Science Says Dogs’ Digestive Systems Evolved with Humans

Eats dirt.
Eats dirt.

I know the “Dogs do not have the enzymes needed to digest grains!!!!!!!!!111!!!11” camp had to be hatin’ this study which found that dogs’ digestive systems evolved over time to better allow them to digest starchy food.  Now there’s more bad news:  another study has found the same thing:

The team then compared corresponding genes in dogs and humans. They found both species underwent similar changes in genes responsible for digestion and metabolism, such as genes that code for cholesterol transport. Those changes could be due to a dramatic change in the proportion of animal versus plant-based foods that occurred in both at around the same time, the researchers said.

Basically, as humans evolved and their diet included more plants, so did dogs who were hanging around humans, eating their “table scraps”. I know this does not fit the “Your dog is a wolf” narrative that has gained such a vocal following among food wonks but there it is.

I don’t intend to advise anyone who is satisfied with their feeding plan to alter it.  If it works for you and your dog, paws up.  I do consider it ignorant bullying when people of the OhNozGrainz persuasion drop in on every food discussion thread they come across and decry the feeding choices of others with no acknowledgement of the emerging science. Please don’t engage in that type of behavior here.  (Not that this will slow anyone down, since they won’t even read it because they are too busy typing ALL GRAINS ALL BAD in the comments, but it seemed like a polite word of warning.)

42 thoughts on “Science Says Dogs’ Digestive Systems Evolved with Humans

  1. :-))
    A (normally) very nice and friendly local raw-feeding list I belong to periodically undergoes attacks by extremists, and I’m getting tired of it. It’s the whole “my dog is healthy BECAUSE of the way I feed it, but your dog is healthy IN SPITE OF the way you feed it” nonsense. I do appreciate that people are passionate about their pets, and experience a “born again” fervor when they discover something new that seems to be the best thing evah. But why the hate? I have been feeding raw for nearly 15 years now, but I have no problem helping someone pick the best kibble, if that is what they need to do. There is more than one “right” way to care for a dog.

    1. I appreciate that attitude. There is no faster way to drive people away from your feeding philosophy than to hit them with “You’re killing your dog” right out the starting gate.

      On Sun, May 19, 2013 at 11:46 AM, YesBiscuit!

    2. Agreed. And all dogs are, like all people, individuals. What works for one may not work for another. You have to find what works for your dog as an individual.

    3. Wish I could find a raw feeding group like yours. The most of the ones I’ve found are on the extremist end of the scale, and although they CAN be very helpfull to someone who wants to feed Prey Model, god forbid you mention something that doesn’t exactly fit those parameters. Heck, I got nasty messages (ON the yahoo group, and yes its fully moderated), as well as by private email, for 3 weeks after I mentioned that I thaw my bulk purchases in my tub under dribbling cold water….needless to say I don’t recommend the group to any new raw feeders I come across, and have specifically warned some folks away from it.

      Personally I don’t HATE all grains. I have a HUGE issue with corn in pet food but that has to do with the fact that so many companies would rather use corn as a protein source than animal products, which I don’t think is right. I personally prefer grain free if I’m going to recommend kibble, but some grains, as long as they aren’t meant to be the protein source, don’t bother me.

      Personally as long as your dog is happy and healthy on the food you’re feeding him I don’t really care what it is. But if you tell me he’s got horrid gas, and he always seems to be itchy but the vet can’t find anything, I’m going to suggest a food change and will do so with my bias in mind!

