What is stomach acid?

Doctors at Healthline say that human stomach acid is a watery, colourless fluid (liquid) produced by the lining of the stomach. It is also called gastric acid. 

Stomach acid helps to break down food so that it can be digested. Food that is easier to digest makes it easier for the body to absorb nutrients from the food. 

Human stomach acid has to be strong so that it can break down meat and plant-based food, such as vegetables. Scientists classify humans as omnivores because humans mainly eat both meat and vegetables.

Animals also have stomach acid to help them digest food. Animals that eat only meat have higher levels of stomach acid than animals that eat only plants and vegetation. 

Therefore, carnivores (meat-eaters), scavengers (animals that eat rotting meat and/or plant material), and omnivores (meat-and-plant-eaters) have more acid in their stomach than piscivores (fish-eaters), herbivores (plant-eaters) and frugivores (fruit-eaters). Carnivores and scavengers have higher levels of stomach acid than humans. 

Many scavengers are also carnivores. The difference is that carnivores, such as lions, hunt and kill their prey, then eat the meat, whereas scavengers usually eat animals that are already dead from natural causes or have been killed by another animal.

Vultures are scavengers. Vultures have stomach acid that is 10 times to 100 times stronger than human stomach acid. 

Scientific researchers from Washington University, North Carolina State University, and the Universtiy of Colorado, Boulder, in America wrote about their study of animal stomach acid in the journal PLOS ONE in July 2015, called “The Evolution of Stomach Acidity and its Relevance to the Human Microbiome.” They studied 68 species of birds and mammals. 

They found that scavengers have more acid in their stomach than birds and humans. They also found that stomach acidity varies within the same species due to natural causes, such as age. They found that humans who suffer from acid reflux due to high acid levels in their stomach – as high as scavengers – often need dietary changes, medicine such as antacids, or surgery to control the acid levels.

However, the researchers also found that acid enables the stomach of animals to act as a filter to control microbes that can pass through the stomach to the gut. The researchers think that high levels of stomach acid in animals did not develop to help them break down food to digest it. They think high acidity originally helped animals to defend themselves against food poisoning – because the acid can kill the bad microbes that live in their guts. 

Location of photographs: Berlin Zoo, Germany

Illustration of stomach acid: Healthline

Photographer: Martina Nicolls

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM