Canine Nutrition Basics: Carbohydrates

The use of carbohydrates within pet food is probably the most controversial topics in pet food right now. Popular media has spent years demonizing different types of carbohydrates such as rice, corn, and even potatoes – calling them cheap-fillers, pro-inflammatory, and blaming them for a large range of diseases from obesity and diabetes to cancer. However, while carbohydrates are not strictly necessary for dogs to live, aka dogs do not have a requirement for carbohydrates, they are actually quite useful within our dog’s diet. And most of the negative press around carbohydrates is downright false, cherry-picking research studies, or presenting only half of research findings (instead of the whole picture). Let me explain why carbohydrates are used, and what their benefits can be for dogs (along with some of the drawbacks).

How Much Carbohydrates Do Dog’s Really Need?

I think the reason why there is so much confusion about carbohydrates and their role in the canine diet is that – dogs do not have a nutritional requirement for carbohydrates, whereas we do have minimal needs for protein, fats, vitamins, and minerals. And people assume that because dogs don’t need carbohydrates to survive, they shouldn’t be present in their diet.

Carbohydrates are often thought of as “functional foods” because they serve more of a functional role, rather than a required role in the diet.

Carbohydrate “Needs” are likely variable…

The ideal amount of carbohydrates for any individual dog is likely variable, and highly dependent, on other factors such as – age, activity level and medical conditions. Generally speaking a healthy, moderately to lightly active dog does well with between 50-100g carbohydrates per 1000 kcals consumed, with 2-4% crude fiber on a dry matter basis. However some dogs may do better with more or less of this amount depending on protein or fat needs, or fiber tolerance.

• Highly active dogs typically do best with lower amounts of fiber in their diet, needing sometimes less than 50g carbohydrates per 1000 kcals in order to optimize calories from fat and meeting protein needs.
• Whereas certain concurrent medical conditions – kidney disease + pancreatitis – might lead to both low protein and low fat requirements, where higher carbohydrates are needed to supply needed calories.
• For dogs who need to lose weight, we might want a moderate to high amount of fiber within the diet to help with satiety.

The Purpose of Carbohydrates

1. Carbohydrates are a source of Fiber

Fermentation of Fiber in the colon (either soluble or insoluble) produces short-chain fatty acids. We now have a large host of research looking at the role of different fiber sources (also called prebiotics) and their accompanying probiotic bacteria and their potential benefits. Certain fiber combinations have been shown to be extremely useful for the management of small and large bowel diarrhea, irritable bowel disease, and even skin conditions. There is even pending research looking at the use of prebiotic fibers and probiotics for the management of diabetes, heart disease, cancer, cognitive decline, dental health, and kidney disease. Prebiotic fibers are of particular interest because they are more stable in comparison to probiotics, thus more likely to survive storage and get to the large intestine for fermentation.

Fiber Functions:

1. Proper function of GI tract : fiber can both speed up and slow down gastric motility. Having a proper balance of fiber within a diet for your dog will make sure they are regular and have normally formed stools. Soluble fiber retains water and slows digestion, whereas insoluble fiber speeds up digestion and add bulk to stools. For dogs that have issues with gut motility (acid reflux) adjusting fiber content can be particularly useful.
2. Provides an energy source for good gut microbes: Fermentable fibers travel to the large intestine and are used as a substrate (eaten & fermented) by the good gut bacteria to produce by products called short-chain fatty acids, which supply energy to the intestines that line the digestive tract.
3. Reduced energy density of the diet: Dogs that are more inactive, prone to weight gain or that need to loose weight can benefit from higher amounts of fiber within their diet. Not only does higher amounts of fiber typically reduce caloric density, but it also has been shown to help with satiety when paired with higher amounts of protein.
4. Supports a healthy microbiome: using a variety of different types of fiber sources can help support a diverse and healthy microbiome.
5. Help with blood sugar regulation: soluble fibers form a gel within the intestine which helps regulate blood sugar, which can be particularly beneficial for dogs with diabetes.
6. Can produce Short-Chain Fatty Acids or Volatile Fatty Acids (also called Postbiotics) stimulate the gut-brain axis and can influence a variety of different systems within the body.

Ingredient	Serving Size	Total Carbs	Starch	Total Fiber	Insoluble Fiber	Soluble Fiber
Oats	1 cup	28.1	27.1	4	1.6	2.4
Brown Rice	1 cup	51.7	50	2.8	0.2	2.6
Quinoa	1 cup	39.4	32.6	8.4	5	3.4
Wholegrain Pasta	1 cup	45.5	38.5	6.3	4.1	2.2
Potato with Skin	1 medium	36.7	29.9	4.8	3.3	1.1
Wheat Bran	1/2 cup	37.4	11.3	24.6	22.6	2
Pysllium Husk	1/2 cup	32	0	28	4	24
Canned Pumpkin	1 cup	19.8	12	6.4	6.4	1.6
Blueberries	3/4 cup	15.75	0.03	1.4	0.3	1.1
Strawberries	1 cup	17.8	0.01	4.4	2.6	1.8
Spinach	1 cup	1	0	4.4	3	1.4
Kale	1 cup	0.9	0	7.2	5.1	2.1
Pear	1 medium	27.1	0	4	3.2	0.8
Apple with Skin	1 medium	23	0.08	5.7	4.2	1.5
Tomato with Skin	1 medium	3.84	0	1.3	1	0.3

