This month’s newsletter is written by Cathy B. She put together a great article from information recently published in ‘Nature’ on dogs and starch. Headlines stated that these studies show dogs have a greater ability to digest starches than wolves, but Cathy takes a careful look at the data presented to demonstrate what this really means, at least in explaining this gene and ability, and how much a starch digesting gene can affect carbohydrate digestion in a carnivore (dog).
Recently this item hit the news. Dogs have more starch digesting genes (AMY2B) than wolves, which means they can better utilize starch in their diets. They also produce longer copies of a maltase enzyme than the wolf, making it more efficient in starch digestion. This is interesting with respect to evolution and the journey of the wolf-to-dog, as they became man’s campfollower, taking advantage of the refuse heap. However, I have to wonder how much food those early humans really threw away!
The original article was published in Nature. It is a pay-per-view article and the only items you may look at are some figures and the references.
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The genomic signature of dog domestication reveals adaptation to a starch-rich diet
A mere 20 hours after its publication on the web, there were articles and blog posts about this research. One screamed that dogs were designed to eat pizza and pasta. Let us look at three science-based articles reviewing the study.
This article does a good job of summarizing the gene differences in the dog vs. wolf. http://news.sciencemag.org/sciencenow/2013/01/dog-domestication-tied-to-starch.html
"Dogs had 4 to 30 copies of the gene for amylase, a protein that starts the breakdown of starch in the intestine. Wolves have only two copies, one on each chromosome."
There is also a comment by Robert Wayne, an evolutionary biologist: "… dogs are different from wolves and don’t need a wolf like diet," he says. "They have coevolved with humans and their diet."
This article’s title claims a starchy diet led in part to the wolf to dog conversion.
"Dogs, the team found, have more copies than wolves do of the AMY2B gene, which produces an enzyme that breaks starch into easily digestible sugars." "Both brain changes and dietary adaptations were probably necessary for some wolves to be domesticated Axelsson says. Wolves that were more tolerant to stress and that didn’t run and hide at the first sign of a human would have been able to stick around garbage heaps longer and eat their fill. And those that could extract more nutrients from the plant material in early farmers’ trash would have had an evolutionary advantage."
Robert Wayne is again quoted: "The changes that allow dogs to thrive on carbohydrates while wolves eat all meat probably started with the establishment of agriculture about 10,000 years ago, and represent late steps in the domestication process, …"
In addition, this one explains things a bit more, including quotes from the paper.
"Our results show that adaptations that allowed 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 early dog domestication."
The author of the blog also makes this astounding statement: "So for those of you wondering why we feed dogs kibble instead of raw beef, here’s the reason."
So what the heck does this all mean? Is starch necessary for a dog to thrive? And what the heck is an AMY2B gene?
Basically, it is a gene that causes the body to make pancreatic amylase. Humans also have a salivary version – AMY1. However, we chew and dogs do not, so I doubt dogs will be evolving to have salivary amylase anytime soon.
Is it news that dogs digest starch? Well, no, we have known for a long time that dogs can digest starch.
There is a study from 1990 discussing the AMY2B gene, which mentions there are also copies of this gene in reproductive organs, the liver, lungs and GI tract.
The 60 dogs (14 breeds) used in the research had a range of copies of the AMY2B gene – from 4 to 30. The interpretation in the Nature paper is that the more copies of these genes in the body, the easier starch are digested. If that is true, there appears to be a wide range of starch digestibility among individual dogs.
So are these genes always working – cranking out amylase? I do not know, but I assume so. There is certainly a wide range of triggers for the "more" switch. Production of amylase can be increased (upregulated) by starvation, cortisol and T3 in sea bass. Elevated levels in dogs could be due to numerous diseases, such as pancreatitis, intestinal issues and gallstones. There also appears to be an age-related ability for starch digestion, with puppies not producing as much amylase.
In reference to the comments by scientists, frankly, I think paleontologists and evolutionary biologists ought to stick to their topic. Starchy diet is different from diet with starch present. The diet was rich in carbs only relative to the amount in a wolf’s diet, not rich in carbs period. Thriving on carbs is different from having the ability to digest them.
As for wolves only eating meat, let’s remember that wolves do have two copies of the AMY2B genes also. In a pinch, they would get something out of starchy type food. It attests to the adaptability of the wolf genome to their environment.
So what is new from the Nature article? Wolves have fewer genes for starch digestion than dogs. That is it. It does not mean that dogs need starch and should not be eating meat. It does not mean that kibble is the best food as it is largely starch. Though I am sure we will be seeing new ads soon! Paleo diet with Peas, Pasta and Potatoes! And I am sure there will be pressure from some veterinarians not to feed a raw diet or declare than dogs require carbohydrates in their diets. It also does not mean your dog can digest starch easily. She may be one of those with only four copies of the gene, thus limiting starch digestibility. So what is best for your dog? The simple thing to do is to look at the dog, your dog. What does she thrive one? What fosters good health in your dog? That is what you should feed them.
As far as I am concerned, the dinner call around here is still Beef! It’s What’s for Dinner!
by Cathy B.
AMY2B gene: http://www.ncbi.nlm.nih.gov/gene/280
Evolution of amylase genes in humans: http://cro.sagepub.com/content/4/3/503
Sea bass: http://lib.bioinfo.pl/paper:15242747
Nutrient Requirements of Dogs and Cats – on starch: http://tinyurl.com/bcw9t2c
Function of amylase: http://www.wisegeek.com/what-is-the-function-of-amylase.htm
Amylase production in dogs: http://ahdc.vet.cornell.edu/clinpath/modules/chem/amylase.htm
The Canine Genome: http://genome.cshlp.org/content/15/12/1706.full
Cathy, thank you so much for writing this article and providing such a good explanation! Your work, time and effort is greatly appreciated!!
Happy Valentine’s Day to everyone. Don’t forget to give your furry friends a special treat for this occasion . . . no, not Chocolate! Preferably something with animal protein and fat!