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It's almost criminal that it has taken me so long to cover this topic directly.
I actually came to write about it in a roundabout way. Early this morning I was about a thousand words into an article about the link between canine cancer and canine obesity -- be on the look-out for that one, by the way, it covers some really compelling new research -- and I found myself referencing the process through which dietary carbohydrates and the hormone insulin lead to fat growth.
Rather than describe the entire process, I thought I'd just link to a previous post in which I'd summarized it. And only then did I discover that no such post existed. While I've written a lot about canine obesity and a lot about carbohydrates, I've never directly spelled-out how the latter contributes to the former. I've never written an article explaining the biochemical process by which carbohydrates make dogs (and people) fat.
Anyone who understands the primary biochemical argument behind the Paleo diet, the Atkins diet, the keto diet, or any other very low-carb diet can probably just skip this post.
But if you're not already familiar with how carbohydrates make dogs (and people) fat, then this one's for you. I've endeavored to make my explanation as simple as possible (though no simpler) and then tacked-on a bunch of useful links at the end, in case anyone wants to go further down the rabbit hole.
Carbs come in lots of forms. But once they find their way into your dog's digestive system, more or less all dietary carbohydrates get converted into a single kind of sugar molecule called glucose.
These glucose molecules then get pumped out of the digestive tract and into your dog's bloodstream. Some carbs get converted to glucose really rapidly (resulting in spiking of blood glucose levels), others more gradually. But, for all intents and purposes, they all end up as glucose.
Now, we all know that bodies are made up of cells and that those cells need energy to function. The process by which cells convert circulating molecules into usable energy is called metabolism. Along with other kinds of molecules like fatty acids and ketone bodies, blood glucose is one of several sources of metabolic fuel that your dog's cells can use to power themselves along while performing their respective functions.
In fact, when it comes to understanding obesity, glucose is a particularly important fuel source, for two different reasons:
1) Glucose is the "preferred" source of fuel for most of your dog's cells.
This does not mean that your dog needs to ingest dietary carbohydrates in order to keep her cells doing their jobs. As I've explained elsewhere, dietary carbohydrates are not a necessary ingredient in your dog's diet.
What it does mean is that if those cells have a choice between glucose and some other forms of fuel (because blood glucose happens to be plentiful), they'll tend to use the glucose first.
This is important when it comes to understanding obesity because when cells are burning glucose for energy they generally aren't burning stored fat reserves for energy. And, obviously, burning those fat reserves for energy is the cornerstone of any weight-loss process.
2) Glucose is toxic.
This is something that anyone who has brushed up against diabetes already knows. If your dog's blood glucose levels get too high, it will result in death. It's that simple.
Fortunately, properly-functioning canine bodies have a handy mechanism for dealing with high levels of toxic blood glucose. When glucose is detected in the bloodstream (in fact, even before it's detected -- this process has been shown to begin when human beings merely think about carbohydrate-rich foods), the hormone insulin gets secreted by the pancreas.
Insulin performs all sorts of important roles in the body. But one of them is particularly relevant to this topic: it tells cells in the muscles, liver, and fat tissue to effectively "open up" and suck in any excess circulating glucose. As those cells absorb the excess blood glucose (which they convert into other, more stable molecules and store), blood sugar drops back down to tolerable levels.
Phew, crisis averted. Great, right?
Well, not so fast. Turns out that the cells in the liver and muscles can only store so much glucose. And once they reach maximum capacity, as they do rather quickly, there's only one place for the excess blood glucose to go -- directly into fat cells.
The fat cells slowly grow as they mop up more and more blood sugar. And that growth, of course, is relevant to understanding how obesity works because it is, literally, the process of getting fatter.
As this process gets repeated over and over again it gives rise to unhealthy second-order effects too. Insulin receptors become less sensitive, blood sugar levels go up, and it becomes easier and easier for fat cells to grow. And, of course, there are subtleties and exceptions that I'm glossing over for the sake of brevity. But for the most part, here's all you need to understand about how dietary carbohydrates make your dog fat:
Dietary carbs beget glucose. Glucose begets insulin. And insulin begets the retention and/or growth of body fat.
None of this is remotely controversial. It's all there in any textbook on nutrition and metabolism.
And it's pretty surprising that, in light of all this, Big Kibble continues to churn out carb-stuffed dog food products (according to the NRC, carbohydrates are the primary macronutrients in most kibble-ized dog foods) and then tell us all that those products are "healthy" and "natural."
It's only a little less surprising that so many of us (including many veterinarians) have been duped into accepting the false wisdom that "healthy whole grains" and other carbohydrates are a normal part of a "balanced" canine diet.
But, in light of all this, what's not remotely surprising is that more than half the dogs in America are overweight or obese.
The Recommended Reading Rabbit Hole:
-- Gary Taubes and Co. at the NuSi have compiled and summarized every published study done over the past 70 years with any relevance whatsoever to the issue of how bodies get fat. If you like to get your data from original sources, this is the only logical place to start.
-- Instead of sifting through the NuSi research yourself, you could always just pick up a copy of Taubes's Why We Get Fat (or, if you've got the appetite for 600+ pages, his longer volume Good Calories, Bad Calories) and simply let him explain it all to you. Taubes is a journalist, not a clinician. But he is very rigorous.
-- While you're at the book store, grab a copy of Dr. William Davis's superb bestseller Wheat Belly. Davis is a clinician, not a journalist. But he writes very clearly.
-- If you prefer a shorter, shallower kind of rabbit hole, Davis and Taubes both have blogs. Additionally, Mark Sisson's "Definitive Guide" to understanding Type II Diabetes and the processes described above is written so clearly that even Kody would probably understand it. Other paleo guys like Robb Wolf, Loren Cordain, and Chris Kresser also hit these topics regularly on their blogs.
Be on the look-out for the cancer/obesity article early next week. For now, Kody and I are heading out to enjoy the killer spring weather. I hope you're all having a great weekend too.
[Like this post? Want to learn more about how to keep your dog healthy and happy? Check out Dogs, Dog Food, and Dogma, my book from Present Tense Press. Kirkus Reviews calls it "remarkable," "eye-opening," "scandalous," and "impressive."]