At least that’s the propaganda that you are likely to hear since the publication of a fascinating study in the scientific journal Nature in January of 2013. The exact summary statement from the report actually says:
“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.”
The underlying premise of the study is that for the wolf to transform into the dog, it had to adapt to the relatively high carbohydrate table scraps that humans had to offer. This adaptation necessitated genetic changes allowing for better starch digestion.
It’s tempting for those of us who favor low carb, raw, ancestral diets for dogs, to reject this research out of hand because it doesn’t conform to our beliefs. I propose that instead of sticking our heads in the sand, we need to face the findings and see what we can learn from them.
The study was conducted by a group of evolutionary geneticists from Uppsala University in Sweden. I have no doubt that these scientists know their specialty. It took me several hours to read every line of this study. I found the report to be very dense in content and rich in technical, genetic jargon, which made the details nearly inaccessible to anyone who doesn’t hold at least a PhD in genetics.
So in my subsequent online discussions of the research with my veterinary colleagues, I found that very few bothered to read more than the summary paragraph. I think the main reason for their complacency is that the conclusion of the study reinforced the conventional view of nutrition, so no critical evaluation was deemed necessary. Besides that, it was simply too difficult to read and comprehend. In this article, I’ll attempt to translate what I’ve learned from this study, interpreting the results as I go.
What Researchers Found
The researchers compared the DNA of 12 wolves from around the world with that of 60 dogs of 14 diverse breeds. They found genes that were different between the two groups and that had characteristics that indicated adaptation to new circumstances. Some of the mutations were in genes involved with brain development, which the researchers interpreted as relating to the less aggressive temperaments of dogs compared to wolves.
But the focus of the study was on other genetic changes that involved the digestive system. The researchers first established that the digestion of starch requires three steps.
The first step in the breakdown of starch requires the digestive enzyme amylase.
The second step necessitates an enzyme called maltase-glucoamylase.
The third step in starch processing requires a protein called SGLT1 to transport glucose from the gut into the bloodstream. The scientists proceeded to show to their satisfaction that dogs evolved away from wolves in all three of these steps.
Regarding Step 1, the researchers first found that dogs had between four and 30 copies of a gene that codes for amylase while wolves had only two copies. This indicated to them that dogs have a higher capacity to perform the first step in starch digestion. I agree it’s significant that dogs have between four and 30 copies of the amylase gene, and this wide range would indicate that some dogs are much less able to handle starch than others.
Next, they compared the expression of that gene in dogs versus wolves and found on average a 28 fold increase in dogs. They also tested the blood for enzyme activity and found a more than fourfold increase in dogs as opposed to wolves.
But one expert I talked to stated that increased gene expression doesn’t necessarily mean increased enzyme production. I would also add that the expression of such a gene as well as the enzyme activity would depend on the diet being fed. A high starch diet (most standard dog food) would turn on the needed genes as opposed to a low carb, wolf like diet. So the first part of the above work indicates that dogs have more genes for the first enzyme needed for starch digestion, but the second part proves nothing.
The researchers now moved on to Step 2. They didn’t find a higher number of genes coding for maltase-glucoamylase in dogs as compared to wolves. However, they were able to determine that there were significant differences in the gene responsible for that enzyme between dogs and wolves. They compared the canine mutations and found that when those same mutations occurred in other mammals, it often indicated a tendency toward the animal being omnivorous. They hypothesized that the gene mutations mean that in dogs, the enzyme is more effective at its job of digesting starch.
To test their hypothesis, the researchers measured the amount of maltase-glucoamylase in the pancreas and in the blood of dogs compared to wolves. They found higher levels in dogs. They admit that the difference in enzyme levels could be due to diet, and once again, the more carbs in the diet, the higher the enzyme levels are likely to be. Since wolves eat a low carb diet compared to most dogs, the researchers really did not prove anything conclusively about Step 2 of starch digestion, as far as I can see.
For the third step in starch digestion, the researchers focused on the gene coding for SGLT1 (the protein that transports glucose into the blood). They found that this gene too had mutations in the dog as opposed to the wolf. They then surmised that this change meant that the dog protein must be better at glucose transport. They showed that the dog version of SGLT1 is different than that of the wolf but did not prove that this difference is meaningful. Of course, if you believe that dogs evolved to handle starch better than wolves do, then it follows that this genetic difference proves your point.
This genetics study published in Nature attempted to prove that domestic canine DNA is different than that of wolves and that some of this difference indicates that dogs can digest and utilize starch better than wolves. They do show genetic differences but fail to conclusively prove that these differences mean that dogs “thrive” on a high starch diet.
Have Dogs Evolved To Eat Grains?
It really shouldn’t surprise anyone that dogs and wolves are not genetically identical. I have to admit that this research does suggest that dogs may be better able than their wild counterparts to handle starch in their diets. It is very likely that evolution is at work in domestic dogs when it comes to diet. But to really understand the ramifications of this statement, we need to review how evolution works.
No individual evolves from a genetic point of view. Instead, populations of animals evolve due to changes in living conditions they must adapt to. Rare individuals are born with a mutation that allows them to survive and reproduce better than all the others so that this new gene eventually (over hundreds of thousands of years) becomes the new norm.
I believe that when it comes to the canine diet, we are witnessing evolution in action. Rare, mutant dogs can somewhat handle the high carb diets we feed them, while the rest of the pets are sickened by them. After analyzing this study, I still think that ancestral diets are best for the majority of dogs.