This is incorrect, and here’s why.
For domestic dogs, grains and vegetables are perfectly fine and are desirable in a healthy diet as they provide important sources of energy and essential vitamins and minerals.
Dogs are omnivores, separated from wolves and other carnivorous canids by 12,000+ years of domestication and selective breeding by humans. They have evolved alongside agricultural humans, surviving on our grain-based foods and our scraps/trash by scavenging, and have become designed to eat diets that are nowhere near the same as their wild cousins. There is significant evidence of this in the way our domestic companions exhibit dental changes and genetic changes divergent from their wolf cousins, as well as the proneness toward severe dental disease in many breeds and the onset of acute pancreatitis in most dogs when they cannot handle the fat content of meats.
There is a fantastic study, A key genetic innovation in dogs: diet, which was done on the genetic changes and evolutionary diversion that domestic canines have undergone and how that affects their diet and digestion — specifically their genetic coding for the production of pancreatic amylase (AMY2B), which breaks down starch into the sugar maltose in the small intestine.
Related canids like the wolf, coyote, and golden jackal have two copies of the AMY2B gene. Most domestic dogs, however, have more than this, and in some cases many-fold more. These duplicate copies of a gene are called “copy number variations”, and they often occur during DNA replication. In the case of the amylase gene, dogs with more copies of the gene produce more of the enzyme amylase — which allows them to digest starch more efficiently.
The domestic dogs with only two or very few copies of the gene include the most primitive breeds and some of the spitzes (Dingo, Greenland Dog, Siberian Husky, Pug, Laika, etc). These breeds are closer to their shared wolf ancestor and less selectively bred and changed.
Among breeds that typically average more than 12 copies of the gene are the English Springer Spaniel, German Shepherd, Rottweiler, Border Collie, and Whippet. The breed with the most AMY2B copies determined so far is the Tazi, with an average of about 18 and some individuals with more than 20:
In another study, Differences in the gut microbiomes of dogs and wolves: roles of antibiotics and starch, researchers surveyed the gut bacteria of 27 domestic dogs, which were fed commercial dog food, and 31 wolves, which were fed uncooked meat. They completed this by using 16S rRNA sequencing. In addition, they collected fecal samples from 5 dogs and 5 wolves for shotgun metagenomic sequencing to explore changes in the functions of their gut microbiome.
The results showed a higher abundance of putative α-amylase genes (P < 0.05; P < 0.01) observed in the dog samples vs. wolf samples:
In yet another study, Changes in feeding habits promoted the differentiation of the composition and function of gut microbiotas between domestic dogs (Canis lupus familiaris) and gray wolves (Canis lupus), multiple fecal samples were collected over the course of 2 months from four adult wolves and three adult dogs living in the Dalai Lake National Nature Reserve in the Inner Mongolia region of northern China.
Analysis of the gut bacteria of these animals revealed that the biggest differences observed between wolves and domestic dogs were in microbial species and genes involved in starch and cellulose metabolism. The study confirmed what many others have also established — that domestic dogs carry a significant enrichment of genes involved in carbohydrate metabolism as well as amino acid metabolism. These genes support a complex diet intake and an enhanced ability for polysaccharide absorption in domestic dogs.
The study specifically describes how the most abundant families (groups) of gut flora in domestic dogs are Ruminococcaceae and Desulfuromonadaceae, both of which are related to cellulose digestion, and Lactobacillaceae, members of which are related to the fermentation of glucose:
“In particular, the significantly higher abundance of genes involved in valine, leucine and isoleucine biosynthesis (ko00290) and nitrogen metabolism (ko00910) in domestic dogs also revealed that the gut microbiota of domestic dogs is more active in branched-chain amino acid (BCAA) metabolism. Some previous studies of gut microbiota also showed that the significant differences in these two pathways corresponded to a low animal protein intake (Rampelli et al. 2015; Schnorr et al. 2014).
This result is in line with the low contribution of meat to the diets of domestic dogs.”