  2. my dogs would walk across hot coals for a pizza crust They eat almost everything like good scavengers should!!!! I do get a kick out of my show dog buddies who haul water from home in huge jugs ..because “hotel water” ie Motel 6 water LOL is bad for dogs.. only to see their dogs run out and drink from a mud puddle

  3. As a raw feeder I’ll do my best to hold back and not scream about “No grains” but I do feel it’s necessary to point out that not all are “Vegetables” grains. Yes, I have read the studies and yes, they do show that dogs are better at digesting “vegetable material” than wolves. This means that dogs can survive on an omnivorous diet better than wolves but, that does not translate into “dogs can digest grains”. The simple fact remains that dogs do not produce digestive amylase in sufficient amounts to effectively handle the huge amounts of grain in modern dog food. Anyone who has researched this subject even a little bit will come across numerous articles in the scientific literature regarding studies done on LIVING dogs that show this to be the case. Further study will also turn up a slew of recent papers that show that even we humans do better on a low grain/starch diet. The culprit seems to be gluten, a protein found in wheat, barley, oats, rye and corn among other grains. Some studies indicate that as much as 50% of all humans have at least a mild allergic reaction to this very difficult to digest molecule, 5-10% have mild gluten sensitivity and up to 1% actually suffer from active celiac disease (since the 50’s the amount of gluten in wheat has risen by 500%!). In my experience this seems to mirror the case in dogs as well. You only have to look as far to your yard to see this. You see the “proof” is in the poop. A dog fed dog food will defecate often and voluminously and the odor of its droppings is well…foul. In contrast, a raw fed dog will only defecate once or twice a day and the resulting feces are virtually odorless and dry to a white powdery consistency. Why is this? Simply because the grain in dog food passes through the dog UNDIGESTED. Because it is not digested properly it begins to ferment in the dog’s gut. This is what gives the dog’s leavings that wonderful fragrance we have all to come to know and “love”. Anecdotal evidence (and my own experience) would also indicate that raw fed puppies are more resistant to disease (including Parvo) and recover more quickly than those fed dog “food”. All of the above goes double for cats which have little to no ability to digest vegetable material. Sorry if I’ve run on on this subject but it is one that I have studied at length. This desire to learn more is the direct result of my own experience feeding dog and cat “food” to my animals and the resulting pain (for me and my animals) and expense I inured as a result. But, don’t believe me, do the research yourself. Better yet, give it a try and see the results. You WILL be amazed.

    1. My dogs are vegan. They poop 1-2 times a day. It does not small any worse than their poop did on a raw diet. They don’t poop more than on a raw diet. They are no less healthy than on a raw diet. My older dog is far healthier on a vegan diet. I’ve had puppies on various diets and none were more or less prone to parvo.

      So enjoy your anecdata, I’ll enjoy mine (um, except it’s backed by science whoa), and we can just go about feeding our dogs whatever we’re comfortable with…so long as they are healthy and happy, no one needs to go on internet diatribes, yo.

      1. REALLY? Your dogs are healthy? By what standard? Can you direct me to the “science” behind your statements? You see, I have yet to find even a single paper or study that has shown this. Yes, HSUS and PeTA both claim that a vegan diet is “safe” to feed dogs AND cats, both claim that there is “science” to back up their claims and both have refused to date to provide any proof but, to date NO ONE has actually seen ANY research to show that this is true. There are however studies and papers that ACTUALLY show that dogs fed on a raw diet have greater muscle mass and are much better at utilizing the protein in their diets. So, in actuality, this information is anything but anecdotal. Here’s an anecdote for you: 3 years ago my girlfriend and I were given what appeared to be a healthy 8 week old American Bully puppy. He was one of 10 pups in the litter and within a week all 10 broke with Parvo. Our dog which was raw fed by us from day one was taken to the vet as soon as he became symptomatic and imagine our surprise when we found his brothers and sisters at the same vet’s hospital! To make a long story short he recovered in less than 2 days with only hydration support while his brothers and sisters died off one by one in spite of the Dr’s best efforts. The vet (over 20 years in the biz) told us he’d never seen a puppy recover so well or so fast from Parvo. “What are you feeding this guy?” was his only question to us.

      2. I love talking about food. I don’t post on the topic more often because of the badgering and bullying it invariably brings out. Please knock it off.

      3. Hey Willy,

        There is a veritable treasure trove of peer-reviewed journal articles on the efficacy of grain-based diets. You can do the research yourself – I am not your google!

