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❗Humans have unusually strong stomach acid, which proves we need to eat meat.
✅Facts:
| Feeding ecology | Mean stomach pH |
|---|---|
| Obligate scavengers | 1.3 |
| Humans | ~1.5 |
| Facultative scavengers | 1.8 |
| Generalist carnivores | 2.2 |
| Omnivores | 2.9 |
| Specialist carnivores | 3.6 |
| Hindgut herbivores | 4.1 |
| Foregut-fermenting herbivores | 6.1 |
- A healthy fasting human stomach is typically around pH 1.5–2.
- In a comparative study of 68 bird and mammal species, humans (~1.5) were closer to obligate scavengers (1.3) than to generalist carnivores (2.2) or omnivores (2.9).
- However, the researchers interpreted extreme acidity primarily as defence against foodborne pathogens, not as a meat-digestion meter.
- Rabbits and beavers also have surprisingly acidic stomachs (rabbits pH 1.0–2.0), showing that stomach pH does not uniquely identify carnivory.
- Acid activates pepsin and helps digest protein, but plant proteins require the same proteolytic machinery.
- The argument commits affirming the consequent: carnivores often have acidic stomachs, humans have acidic stomachs, therefore humans are carnivores.
- Several ecological pressures can produce an acidic stomach.
- It also confuses capacity with necessity: an acidic stomach shows humans can digest meat and cope with some pathogens, not that meat is required or optimal.
- Having lactase means someone can digest milk; it does not mean milk is physiologically necessary.
- It relies on appeal to nature: humans evolved doing X, therefore X is healthy or morally justified.
- Evolution selects for reproductive success in past environments, not longevity or modern ethics.
- It crosses the is–ought gap: even if ancestral humans hunted, that supplies no moral or nutritional rule for people with supermarkets and supplements today.
- The strongest defensible conclusion: human gastric acidity is compatible with an evolutionary history involving animal foods and pathogen exposure.
- It does not establish that animal foods are necessary, optimal, or ethically justified today.
- Appropriately planned vegan diets for adults can be nutritionally adequate and offer long-term cardiometabolic benefits, per the Academy of Nutrition and Dietetics (2025).