The study also established that the gut flora of domestic dogs can synthesize cysteine more efficiently than wolves, by producing cysteine directly from starch-rich foods. Cysteine plays an important role in animals, and the lack of this amino acid can lead to several diseases.
They postulated that wolves consume sufficient amounts of cysteine from meat due to their wild carnivorous diet. The diet of domestic dogs, however, has more starch and cellulose than cysteine. To avoid illness caused by a lack of cysteine, their gut flora needs to supply a large amount of cysteine to their hosts. Domestic dogs have evolved a more efficient way of synthesizing cysteine for themselves.
“According to the results of this study, we determined that most of the bacterial taxa at the family and genus level that have a more significant presence in dogs than in wolves are related to cellulose and starch digestion, and the most significantly different enzymes were associated with carbohydrates, especially amylose, sucrose, and maltose. Therefore, we believe that the significant differences in these bacteria and enzymes have a direct relationship with the changes in the diets of dogs resulting from the domestication of dogs by humans.”
How would dogs benefit from extra copies of a gene for starch digestion, or gut bacteria designed to process carbohydrates?
Dogs followed humans around the globe and lived where they did, and what was available to eat locally would be reflected in the diet of both. One of the key innovations that allowed expansion of humans across Asia and into Europe was agriculture – the ability to keep livestock and to grow crops for food.
Dogs were used to guard and manage livestock, but the animals were how shepherds made their living and were extremely valuable. They were not the food source for the shepherd and his dogs. Instead, they were used as a renewable resource, providing milk on a regular basis and reproducing yearly to produce the income of the next season. Eating the livestock would be self-defeating, like spending the principal in a savings account instead of just living on the funds produced by earned interest. Instead, the dogs and their shepherds lived primarily on their renewable resources, grain and milk, perhaps with an occasional wild animal for meat, so both had diets that were high in starch. Dogs with more copies of the AMY2B gene would be more efficient at digesting starch, and if this was a major component of the diet it would drive selection for an increase in the number of copies of the gene.
What is the evidence to support this scenario?
A survey of dogs from around the world found that dogs from “agrarian” areas (red) had more copies of the AMY2B gene than dogs from “non-agrarian” areas where plant crops were difficult or seasonally impossible to grow and comprised less of the diet of both humans and dogs (blue).
You can see from the map below, on which the dash lines mark the approximate extension of prehistoric agriculture, that from the ancestral number of copies of the gene (two) in wolves and other related carnivores, the number of copies increased as much as 11 fold (to 22 in both the Tazi and the New Guinea Singing dog) in dogs from agrarian regions. This held not just for the “breed” dogs, but also for the native village dogs in those areas. The dogs with the fewest copies of the AMY2B gene were from areas where the climate was not suitable for large-scale agriculture, and fish and meat likely formed a greater proportion of the diet (e.g., Greenland dog, Siberian Husky):
Arendt M, KM Cairns, JWO Ballard, P Savolainen, & E Axelsson. Diet adaptation in dog reflects spread of prehistoric agriculture. Heredity 2016: 1-6.
Marciniak S & GH Perry. 2017. Harnessing ancient genomes to study the history of human adaptation. Nature Reviews Genetics 18: 659-674. doi:10.1038/nrg.2017.65
Pennisi E. 2016. How farming changed the dog. Science 360(6391): doi:10.1126/science.aal0353
But wait, there’s more!
Another recent study that further explores the genetic changes behind increased production of amylase states:
Over time, and via cohabitation, the canine diet has been transformed from the carnivorous diet of its ancestor, the wolf, to a diet more closely matching that of omnivorous humans…This transformation increased variation in the domesticated dog’s diet, potentiating impact on numerous biological pathways.Reiter T, Jagoda E, Capellini TD (2016) Dietary Variation and Evolution of Gene Copy Number among Dog Breeds. PLoS ONE 11(2): e0148899. doi:10.1371/journal.pone.0148899
Yet another study was conducted by evolutionary geneticist Erik Axelsson from Uppsala University in Sweden. He and his colleagues sequenced DNA from 12 wolves around the world and from 60 dogs belonging to 14 breeds. They found 10 key genes specifically giving dogs the ability to digest diets rich in starches:
Ten genes with key roles in starch digestion and fat metabolism also show signals of selection. We identify candidate mutations in key genes and provide functional support for an increased starch digestion in dogs relative to wolves. Our results indicate that novel adaptations allowing the early ancestors of modern dogs to thrive on a diet rich in starch, relative to the carnivorous diet of wolves, constituted a crucial step in the early domestication of dogs.Axelsson, E., Ratnakumar, A., Arendt, M. et al. The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature 495, 360–364 (2013). doi:10.1038/nature11837
More specifically, their sequencing determined that dogs had 30 copies of the gene they discovered that is responsible for the production of amylase. Wolves have only two copies, one on each chromosome.
