[This article is part of our "Evidence Round-Up" series, the purpose of which is to explain what published, peer-reviewed scientific papers and other credible evidentiary sources have to say about common nuggets of canine health and fitness "wisdom." If there's a topic you'd like to see covered in the next installment of the series, please let us know.]
Most dog food products are composed largely of carbohydrates like cereal grains, corn, potatoes, and rice. And many purveyors of conventional wisdom (not to mention most dog food manufacturers) would have you believe that carbohydrates play an important role in a "balanced" canine diet and that it makes perfect sense for your dog to suck down a few hundred grams of carbs a day. You've probably heard those folks tell you that carbs provide our dogs with the metabolic energy they need to power exercise and their other daily physical activities. And if you want to make sure that your dog doesn't "hit the wall" and keel over mid-walk, the thinking goes, you need to keep a steady stream of carbs flowing through his body at all times.
On the other hand, many advocates of low-carb and "paleo"-style human diets have in recent years become increasingly vocal in their insistence that carbohydrates have no place in a proper canine diet. These folks not only reject the conventional wisdom concerning the nutritional benefits of carbs but in many cases even vilify carbs altogether, painting the modern-day carb-heavy diet to be an unfortunate byproduct of marketing propaganda and a leading cause of the canine obesity epidemic.
A contentious issue. Two competing factions. A witches' brew of half-reasoned opinions and misinformation. Sounds like the perfect subject for an "Evidence Round-Up"!
Okay, so what does the evidence say---do dogs need carbohydrates in their diet or not?
Let's start by dealing with a threshold issue that is really so obvious that it only warrants only a cursory treatment here: dogs undoubtedly can subsist on a carb-heavy diet. For evidence supporting this claim, all you really have to do is stroll down the dog food aisle at your local Petsmart. The gross majority of packaged dog food products are composed largely of carbohydrates. And the millions of pets that consume those products exclusively, day in and day out, are living proof that dogs certainly can digest and draw energy from ingredients like cereal grains, corn, and rice.
For a more sophisticated-sounding reason for believing this, you can always cite this much-ballyhooed* study, published in the esteemed journal Nature earlier this year. Using genomic resequencing technologies, the paper's authors showed that one of the few genetic differences between dogs and wolves is that dogs have evolved the ability to digest starches while, for the most part, wolves have not. They go on to suggest that this adaptation arose from the development of agriculture and contributed to the close relationship that humans and domestic dogs today enjoy.
But the Nature study is only relevant to the issue of whether dogs can tolerate carbs in their diet. What it doesn't discuss is whether dogs need carbs in their diet.
This distinction is important. Because whether dogs can tolerate carbohydrate doesn't do much to inform the discussion of what the optimal canine diet should be. But whether they require carbohydrate certainly does. The argument that carbohydrates are one of the root causes of the canine obesity epidemic, for example, never really gets off the runway if dogs must have carbohydrate in their diets in order to survive and thrive.
To understand whether dogs do in fact require carbohydrates in their diet, the only logical place to start is the "Nutrient Requirements of Dogs and Cats." Published by the National Research Council of the National Academies, the NRDC is the Bible of canine nutrition. It's the single most authoritative research compendium on the topic in existence today. Every veterinarian worth her salt has a copy sitting on the bookshelf in her office.
The NRDC defines the ideal canine diet by setting forth all manner of evidence-based daily minimum allowances for vitamins, minerals, and macronutrients. So you would expect that, if carbs were a necessary part of your dog's diet, the NRDC would clearly articulate a daily minimum requirement saying so.
Well, in short, it doesn't.
That's right, while the Bible of canine nutrition clearly defines the minimum amount of fat, amino acids, vitamins, and minerals your dog should be ingesting, it does nothing of the sort with regard to carbohydrates.
In fact, it explicitly declares that carbohydrates are not a necessary part of an optimal canine diet:
"Thus, there appears to be no requirement for digestible carbohydrate in dogs provided enough protein is given to supply the precursors for glucogenesis."
In light of all the noise made by advocates of the conventionally-understood "balanced" canine diet, this sounds hard to believe. But it's right there in the Bible of canine nutrition. In fact, in making this point, the NRDC discusses scores of studies in which dogs were fed diets composed entirely of fats and proteins and suffered no ill effects whatsoever. Most pointedly, it cites numerous examples in which sled dogs, the uber-athletes of the canine world, trained and competed in ridiculously grueling events while being fed diets containing only proteins and fats. Despite the fact that these animals were running the equivalent of several marathons every day (while towing heavy sleds) for extended periods of time, they did just fine without carbs. Most of the studies discussed in the NRDC concluded that the amount of fed carbohydrate had no impact on overall physical performance. But some actually concluded that dogs ran longer, faster, and better on diets containing little or no carbs.
Now, this all makes perfect sense when you consider your dog's evolutionary history. Wolves don't eat carbohydrates. At all.** As the Nature study shows, they can't even digest them effectively. And yet it has been shown that wolves travel more than 26 miles (a complete marathon) between kills. (The studies from which this number comes are not available online. But they are discussed on page 119 of "Wolves: Behavior, Ecology, and Conservation," the leading research compendium on the behavior and physiology of wolves.)
Obviously, wolves have evolved a way of metabolizing long-term energy from a source other than carbohydrates. And regardless of whether dogs have also evolved the alternative ability to metabolize carbs for energy (as the Nature study shows), they definitely have retained the ability to create energy from that other source (the Nature study actually demonstrates this as well by not discussing any such difference between dogs and wolves).
So what is this other energy source that sled dogs and wolves use to power themselves through their marathon-a-day lives? Here's a hint: It begins with an "f," ends with a "t," rhymes with "rat," and is overabundant in the bodies of most dogs in America. Get where we're going with this?
Trust us that we've got plenty more to say about the canine metabolic process of fat oxidation and its role in canine weight-loss. But that's a topic for another day. For now just focus on the what the published scientific literature and other valid evidence has to say about whether your dog's diet needs to contain carbohydrates: In short, it doesn't.
* It should be noted that this study was widely misinterpreted by the popular media. Sources such as NPR reported it as evidence that dogs evolved to "love" carbs, suggesting that carbohydrate should therefore play a prominent role in the optimal canine diet. In truth, that conclusion goes far beyond what's actually shown in the paper. A more appropriate headline would have been "In Order to Live With People Canines Evolved to Tolerate Starchy Foods." It's beyond the scope of this article to explain why this is not a trivial distinction. But trust us, it isn't.
** It is a common misconception that wolves ingest plant-based carbohydrates in significant quantities because they ingest the contents of their prey's stomachs. This is a reasonable-sounding theory, until you remember that wolves are unable to effectively digest starches (per the Nature study). Rolf Peterson and Paolo Ciucci (two leading wolf researchers) estimate that only 1.7% of a wolf's daily calories come from carbohydrate sources. And here's what they have to say about the topic: "The vegetation in the intestinal tract is of no interest to wolves ... Sometimes the rumen contents, with or without the surrounding rumen, freeze and become one of the few signs left of a kill in winter."