Ideally we look to formulate diets with: ⅔ insoluble to ⅓ soluble

2. Carbohydrates are a source of Energy – Starch

When we say “carbohydrates are a good energy source” you might be confused. I mean fat provides a lot more calories per gram fed (8.5 kcals/g) in comparison to carbohydrates (3.5 kcals/g), so why would you use carbohydrates? It really comes down to the individual dog and their nutritional needs. There are three main instances where carbohydrates would actually be a superior form of energy for a dog in comparison to fat (or protein). 1. For Dogs who need a Low-Fat Diet, 2. For Dogs who do Sprinting activities, 3. For Dogs who need Low Residue Diets.

Low-Fat Diets

Dogs who cannot tolerate higher amounts of fat due to conditions like pancreatitis likely will not tolerate using fat as the main energy source. For these dogs carbohydrates are the next-best form of energy. The reason for this is that protein is actually a very poor energy source, and using protein as an energy source can lead to both weight loss and in some cases amino acid deficiency when essential amino acids are used as fuel instead of for essential functions within the body.

Sprinting Activities

The first five minutes of activity for dogs they use primarily carbohydrates as a fuel source, then they slowly start to up-regulate the burning of fat as fuel instead and convert to almost entirely fat oxidation at around 90 minutes. What this means is the main energy source for our dogs who do sprinting activities (not endurance activities) is carbohydrates. That said, if you create a diet lower in carbohydrates, dogs can up-regulate to start burning fat faster as the main fuel source, however, you may notice slight differences in timed sprinting activities when significantly restricting carbohydrates within a diet.

For more information on how activity level influences energy use, you can read more about active dog nutrition.

Low-Residue Diets

Diets created to be “low-residue” are typically lower in fiber, lower in fat, and highly digestible. These diets are designed to leave the stomach quickly (both fat and fiber make food stay longer in the stomach), which can help dogs who have gastrointestinal motility issues. Typically low-fiber carbohydrates and highly digestible carbohydrates are used in these cases in order to achieve this goal. This is why you might see white rice or white potatoes in some recipes for gastrointestinal diseases.

3. Carbohydrates are a source of Vitamins and Minerals

Carbohydrates can be an excellent source of certain vitamins and minerals for dogs, in particular magnesium, potassium, and b-vitamins. Whole grains are a great source of Magnesium, B-Vitamins and some are even a good source of Manganese (oats!). Potassium is typically found in our root vegetables such as potatoes, beets, and squash.

Our fruits and vegetables also contain a variety of different vitamins and minerals and are typically an excellent source of fiber, though these are typically less-dense in energy (starch).

Outside of carbohydrates, we can use certain proteins to supply these vitamins and minerals or supplementation – so carbohydrates are not the only sources by any means, however, they may be the best tolerated, or the most accessible.

4. Carbohydrates are Protein – Sparing

What does it mean by saying the Carbohydrates are “protein sparing”? Dogs do not have a nutritional need for carbohydrates, however, they do have a nutritional need for glucose. Typically for dogs fed a low-carbohydrate diet, protein is converted to glucose via gluconeogenesis within the liver in order to provide glucose for vital body functions (like the brain and other organs). Meaning that protein needs are actually higher in a low carbohydrate diet in comparison to a high carbohydrate diet because some protein (amino acids) are converted to glucose for energy.

By providing carbohydrates within the diet, we can lower the need for protein because carbohydrates can be a source of glucose for vital body functions.

Where the typical 30% protein diet may be acceptable for a diet with higher amounts of carbohydrates, typically we need closer to 40% protein for diets lower in carbohydrates in order to meet protein needs while using amino acids to create glucose.

5. Carbohydrates are used in Kibble as a binder and to cut costs

Ah, the kibble binding agent, this is the most common way I see carbohydrates negatively marketed as a filler. Saying “it’s just a filler used to bind kibble together”. The best marketing has a basis in truth. And yeah, carbohydrates are needed at about 40% DM in order to bind kibble together… Or at least at one point that was true. New technology in the manufacturing of kibble does not actually make this the case. There are now kibbled diets on the market with as little as 20% carbohydrates on a dry matter basis.

Another common statement you hear is “carbohydrates are just used by companies as a filler to cut costs” – again the best marketing has a basis in truth. Carbohydrate-based ingredients are typically a bit less expensive than meat-based ingredients. However in pet food since both are by-products of the human food industry, the cost difference isn’t as big as you think. The quality of the ingredient will change cost more than carb vs. meat within a recipe. For homemade recipes – cost may play a role as carbohydrates are typically less expensive than meat. But really, when we look at carbohydrate use within a kibble recipe – it’s usually not the main driver related to cost.