As a result, that gene is 28-fold more active in dogs than in their wild relatives. More copies means more protein, and test-tube studies indicate that dogs should be FIVE times better than wolves at digesting starch (corn, wheat, rice, etc).
Dogs and wolves also showed that they have the same number of copies of another gene labeled MGAM, which codes for the production of maltase — another enzyme important in starch digestion.
But there are four key differences between the sequence in dogs and in wolves. One difference causes dogs to produce longer chains of maltase. That longer protein is also seen in herbivores, such as cows and rabbits, and omnivores, such as lemurs and rats…but not in other mammals, suggesting length is important specifically to plant-eaters.
That last point brings us back to a paragraph I mentioned earlier, when discussing a study that showed domestic dogs have significantly high populations of Ruminococcaceae in their gut flora. Members of that genus of bacteria are specifically important in breaking down the cell walls of plant material during digestion. Humans have a type of Ruminococcaceae in their GI tracts, as do pigs (both of which are omnivores) — but it is primarily found in many herbivores such as cows, horses, and rabbits. In fact, the name is derived from the fact that it was first isolated from the rumen (2nd stomach) of a cow.
According to this paper, ruminococci are predominantly associated with herbivores and omnivores, and very few examples of this bacteria are found consistently in “non-host-associated environments”. Which means it could possibly be found in one dog, but would not be repeatedly and consistently found in all dogs as it has been, unless those dogs are established hosts — which we know are herbivores and omnivores.
Thus the genes that create longer chains of MGAM as well as the consistent presence of Ruminococcaceae would both support domestic dogs being omnivorous, having evolved to thrive on a diet rich in plants and grains.
It is all related and interconnected!
But what about wolves?!
Even with that all that said, wolves do consume significant amounts of plant material and digest it very effectively.
In fact, a study on Yellowstone wolves that analyzed their feces (scat) determined that during summer months, the wolves kill 25% less prey and make up that portion of their diet with available small mammals, fruits, berries, plants, and primarily grasses:
As most of our information on wolf kills comes from winter data, kill rates and prey selection are less known in summer. Current studies exploring this aspect of wolf predation are under way, but preliminary evidence indicates that wolf kill rates decrease as much as 25% in the summer (D. Smith and D. Stahler, Yellowstone Wolf Project, unpublished data).
One indication of the seasonal differences in wolf foraging patterns is through an analysis of summer wolf scats. Scat analysis shows that summer diets are more diverse and include smaller prey species such as rodents, birds, and invertebrates, as well as ungulates, otherwise absent in the winter. Analyses of summer scats in 2003 show that mule deer was present in 133 (25%) of 530 scats analyzed.
In addition, plant matter is prevalent in wolves’ summer diet, with 392 (74%) of 530 scats analyzed containing some type of plant material, largely grass (Graminae). This is consistent with summer observations of wolves consuming grass and other plant material.Daniel R. Stahler, Douglas W. Smith, Debra S. Guernsey, Foraging and Feeding Ecology of the Gray Wolf (Canis lupus): Lessons from Yellowstone National Park, Wyoming, USA, The Journal of Nutrition, Volume 136, Issue 7, 1 July 2006, Pages 1923S–1926S, doi:10.1093/jn/136.7.1923S
This data observation is interesting, as it suggests that wolves only hunt prey at the rates observed during winter because other food sources are not available. During the summer months, they prefer to utilize more plant material in their diet and intentionally choose those plant sources over hunting prey items.