        And yes REALLY ZOMG! SHOCKING, my dogs are healthy. My 6-yr-old dog is very healthy. My 14.5 yr-old dog is old, crotchety, and has mast cell tumors, UTIs, and hypothyroidism. She had those issues on a grain-free, single-dead-animal sourced dog food and she had the last two while on a raw meat diet!

        The standards I use are based on a) my dogs’ overall health; b) my dogs’ physical health and energy level; c) my veterinarian’s analysis of their blood-work and physical structure; and d) my dogs opinion on life. You are welcome to feed your dog(s) whatever you deem is appropriate for them. And I’ll do the same.

    2. “A dog fed dog food will defecate often and voluminously and the odor of its droppings is well…foul. In contrast, a raw fed dog will only defecate once or twice a day and the resulting feces are virtually odorless and dry to a white powdery consistency. Why is this? Simply because the grain in dog food passes through the dog UNDIGESTED. ”

      No. It’s because the white stuff is what’s left from digesting bone. Spotted hyenas eat large amounts of bone, and their poop is white. All it means is your dog is eating large amounts of bone.

      Grains (and veggies) have fiber. Some fiber is not digested. Thus, larger poop. More undigestible fiber, more poop. Not rocket science. Not much to do with grain being digested, or not, either. If it wasn’t being digested, you’d see it, recognizable, in the feces. Feed your dog a whole raw carrot sometime and see what comes out.

      If grain was ‘undigested’, meaning no energy or other nutrients were extracted, dogs would be starving to death left and right. That’s not the case, though, is it?

      Since you have ‘studied at length,’ I would like to see citations for each of your ‘study’ claims. Just make a list, no need to provide abstracts or links, thanks in advance. I’m always interested in such things, you see.

      1. Thank you for proving my point. Yes, the white stuff is DIGESTED bone. The excess calcium carbonate and calcium phosphate pass through the dog (or cat) but, as the bone is completely broken down it has in fact been digested. If you have the inclination, check closely and you’ll find that the feces of kibble fed dogs is composed largely of UN digested grains and vegetable products. Yes, it’s ground up and yes, it’s been partially broken down by the stomach’s acid but no, it has not been broken down at the microscopic level or absorbed by the dog’s body. Dogs fed vegetable material produce less effective (lower molarity) stomach acid and have less effective immune systems. This allows bacteria to pass into the gut and proliferate. I’ll give you a list in a few days (traveling today) In return perhaps you can provide me with a list of papers that show how good kibble and vegan diets are for dogs? Don’t even get me started on cats!

      2. EEEENT! Excess calcium is not excreted in the feces of dogs (bones are not made up solely of calcium, by the way.)

        EEEENT! The fact that you can’t distinguish between undigested food and indigestible fiber means you are in all likelihood parrotting junk you picked up somewhere else.

        Don’t bother with making up a list, if you’re going to get the calcium excretion thing wrong, who knows how you’re going to (deliberately) misinterpret some unoffending studies. I consider Pubmed recreational reading, you will not find any studies stating that dogs that eat plant material have ‘less effective immune systems’ there because there are *no such studies.* Don’t lie. It doesn’t do your ’cause’ any good.

        And before you start making accusations regarding what I ‘believe’ about dog diets, you might want to check my blog and educate yourself a little bit about me. Hint: there’s no dogma allowed there. I’ve owned (and fed a home made diet to) enough dogs to conduct my own AAFCO feeding trial for more than a decade. Excuse me if I’m not impressed by your paraphrasing the unproven claims of people who have an agenda that has far more to do with religious fanaticism and “I’m a better owner than you are” than with actually feeding dogs according to their needs.


    3. It’s evident that grain doesn’t pass through a dog’s gut totally undigested- otherwise a dog fed only on grain would die quickly. Bacteria will do some work on it like it’s supposed to, just like it does if you feed a dog meat. Hence why antibiotics can give you digestive problems. I’d be worried if bacteria didn’t act on digested food inside the dog’s gut.

      And why would the fact that bacteria eat the digested material make for larger feces?

