group averages still put scavengers lowest[4]. Stomach acidity works mainly as a filter against pathogens, and it does not mark humans as hunters[4].

What people actually eat bears this out. Lions eat meat and stay lions. Humans turned grain and roots into porridge, rice, bread and cooked tubers, and the world's staples are still starches: rice, wheat, corn, potatoes and beans.

Cooked starch and the brain

The human brain is hungry for glucose[5]. Hardy and colleagues (Quarterly Review of Biology, 2015) argue that cooked starch supplied that glucose directly[5]. Meat was eaten too, but in their analysis brain growth is less plausible without carbohydrate energy[5]. This fits Wrangham's case that cooking is a human biological trait[6]: heat makes many plant foods, too fibrous to eat raw, into usable fuel[6]. The extra AMY1 copies Perry found would have helped the body make the most of it[2].

The same body, eating today

The anatomy has a counterpart in living people. Those who eat no animals show the lowest heart-disease risk in pooled analyses, the lowest overall cancer risk in recent comparisons[8], and the lowest type 2 diabetes risk in the Adventist Health Study-2[9]. Ornish's vegetarian trial reversed coronary plaque[10], and no meat-inclusive diet has that clinical record. Li and colleagues (2025) linked processed meat with higher dementia risk[11], and an observational study found the lowest dementia risk among vegetarians of the diet groups compared[12]. Vegetarians have also come out ahead in endurance tests, including the old Yale ones.

Mental health is less settled[13][14][15][16]. A 2025 meta-analysis in Nutrition Reviews covering 709,703 adults found that the healthiest plant-based diets came with 23% lower depression risk in cohort studies[13], while unhealthy plant-based diets came with more depression and anxiety[13]. A 2021 pooling of 13 studies and 49,889 people found vegetarians scored higher on depression than non-vegetarians[14], with high heterogeneity between studies[14]. An umbrella review of the reviews found that most showed no association or conflicting results[15], and noted that reverse causation is plausible, since people who are already struggling may change how they eat[15]. A 2026 review in Frontiers in Nutrition reached a similar split: healthy plant-based patterns track with fewer depressive symptoms[16], ultra-processed plant foods with more[16], and studies of vegetarians and vegans specifically point both ways[16].

Most of this health evidence is observational, and it describes how people fare now rather than what our ancestors ate. It still lines up with the body described above: a primate that needs plants for vitamin C[1], starts digesting starch in its mouth[2][3], and does well on a plate built from them.