There are many differences in the digestion of fresh, raw food versus dry, extruded food. Many of these differences are some of the main reasons why raw diets can be superior to kibble. Minimally processed, animal based proteins are highly digestible and provide optimal amounts of a wide variety of amino acids, which are then used for almost every metabolic function in the body. Antinutrients that can interfere with the absorption of vitamins and minerals are not a worry in low- or no-carbohydrate diets. Raw diets have been shown to promote healthier gut flora than dry food, improving digestion and overall health.
There are two main reasons why owners are discouraged against adding raw foods into the diet while still feeding kibble: digestion rates and gastric pH. Our wonderful admin Danielle Steenkamp, DVM helped us point out the flaws in logic of the digestion rate idea in her experiment/case study a couple years ago. In summary: digestion isn’t like a traffic jam, and a healthy digestive system is capable of handling foods that require different rates of digestion – otherwise, our dogs wouldn’t be able to eat raw meaty bones, since meat and bone also digest at different rates.
In this article, I will address the issue of gastric pH, how it relates to healthy function of the digestive system, and whether or not the claims are true…
Are kibble fed dogs’ gastric pH values significantly less acidic than raw fed dogs’, and does this mean dogs are unable to safely consume both raw and dry foods?
What is gastric pH, and why does it matter?
Gastric pH refers to the scale of acidity in the stomach. The pH scale ranges from 0 to 14, with the lowest numbers being the most acidic, the highest numbers being the most basic or alkaline, and 7 being neutral.
Gastric pH is a very important component of digestion. The environment in the stomach has to be welcoming to beneficial bacteria that help the body break down food, but also prevent pathogenic bacteria from surviving and causing infections.
The stomach also has to be an enzyme-friendly environment. There are a handful of different enzymes and hormones that assist in digestion, and many of them are either produced in the stomach, or their production is influenced by the environment of the stomach. The pH is a major factor affecting the production and activity of these hormones and enzymes [source].
A lesson in digestion
We will soon begin our lesson in digestion, but first, a quick lesson in psychology! Ever heard of Pavlov‘s dogs? Pavlov observed that his dogs began to salivate when his lab assistant walked into the room, even if they hadn’t brought food with them, and hypothesized that the dogs associated the lab assistant with being fed. He discovered that he could associate the sound of a bell with food, thus causing his dogs to salivate at just the ring of a bell. That’s what led to his discovery of what we call classical conditioning: a conditioned, but non-learned response to a stimuli.
In this case, the stimuli is the anticipation of food. Turns out, salivating isn’t the only thing that happens when dogs anticipate food. In fact, just thinking about food can begin the first phase of digestion.
Before your dog even swallows a bite of food, the sight, smell, and even just the thought of food triggers the cephalic phase of digestion. Signals from the brain tell cells in the stomach wall to begin to secrete gastric juice. Tasting, chewing, and swallowing further intensify this response. Approximately a third of all gastric acid and pancreatic secretion occurs during this cephalic phase, which can last more than 4 hours in dogs [source].
After food has been swallowed and made its way to the stomach, the presence of food particles stimulates the secretion of a hormone called gastrin. Gastrin’s job is to trigger the production of even more gastric acid, further acidifying the stomach. The extent of gastric acid production required will depend on the content of the meal; hormones regulating gastric acid production respond as needed. If the meal requires higher acidity, more gastric acid will be produced, and vice versa.
During digestion of proteins, a substance called pepsinogen is secreted by the stomach wall. Below pH values of 4 [source], pepsinogen is converted to pepsin, an enzyme that helps break down proteins into smaller polypeptide chains and individual amino acids. Pepsin functions effectively between a pH of approximately 1.5 to 4.5, but is most active around a pH of 2 [source] to 3.5 [source]. Since gastric acid has already been secreted before, during, and after the ingestion of food, the stomach is sufficiently acidic enough for pepsin’s maximal activity.
Lipase, the enzyme that helps digest fats, is most active at a pH of 4 and is irreversibly inactivated at or below a pH of 1.5 [source]. Since the acidic stomach environment isn’t optimal for lipase, the majority of fat digestion in a dog takes place in the small intestine. Amylase in a dog is not present in the saliva like it is in humans, and it also isn’t active in acidic environments, so the bulk of carbohydrate digestion also takes place in the small intestine.
The pH within the stomach also influences what happens outside of the stomach. When chyme (the mix of partially digested food and gastric juices) starts to leave the stomach, the acidic pH stimulates the hormones secretin and cholecystokinin to be produced in the duodenum (the first part of the small intestine). Their jobs are to trigger the release of bicarbonate (which works to neutralize the acidic chyme so it doesn’t damage the small intestine [source]), trigger the release of pancreatic enzymes (proteases to further digest protein, lipases to digest fat, and amylases to digest starch), trigger the liver to produce bile (which further aids in the digestion of fats in the small intestine), and begin to inhibit gastric acid production.