      How is larger shit indicative of the health or otherwise of a diet for a dog? Or, for that matter, why would a smell humans don’t like be a sign of ill-health? Presumably if a dog gets more fibre, the stool will be softer and larger, and there will be more of them. I’m not sure where the connection to health comes in. It’s easier to pick up, sure. But none of this is evidence that raw feeding could be better for dogs, much less ‘proof’ that it is.

      Dogs seem to tend to to develop allergies to meat proteins (for example proteins found in beef). It doesn’t mean meat is bad any more than peanuts are inherently bad, or gluten is bad- they could be bad for other reasons, but not simply because animals can be allergic to them. The number of allergies to something are caused by both allergenicity and the amount of people who are exposed to it. So you’d expect to see more allergies to gluten than to, say, proteins found only in armadillo meat.

      Not trying to be combative, I’m just having difficulty following your argument. There seem to be some leaps of logic.

      My anecdotal evidence would suggest that ordinary dog food and supermarket cat kibble leads to an above-average lifespan for the cats and dogs fed on it. Provided, of course, the animals are kept away from hazards, and aren’t from short-lived breeds. Of course anecdotes are worth almost nothing in establishing the truth or otherwise of health claims. That’s the problem- most dogs will live a reasonable lifespan if they’re from the right breed and lucky, and kept pretty well. So most pet owners could have an anecdote or two about their pet diet/regime and how amazing it is.

      “Give it a try and see the results”- I’d rather see some more evidence before I experiment on my animals. Like good, well-controlled, large studies of health and longevity (typical raw food vs typical commercial food) with some effort at blinding, rather than anecdotes and preliminary research.

    4. Why are you referring to “dog food” as though there’s only one type? Are you aware that there are many varieties of commercial dog foods available, and that while many dry foods contain primarily corn, some have other grains in varying proportions, and some have no grains at all? I’ve noticed a lot of elitist rawists like to set up this false dichotomy, that “dog food” is high in grains and therefore terrible and therefore you MUST feed raw.

  4. Boom!

    Mina is all about the grains and veggies and fruits and everything that isn’t a dead animal. Celeste wishes she could eat every fuzzy creature on earth but she loves her celery, carrots, rice, wheat, and, well, any food I’m eating!

  5. I think the photo caption nicely sums up dogs’ nutritional proclivities. Does it fit in my mouth, or will it if I gnaw long enough? Food! Ensuring that your dog’s mealtimes do not involve any ingredients otherwise packaged with a skull and crossbones (or for puppies, a Mr. Yuck) label is mandatory. Beyond that, you risk slipping into into the precious zone. Grain consumption is not the leading cause of canine deaths and even the Xtreme Edition of wheat (“Now, with more gluten than ever!”) has not, to my knowledge, decimated any dog cohort or shortened its average lifespan.

  6. In the anecdotal evidence department, I have made it a point over the years to inquire after the diets of any particularly long lived dogs I’ve come across. With the exception of one dog whose owner provided me with a recipe she prepared for the dog (it was a combination of raw meat and “cakes” made from various other foods as I recall), they were all primarily fed kibble.

    I don’t read too much into that other than the fact that most dogs in this country are fed kibble. It doesn’t indicate to me that feeding kibble leads to a long life span. By the same token, it doesn’t exactly lead me to believe that feeding kibble leads to early death.

    1. A lot of the hardliners I’ve come across seem to be genetic denialists of some sort; nurture over nature, if you will. The absolute worst, IMO, are breeders who have ‘health warrantees’ that are void unless you feed the breeders special brand of fanatic diet.

  7. My dogs eat what I eat, for the most part, minus the onions and grapes, fermented and otherwise. They beg for banana, oranges, strawberries, kale, beans, lentils, barley, brown rice…you get the idea. Both very lean and healthy.

  8. I’m surprised to see such vitriol directed against a group of folks who love their pets just like you love yours. People who have arduously and rarely willingly crossed far outside their comfort zones and dug deep past the last 100 years of pet food “teachings” to seek what we ALL want – the healthiest lives for their beloved pets. Almost all who come to raw feeding do so not because they want to, but as a last-ditch, desperate effort to heal their pets of a sickness brought on by commercial pet food ingredients. Their passion has its roots in the “miracle” of healing that feeding a fresh, meat-based diet wrought in the lives of their furbabies.

