How Does Your Dog's Digestive System Work?

The digestive system, it’s a process that is critical for survival in all species. Digestion relies on absorption and elimination, being helped along by the gastrointestinal tract. This can only do its job properly by being in the best functioning condition.

It involves the clever biological and physiological interplay of several organs and of many enzymes and secretions. This makes the miraculous conversion of food into cellular energy.

Whilst there are many physiological similarities between a dog’s digestive system and a human’s, there’s also some key biological differences. This fact would naturally influence dietary choices for our dogs to promote optimum health.

In summary, digestion begins in the mouth using teeth to chew and create saliva before being swallowed into the oesophagus. Muscular contractions will then deliver the food particles into the stomach.

This is where digestive acids and enzymes churn the contents, breaking it all down, before reaching the small intestine. This is where most of the nutrient absorption takes place.

The small intestine contains finger-like villi that absorb nutrients that have been broken down; minerals, vitamins, amino acids, fatty acids and simple sugars. The gallbladder and the pancreas secrete enzymes for protein and carbohydrate breakdown. Finally in the large intestine waste products and water accumulate, hopefully ending up in a bio-degradable poop bag later down the line!

Interestingly, if digestion begins in the mouth, therein lies possibly the biggest difference between dogs and humans. Apart from very physically different dental structures, dogs’ being designed to slash and grab meat. Dogs have 42 teeth and compared to our 32.

A major difference is that 50% of human saliva contains salivary amylase; a protein enzyme specifically designed to rapidly alter the physical properties of starch. Dogs naturally don’t produce this starch digesting enzyme in their saliva at all!

This suggests that complex carbohydrates like rice, potatoes, sweet potatoes, legumes, and grains are more difficult, if not impossible, for dogs to digest. It indicates that people, are adept at eating starchy foods. Fun fact, humans are the only species to produce saliva amylase in such an amount. Even Chimpanzees, our closest relative produce little or none!

Adding to the important differences between dogs and humans, its notable that a dog’s stomach pH is dramatically different from ours!

Dogs are likely to produce up to 100 times the amount of acid than that of a human stomach. This means they rapidly break down proteins, having no problems softening bone matter or grizzly bits that would be impossible for a human to digest.

In contrast, the acidity of the human stomach is much similar to a herbivore’s, not a carnivore’s, supporting our ability to digest and process grains effectively. Both humans and herbivores have a mildly acidic stomach, the pH being between 4 and 5 when food is present. Carnivores, however, have a far more acidic stomach pH of 1 or less when digesting food.

Additionally, the enzyme secretion from the pancreas into the small intestine (at a critical phase of digestion) is also different. The pancreas produces three main enzymes: Amylase to break down single carbohydrates, Protease to break down proteins and Lipase (from the gall bladder) to break down fats.

Whilst dogs do produce Amylase to break down single carbohydrates, the amount of protease secreted in a canine’s pancreas is significantly higher than in a human’s. A carnivore does not secrete cellulase, unlike in a ruminant like a cow, to split cellulose into glucose molecules.

Dog’s digestive tracts are shorter than humans' at approximately two metres compared to a human’s nine metres! This difference also highlights that a carnivorous gut is predisposed to eat meat, which can be digested faster than starchy foods. This is key for a carnivore’s survival in the wild.

The health concerns around consuming overly processed, sterile, even overly cooked foods on a regular basis can result in less-than-optimal enzyme production and metabolic function overtime.

It makes sense that a sterile overly processed diet contains a deficit of appropriate enzymes. Plenty are naturally found in fresh, raw meats, offal and bone.

Sadly, the depletion of natural sources of enzymes can lead to health issues, even premature ageing. Many conditions, including, pancreatitis, diabetes, and irritable bowel disease can be attributed to a diet that a dog simply isn’t born to eat.

Recent studies on the microbiome (situated in the lining of the small intestine) relies on bacteria, both good and not so good, to thrive as an independent eco-system. This is where, science concurs, houses the immune system, and its where the clever relationship known as the gut / brain axis should flourish.

As research highlights the link between cognitive function and the digestive system, it’s time to ‘paws’ for thought and realise that dogs thrive on species-appropriate foods that are fresh and whole.

Anna Webb – as a Canine Nutrition and Behaviour expert, Anna combines her psychology degree, with study at the College of Integrated Veterinary Therapies (CIVT) and over 20 years of experience. Host of the award-nominated A DOG’S LIFE podcast, she lives in London and is owned by Prudence, a Miniature Bull Terrier, and Mr Binks, a re-homed English Toy Terrier.