Abstract
Proton pump inhibitors strongly inhibit gastric acid production, but digestion problems do not generally arise. We can intake almost ordinary food even after total gastrectomy. Small intestine itself can digest and absorb food using various digestive enzymes without digestion in the stomach. The pH level of gastric acid in humans is much lower than that of most animals, and very close to that of carrion-eating animals called scavengers. It is assumed that ancient humans became bipedal approximately 4 million years ago. It was difficult for humans, who just started unstable bipedal locomotion, to catch quadrupedal-walking animals that can move faster, without special hunting tools. They may have eaten remaining carcasses, which is mainly the leftovers of carnivora species, as animal-derived food. The benefit to produce a volume of gastric acid for humans is carrion eating, in which disinfection by gastric acid is important. Humans produce a high concentration of gastric acid to enable consumption of a diet containing some bacteria and support this lifestyle by consuming significant energy to protect themselves from gastric acid. Now, the opportunity for strong deleterious bacteria to enter the gastrointestinal tract has decreased because of the organized clean environment. If this hygienic environment is maintained for a long time, our gastric acid level must be decreased gradually.
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