Carbohydrate Digestion

Mouth

When the dog eats their food that contains carbohydrates, the digestion of carbohydrates will start within the mouth with salivary amylase. ,However it’s important to note that dogs “gulp” their food, and there isn’t much time for digestion here. So realistically less than 2% of starch digestion occurs within the mouth.

Stomach

As the food moves from the mouth to the stomach digestion of start actually stops, this is because amylase actually requires a pH of about 6 in order to break down the bonds between glucose molecules.

Small Intestines

As our food moves out of the stomach and into the small intestine the bile from the liver is released to neutralize the pH and pancreatic amylase is released. The starch within our grains and starchy vegetables like potatoes is broken down and digested into glucose along with Lactose (milk sugar) and Sucrose (fruit sugar).

Fun Fact: When we look at Pancreatic Amylase Production of various species. Dogs produce 42-43 times as much pancreatic amylase as cats (3000 vs 70 units alpha amylase / wet weight) and dogs have twice as many glucose transport proteins as cats. Meaning they are significantly better at digesting carbohydrates in comparison to our obligate carnivore feline friends.

Blood Glucose Regulation & Storage:

Once lactose, sucrose and starches are broken down into glucose, galactose and fructose within the small intestine of the dog, they are transported out of the intestines to the portal vein. Once in the portal vein they move towards the liver where fructose and galactose are then also converted in glucose.

Blood glucose levels then rise as glucose moves all over the body to supply energy to the brain, nerves, and red blood cells. Once blood glucose levels go higher than 110 mg/dl it stimulates the pancreas to secrete insulin. When insulin is released it stimulates both the liver and the muscle cells to start to uptake free glucose and store it as glycogen. A normal range of blood glucose is 80-200 mg/dl, and currently no research

Fun fact: Cats actually have a lower ability to clear blood glucose and turn it into glycogen in comparison to dogs.

Excess glucose left over after meeting energy needs and storage needs as glycogen is stored as fat within the body (similar to excess fat and protein). Once glucose is converted to fat, it cannot be converted back to glucose (similar to excess amino acids converted to fat).

We’ve talked about times of high blood glucose, but what about when there is low blood glucose like when fasting or when consuming a very carbohydrate-restrictive diet? Once blood glucose dips below 80 mg/dl , insulin stops being triggered and instead, the pancreas starts to produce glucagon. Glucagon then triggers the liver to switch from storing blood glucose, to freeing up stored glucose.

Regardless of if a healthy dog is fed a low or high-carbohydrate diet levels of blood glucose remains within the same healthy window. No research thus far has shown that diet composition (low vs. high carb) in dogs significantly influences weight gain.

Gluconeogenesis

After about 24-48 hours without food glycogen stores within the dog start to become depleted, so the body starts to up-regulate gluconeogenesis within the dog. Basically, the body starts to break down the body’s own muscle proteins (amino acids), and those amino acids travel to the liver to be broken down into glucose. About 70% of blood glucose is produced by gluconeogenesis at the 24-hour mark, and almost 90% is produced by 42 hours.

But this can also occur if you feed a low-carbohydrate or carbohydrate-restrictive diet. The body needs glucose in order to survive. Thus if it isn’t supplied in sufficient amounts within the diet, protein (amino acids) ingested in the diet will be used via gluconeogenesis in the liver to create glucose.

Large Intestines

Any carbohydrates that are no digested within the small intestines then travel to the large intestines. Here remaining start along with fiber is broken down by bacteria to produce volatile fatty acids, short-chain fatty acids, and postbiotics. The volatile fatty acids work to feed the cells that line the intestines, where-as the postbiotics and short-chain fatty acids may influence other areas of the body through the “gut-brain axis” – similar to a hormone.

Common Sources of Carbohydrates

• Whole Grains: Brown Rice, Rolled Oats, Barley, Whole Wheat Pasta, Corn, Quinoa or Millet
• Refined Grains: White Rice, Corn Grits, White Flour, White Pasta
• Starchy Vegetables: Sweet Potatoes, White Potatoes, Beets, Butternaut Squash, Turnips, and Acron Squash
• Milk / Dairy Products: Goat Milk, Cow Milk, Cheeses
• Fruits & Vegetables

Looking for a breakdown of the different carbohydrate sources and their potential uses within a diet? – coming soon-

The Bottom Line

Though there is no nutritional requirement for carbohydrates for dogs, they are considered a “functional food” and can serve many purposes within the diet for dogs including…

1. A source of fiber & prebiotics to support the gut and microbiome
2. An alternative source of energy to fat
3. A source of vitamins and minerals
4. An source of glucose so that protein doesn’t need to be utilized to produce it.

Every dog is an individual and the amount of carbohydrates or type of carbohydrates used may vary, but carbohydrates can and do have a place in a healthy dog’s overall diet.

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