By Dr. Becker
Today I have a wonderful guest joining me from the American Holistic Veterinary Medical Conference in Kansas City, Dr. Doug Knueven.
Dr. Doug grew up in Cincinnati and received his veterinary degree from Ohio State University. When he graduated in 1987, he was sure he was equipped to treat all the health problems we see in today’s pets. But Dr. Doug discovered very quickly that the answers he sought for many of his animal patients weren’t contained in his college textbooks.
So after about six years practicing traditional Western veterinary medicine, Dr. Doug began delving into holistic medicine. He’s been running his holistic veterinary practice in Beaver, PA, just outside Pittsburgh, for about 20 years now.
Dr. Doug offers patients acupuncture, chiropractic, food therapy, and Chinese herbs and supplements. Like me, he is passionate about pet nutrition and feels most of the pet foods available on the market are just not healthy.
Dr. Doug has also written two books. The first, Stand By Me: A Holistic Handbook for Animals was published in 2003. In 2008 he wrote The Holistic Health Guide: Natural Care for the Whole Dog. You can find them both at Amazon.com.
Dr. Doug Reacts to Study Suggesting High-Starch Diets are Good for Dogs
The reason I asked Dr. Doug to join me today is because he wrote a really wonderful response to a study published in the January 2013 issue of the journal Nature,1 which suggests that domestic dogs have adapted to starch-rich pet foods.
I asked Dr. Doug to help interpret the study for us, because as he points out, unless you’re a geneticist, it’s difficult to grasp. He says it took him quite awhile to decipher what he thought the authors were saying. The thing that initially caught his attention, though, was the summary statement in the abstract that reads:
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.
Dr. Doug points out that the authors of the study are geneticists from Sweden. He doesn’t believe they deliberately set out to prove high-starch diets are healthy for pets. But he does think they began with a commonly held bias (belief) that “dog food is good for pets.” The problem is that when you start a study with a bias, it tends to skew your results.
So what was the study trying to prove? Dr. Doug says that it was actually a neat study. The researchers looked at the DNA of 12 wolves from around the world. Then they compared that with the DNA of 30 dogs from 14 diverse breeds. They looked for differences in the DNA – specifically, differences that also had characteristics indicating the animals were adapting to a new challenge.
Some of the differences in DNA were associated with the brain. The researchers assumed some of those differences were related to differing levels of aggressiveness between domestic dogs and wolves, which makes sense.
Study’s Focus Is on Genes Associated with Digestion in Domestic Dogs and Wolves
What the researchers were really focused on, however, were the genes associated with digestion. They describe three major steps in the breakdown and absorption of starch in dogs.
The first step involves the enzyme amylase; the second step involves the enzyme maltase-glucoamylase; and the third step involves a transport protein called sodium-glucose transporter 1, or SGLT1. SGLT1 transports glucose from the intestinal lumen into the body. The researchers looked at these three steps from a genetic standpoint.
What they found with regard to step one, was that there are between 4 and 30 copies of the gene that codes for amylase in dogs, as compared to only 2 copies in wolves. They assumed this means dogs are better able to handle starch. To prove that assumption, they looked at blood samples from the animals to determine the expression of the amylase gene. They discovered the expression of the gene was higher in dogs than wolves, and the levels of amylase in the blood were higher in the dogs than in the wolves. And that’s where they left it.
That sounds pretty convincing, so I asked Dr. Doug for his perspective on what those results really mean. He says that while the researchers did show the dogs have more genes coded for amylase than wolves, they didn’t explain the significance of the finding. What if a real omnivore (an animal designed to eat starchy foods) has 10,000 genes coding for amylase? In that case, 4 to 30 genes isn’t significant. But the study doesn’t go that far.
As for the expression of the amylase gene and the enzyme level in blood samples, Dr. Doug points out that those measures are dependent on the diet the animal is eating. We know from the study of nutrigenomics that an animal’s body can adapt to its diet by turning genes on and off, altering the expression of those genes.
Wolves eat a diet high in meat, so it makes sense that their amylase genes are turned down. There won’t be many of those starch-processing enzymes in the bloodstream because Mother Nature knows better. By contrast, domestic dogs fed a high-starch diet will have those genes turned on. So as far as Dr. Doug is concerned, that part of the study was essentially meaningless.
Study Bias in Favor of High-Starch Diets Leads to Faulty Assumptions
In step two the researchers looked at gene coding for maltase-glucoamylase, which is the second phase in the breakdown of dietary starch. Interestingly, they didn’t find a high number of genes, and it was almost like they thought, “Darn, that one didn’t work.”