    Since it’s abundantly clear you despise pet owners who understand and feed fresh, species-appropriate diets, I won’t waste any of your time discussing the topic. But the studies you reference aren’t “bad news” to anyone who understands species-appropriate nutrition, as they do nothing more than indicate that dogs are adaptive carnivores; dogs are still *carnivores* and the differences between dogs and wolves are so genetically insignificant the two can and do breed.

    Just because it’s been asked (and I am apparently a masochist), here are two more studies, one by a pet food company, showing the benefits of feeding carnivores a fresh, meat-based diet.

    Relationship Between the Domestic Dogs’ Well-Being and Life Expectancy Statistical Analysis, Gérard Lippert, and Bruno Sapy, Brussels, Belgium, August 2003 (

    ORIJEN_White_Paper, The Biologically Appropriate Food Concept and the Dietary Needs of Dogs and Cats, University of Pennsylvania Philadelphia, Pennsylvania, Purina Nutrition Forum, 1998 (

    1. “Since it’s abundantly clear you despise pet owners who understand and feed fresh, species-appropriate diets”

      LOLOLOL. Yes, that’s me. You’ve got me pegged, totally.

      1. Hm. I’ve been feeding prey model raw for 12+ years. And yet, I didn’t feel the sting of vitriol when I read this blog post. Maybe I’m doing it wrong, but I saw good news in it for those who choose to NOT feed prey model raw.

        Grains were detrimental to my dogs’ health – yeasty ears, yeasty skin, aggravating arthritic symptoms. So I don’t feed grains. My choice. What others do is theirs.

      2. You will feel the full force of my wrath when we go out for pizza and I snatch the crust from you, scraping only the cheese and sauce onto your plate while yelling “No grains for you!”

        On Mon, May 20, 2013 at 10:48 AM, YesBiscuit!

  9. My reason for using an all-grain food is entirely pragmatic. I have 4 large dogs of my own. At the moment, I also have 5 foster dogs (though I like to keep that to 1 or 2). I have a 25 x 50 fenced area off the attached garage on my 5 acres in the country.

    Do you know how much poop I must pick up every day (twice a day)? The no-grain food makes them more solid (easier to pick up) and I feed less (with less “waste” out the other end). If I feed a grain-based food, then I have to feed twice as much and pick up twice as much because dogs only digest a very small amount of the grain. The tremendous (over-) amount of grain in processed dog foods has more to do with the industrial extruding process than it does with whether dogs NEED that much grain.

    To my mind, humans’ need for whole grains is related to our amazingly long digestive tracts (unlike dogs), our longer lives (unlike dogs), and our dependency upon McDonalds-type “cuisine” (unlike dogs.” Just as I don’t anthropomorphize about my dog’s behavioral needs, I also don’t anthropomorphize about my dog’s health needs. Dogs are dogs. People are people. And just because our digestive systems have undergone similar evolutionary changes, we are not the same species.

    But, interesting research all the same. Just don’t take it to the opposite extreme. I’m sure none of the research authors is claiming that we should have identical diets.

    1. I think you mean a no-grain food, not an “all-grain food” right? My reason is entirely pragmatic, too. I don’t like having corpse fragments in my kitchen. I do use Prozyme enzyme supplement to assist my dogs’ evolving digestive system. But I hear ya about the poop and the foster dogs. I’ve had as many as seven foster pups plus eight foster kittens at any given time. It’s a lot of work! Thanks for helping them!

  10. “food wonks”, lol! You are right about the bullying too. It’s that same mindset of the murderous crusaders of olden dayd…

  11. I don’t believe grains are bad. I do know aflotoxins are bad. And I know that the commercial pet food mfg. frequently have aflotoxins in exceedingly high and toxic levels of the grain they use.
    Also GMO crops are used in commercial pet food. I don’t think any species have evolved yet to handle that.

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