Five years ago, I had an interesting conversation with a veterinarian friend about dog food. We were talking about diabetes in one of the dogs she was treating, and I remarked "that's what happens when you feed a carnivore carbohydrate". She gave me a funny look. At the time, I was seeing the world through the low-carb lens, and I remember thinking how bizarre it was that she didn't yield to my impeccable logic. As they say, live and learn.
The journal Nature published a fascinating paper on the evolution of the domestic dog today (1). Researchers compared the genome of wolves and domestic dogs to see what genetic changes accompanied domestication.
Humans first domesticated dogs at least 10,000 years ago, so they went through the agricultural revolution alongside us (2, 3). In other words, when we ate grains and legumes, they ate grains and legumes, at least to some extent. I've described in previous posts how humans acquired genetic adaptations to recent dietary changes (4, 5).
It is therefore fitting that the Nature article is titled "The Genomic Signature of Dog Domestication Reveals Adaptation to a Starch-rich Diet". Along with a variety of genetic changes that may impact brain development and function, they identified changes in three genes that play a key role in starch digestion and absorption. One of these genes, AMY2B, encodes pancreatic amylase, an enzyme that digests starch into glucose in the small intestine. Wolves only have two copies of AMY2B (one on each copy of chromosome 6), while domestic dogs carry 4-30 copies, suggesting that domestication has improved dogs' ability to digest starch.
This is fascinating because a similar genetic change occurred in humans. Dogs only produce amylase in the pancreas, while primates such as humans express it in the saliva in addition to the pancreas. Salivary amylase is encoded by the AMY1 gene. Chimpanzees, which eat a low-starch diet*, only have two copies of AMY1, while humans carry 2-15 copies (average ~6) (6). In other words, both humans and dogs responded to increased starch consumption with similar genetic adaptions. This is an example of a phenomenon called "convergent evolution".
It appears that my veterinarian friend was right to doubt my impeccable logic-- she knew from experience that dogs tolerate a certain amount of carbohydrate in the diet quite well. Now she has genetic evidence to back her up. Wolves may be largely carnivores, but domestic dogs tend to be omnivores-- yet another example of rapid genetic adaptation to diet.
* The diet of chimpanzees and bonobos is low in starch but not low in carbohydrate-- fruit is their main staple.