What they did find was that the gene in the dogs was mutated away from the gene in the wolves. According to the researchers, that mutation made the gene more comparable to the gene of an omnivore than a carnivore. They took things further by testing the blood and also the pancreas for levels of maltase-glucoamylase and – no surprise – they found higher levels in the dogs than in the wolves. But in this instance they did acknowledge the difference might be explained by nutrigenomics, with the genes turned on in the dogs eating starch, but not in the meat-eating wolves.
It’s almost as if the study authors took one approach in step one, and another approach in step two. For example, in step one, the number of genes was important, but it wasn’t in step two. In step two, the effect of nutrigenomics might explain differences in enzyme levels in the blood, but there was no mention of nutrigenomics in step one.
The third step involved the transport protein SGLT1 that moves the end product, glucose, from the lumen of the gut out into the body. As in step two, the researchers found not a higher number of genes, but a change or mutation in the genes. And that’s all they found – that the gene was different in the dogs than in the wolves.
So they made the assumption that the mutated gene means dogs are better able to transport glucose into the body than wolves. Because, of course, dogs thrive on a high-starch diet, so obviously that’s the conclusion you must arrive at. (This is how starting a study with a bias skews results.)
Dr. Doug believes the results in step three also have to do with how dogs are able to adapt to the diet they are eating. The gene is different, but that doesn’t necessarily mean it is better at transporting glucose across the barrier.
What the Study Proves: Dogs Can Adapt to Biologically Inappropriate Diets
As you might expect, the Nature study was picked up and heavily promoted by pet food companies selling grain-based formulas. It’s frustrating to see a study that really proves nothing, used by pet food companies as proof that starch-rich diets are good for dogs.
All the study validates is that a dog’s body has some capacity to adapt to the food it eats. It certainly doesn’t prove that it’s good for dogs to have more starch in their diet. I certainly don’t want to encourage people to feed biologically inappropriate diets because their pet’s body will adapt. I want people to feed their pets what nature designed them to eat. Then their bodies don’t have to work to adapt to their diet.
Dr. Doug points out that the study does also show there are genetic differences between dogs and wolves, which shouldn’t be a surprise to anyone. He feels that dogs are undergoing an evolutionary process right now, but what some people might not understand is that no individual dog evolves. Feeding dogs a grain-based diet won’t cause them to evolve to change their genetic code to be able to handle it better.
The way evolution works is, there are certain “mutant” individuals – let’s say a group of dogs that have a mutation that allows them to digest starch better than most dogs. Those individuals will do fine on a high-starch diet. They will reproduce, which means the mutated gene they carry will become more common in the future. But all the rest of the dogs will continue to not do well on a high-starch diet. The dogs with the mutated gene can survive on it, but the “non-mutants” don’t do well, and that can lead to problems, including the biological consequences of feeding an inappropriate, high-starch diet to a carnivore.
Dr. Doug finds it interesting that the study authors didn’t address what happens after the glucose in those high-starch diets hits the dogs’ systems. We both understand the kind of inflammatory processes that take place.
He went on to say he recently discovered that the endocrine system has adapted primarily to a diet low in starch vs. high in starch. It becomes obvious when we realize there are eight different hormones that address trying to get more glucose into the blood (adrenalin, the glucocorticoids, glucagon, growth hormone, vasopressin, melanocyte stimulating hormone, thyroid stimulating hormone, and norepinephrine), but there’s only one hormone – insulin – that can lower blood glucose levels. So the endocrine system, which is set up to monitor our metabolism, is clearly designed for low starch diets.
Humans are omnivores, and so we try to feed starch-rich diets to our carnivorous pets. In my view, cats are obligate carnivores and dogs are scavenging carnivores. Dogs can certainly tolerate a higher amount of dietary starch than kitties, but it’s still a metabolic stressor for them, including the fluctuation in hormones.
As Dr. Doug points out (and it’s something I also talk about all the time), there’s a difference between surviving on a diet and thriving on a diet. He says the use of “thriving” in the study summary quote above really drives him crazy.
My Sincere Thanks to Dr. Doug Knueven
I want to thank Dr. Knueven for chatting with me today and breaking down the Nature study into something comprehensible. Not only did he make it understandable, but his thoughtful response will help people who feed a species-appropriate diet understand that what the study proves is simply that dogs can adapt to whatever diet they are fed.
And while there are some genetic differences that have evolved between wolves and domestic dogs, it’s not an argument for feeding grain-based diets to carnivores.