As the remainder of the chyme leaves the stomach, hormones like somatostatin further inhibit gastric acid production by preventing the release of any more hormones like gastrin or secretin.
Digestion continues into the jejunum and ileum of the small intestine.
… But since this article is primarily about gastric pH, not intestinal, our adventure through the digestive system doesn’t need to go any further.
After the meal has been digested, the gastric pH will become less acidic, because it isn’t necessary to sustain a highly acidic environment within the stomach unless gastric juices are needed for digestion; and if the stomach remains too acidic, ulcers could develop. So the pH of the stomach raises slightly, until the next time your dog anticipates taking another bite of food… and then all of this repeats again!
So, as you can see, gastric pH is definitely not constant. It is normal for gastric pH to fluctuate depending on what has been eaten, how much has been eaten, or how long it has been since something has been eaten. Adjusting the pH conditions of the stomach is a normal part of healthy digestion.
What is the difference in gastric pH in raw fed dogs vs kibble fed dogs?
Unfortunately, due to the invasive nature of measuring an animal’s gastric pH, there are a limited number of studies measuring the gastric pH of dogs. The majority of the current studies don’t necessarily focus on optimal canine digestion, but rather use the dog as a model to research pharmacokinetics and how gastric pH can affect the metabolism of certain drugs.
There have been no studies done comparing the gastric pH of raw fed dogs and kibble fed dogs that I am currently aware of (as of January 2018). Most of the recent studies have involved dogs eating a dry food diet, since that is the standard diet for dogs (much to raw feeders’ dismay). However, what limited research we do have available demonstrates that dogs fed dry food still have highly acidic gastric pH: approximately 2 on average [sources: 1, 2, 3].
It is very likely that the average gastric pH does differ slightly between kibble and raw fed dogs. It likely even differs slightly between kibble fed dogs depending on the protein, fat, and carbohydrate content of the kibble, or between dogs on different home cooked diets.
The bottom line is this: at this point in time, there has been no research specifically comparing the gastric pH of raw fed dogs and kibble fed dogs. There has been no research specifically investigating how mixing raw and kibble affects the gastric pH in a dog. Therefore, nobody can truly claim exactly how significant the difference in pH really is between raw vs kibble fed dogs. What we can do is make observations of a dog’s digestive system and consider the evidence.
What does this mean regarding feeding raw and kibble together?
Any time a dog’s diet is changed, there will be an adjustment period. Gastric pH is one factor in that adjustment. This is why a gradual transition is recommended whenever you switch from one diet to another. A gradual transition can be done when switching from kibble to raw too (which is my preferred method for most dogs).
However, the claim that kibble fed dogs actually have neutral or alkaline gastric pH values is completely unsubstantiated and verifiably false. An alkaline or neutral gastric pH would not be able to digest raw OR kibble, and would result in severe malnutrition.
What this means is that the significance of this difference in gastric pH between raw and kibble fed dogs has been highly exaggerated in order to fit some raw feeders’ “all or nothing” agendas.
What we do know based on current research is that dogs fed dry food have highly acidic gastric pH values, and that a dog’s digestive system is well equipped with a complex network of hormones and enzymes that regulate the production of gastric acid. We know that owners have been feeding raw and kibble together successfully for decades to thousands of dogs. And we know that fresh food is very beneficial to the health of our dogs. Considering all of this, if you ask me, it is safe to say we should be encouraging owners to add fresh foods to their dog’s diets in whatever capacity they can.
Sometimes when singing the (well deserved) praises of raw food, raw feeders tend to succumb to bias and misinformation. There is a pervasive air of purism and elitism amongst some (if not many) circles of raw feeders, and it can become easy for them to forget just how many owners simply do not have the means to feed a completely raw diet, despite their best effort. Raw diets can be more expensive, labor intensive, time consuming, and require more resources (like prep and freezer/fridge space, accessibility to co-ops or butchers, etc) than feeding kibble.
But as many raw feeders witness the benefits of raw diets and learn more about the downfalls of dry food, their passion for optimal nutrition can foster a more extremist “all-or-nothing” mindset. I strongly believe this mindset is to the detriment of the dogs whose owners do not have the means to feed raw: instead of being encouraged to improve on their dog’s diets in any capacity they can, they are told that it is actually dangerous to introduce fresh foods into their dog’s diets.
And that is a shame.