They are choosing to eat vegetation over meat.
IN THE END…
I always tell clients that despite what the trendy pet food bags depict, these animals are not wolves nor even close to wolves, as we have bred them to be so far diverged from their ancestors that any historical link is almost unrecognizable and their genes show this:
WHAT ABOUT FELINES?
Cats on the other hand are obligate carnivores, much less removed from their wild ancestors in design and function as they bred naturally (for the most part) and have had no overly drastic changes to their physiology. They also cannot synthesize Taurine like dogs can — which is an essential amino acid that is critical for heart function among many things. This means they need a primarily meat-based diet with Taurine added.
That said, cats CAN digest some grains and vegetation, and do obtain useable energy from it, so inclusion is not harmful as long as it is not making up the bulk of the diet.
These inclusions are also beneficial, as too much protein in a cat’s diet greatly increases the intake of phosphorus, which directly contributes to kidney disease, kidney failure, and urinary tract issues (crystals, stones, infection, etc).
In the end…
The “grain free” trend among today’s pet foods is simply a marketing ploy utilized by manufacturers to sell their product, and has no scientific basis whatsoever. This has been debunked many times by both the veterinary community and scientific community.
Tufts University recently did a study comparison of grain-free vs. grain-inclusive diets, and published the results in the Journal of Feline Medicine and Surgery.
They also followed up with an article addressing the analysis as well. Here is a segment from the article:
All dry cat diets contain carbohydrates of some kind. The grain-free cat diets we investigated swapped grains for peas, potatoes, sweet potatoes, and tapioca (think of the pudding!). These ingredients are no more “natural” or healthy for your cat than grains.
There is also a current issue regarding Boutique diets (including homemade raw), Exotic protein sources, and Grain-free diets — together called “BEG” diets. These diets are currently being linked to thousands of cases of dilated cardiomyopathy (DCM) in MANY dog breeds, with golden retrievers being one of the most common by far. This issue is now also being seen in cats as well by practitioners at cat-only hospitals. Many young dogs are suddenly dying with no forewarning or illness. Others are becoming ill out of nowhere, only to be diagnosed with congestive heart failure caused by DCM.
Researchers are theorizing that a common ingredient in these diets is somehow causing an interruption in the absorption and utilization of Taurine at the cellular level. Over 90% of the affected animals show normal Taurine levels in their blood, which means they are taking in enough of the amino acid, but something may be preventing it from being utilized in the body.
In the past, legumes have been implicated in this issue — specifically Beet Pulp. Unfortunately, almost all grain-free diets include legumes, lentils, and/or pulses.
The top brands implicated by the FDA and in the studies at UC Davis are Acana, Zignature, Taste of the Wild, Fromm, 4Health, and Blue Buffalo. Over 30 BEG diets are currently of concern:
Further, the breakdown of most common suspect ingredients is as follows:
Studies are ongoing, but for now, universities and veterinarians are advising pet owners to avoid these diets, and if they’ve been fed a BEG diet, to have their pets examined in order to catch it early. Switching to a grain-inclusive food that meets WSAVA guidelines as mentioned previously in this article is showing promise in reversing DCM in affected dogs.
Important links regarding this issue:
SO WHAT SHOULD I FEED MY PET?
Unfortunately there is no “Best Food” or one-size-fits-all approach. This is definitely a discussion a pet owner needs to have with their Veterinarian, as that doctor knows the health and history of that specific pet. Some pets have kidney issues, heart issues, skin issues, etc. that will require specific dietary plans.
In general, for healthy animals with no organ function issues or sensitivities, I always tell clients to look for:
- Age-appropriate biologically-oriented moderate protein foods.
- Foods which meet/exceed WSAVA (World Small Animal Veterinary Association) standards.
- And which meet/exceed AAFCO regulations.
- Foods/brands which have undergone numerous food trials/studies.
- And which are made by companies that employ full time ACVN board-certified veterinary nutritionists.
Here is WSAVA’s guidelines questionnaire for pet owners: