Canines and Carbohydrates

Canines and Carbohydrates – a Conundrum?

A long-standing debate in the canine community concerns the significance of carbohydrates in a dog’s diet. Carbohydrates are one of six essential nutrients and provide dietary energy. This classification encompasses simple sugars like glucose and more complex molecules like starch, as well as fibrous carbohydrates such as cellulose, a structural component of plants. These different forms of carbohydrates have distinct physical, nutritional, and digestive properties.

In this article, we will examine the role of carbohydrates in a dog’s diet, including whether they are necessary, whether dogs can digest them, and review current evidence on the subject.

Carbohydrate is how plants store energy. Grain crops are important food ingredients and sources of carbohydrate.

What are Carbohydrates?

Carbohydrates are a diverse group of substances that contain the elements carbon, hydrogen, and oxygen. Ranging from simple, small molecules such as glucose to large, complex polymers like cellulose, which is the most abundant polymer on the planet, carbohydrates are the major energy-containing substances in plants, comprising up to 90 percent of plant dry matter content, and are also a significant source of dietary energy.

Carbohydrates are classified as monosaccharides, disaccharides, and polysaccharides. Monosaccharides are the simplest form of carbohydrates and are often referred to as simple sugars. Key monosaccharides include glucose, fructose, and galactose. Disaccharides are formed when two monosaccharide units are joined together, with lactose being a disaccharide found in milk and consisting of one glucose molecule joined to a galactose molecule. It is worth noting that adult dogs lack the enzyme lactase needed to break lactose into its component monosaccharide parts, making them effectively lactose-intolerant and susceptible to digestive upset if they consume lactose. Other common disaccharides include maltose and sucrose, which is the sugar commonly added to tea and coffee.

Sucrose is more commonly known as table sugar and milk contains the sugar lactose.

Polysaccharides are complex carbohydrates composed of individual monosaccharides linked together to form long chains. These carbohydrates serve as either energy-storage forms, such as starch, or structural forms, such as cellulose. Glycogen, the storage polysaccharide found in animal tissues, is crucial for maintaining normal energy levels in the body, particularly during times of high energetic demands. Dogs have low levels of glycogen naturally, and targeted nutrition can support its replacement after exercise.

Simple carbohydrates are easily digested, absorbed, and utilized as an energy source, while larger, more complex carbohydrates require specialized digestive systems and processes for digestion. Although dogs can digest starch, they lack specific adaptations for digesting most fibrous forms of carbohydrates. However, some fibrous carbohydrates are not digestible but remain valuable from a digestive health perspective. Therefore, overly simplistic statements that dogs do not require carbohydrates are problematic because not all carbohydrates are created equal.

Do Dogs Need Carbohydrates?

It is commonly stated that dogs are unable to digest carbohydrates. This has led to the assumption that carbohydrates are not necessary in a dog's diet. However, it is important to note that this topic is not as straightforward as it may seem. There are various nuances to consider, as is often the case in biology.

While it is true that dogs do not have a minimum dietary requirement for carbohydrates, there are situations in which carbohydrates can be beneficial. For example, pregnant and lactating bitches require carbohydrates to support the nutritional demands of reproduction. Additionally, some highly active dogs may benefit from carbohydrates to aid in performance and recovery.

To gain a comprehensive understanding of the relationship between dogs and carbohydrates, it is necessary to examine carbohydrates in terms of their chemistry, nutrition, and digestive health. It is also important to consider their value in terms of ingredient supply, environmental sustainability, and other factors that impact the nutrition of our dogs.

The Simple Carbohydrates – the Sugars

Glucose is a fundamental simple carbohydrate that plays a pivotal role in supporting the overall functioning and efficient metabolism of the body. It serves as the primary endpoint of all digestion and is the carbohydrate present in the bloodstream. Notably, glucose is essential for the brain as it requires a consistent supply to sustain normal neurological function.

Glucose is the end point of all digestion and is critical to support blood-sugar levels and normal nervous system functioning.

A supply of simple carbohydrates can be beneficial for highly active, sporting or working dogs that are expected to perform at a high level on consecutive days. These dogs may deplete their liver and muscle stores of glycogen, and dietary carbohydrate can aid in replenishing those stores. Glycogen is a crucial energy source when respiration and associated biochemical and cellular pathways are challenged in their ability to generate energy for the animal to function. In such cases, glycogen is broken down into glucose molecules that can then be used as a source of 'fuel' by cells to support cellular work, which translates into the activities we ask our dogs to perform.

However, excess simple, soluble carbohydrates can be problematic as they can be converted to fat if not metabolized by the body. They can also cause issues for normal, healthy organ functioning, such as the pancreas. Excessive and sudden intake of soluble carbohydrates can also lead to digestive upset and loose stools in many dogs. Therefore, it is essential to be cautious with the dietary supply of these carbohydrates.

Complex Carbohydrates – the Polysaccharides

Complex carbohydrates are large molecules composed of many monosaccharides linked together in long chains. The digestibility of these chains is determined by their structure. Common complex carbohydrates include starch, glycogen, and various forms of dietary fiber, such as cellulose. Starch is a significant source of stored energy found in cereals. It requires enzymes to break down the bonds between individual subunits, and amylase is a key enzyme produced by dogs. Conversely, dietary fiber is not easily digested by dogs directly. However, intestinal microbes can digest some fiber through a process called fermentation. Some types of fiber are highly fermentable and more easily digested by gut microbes. Soluble fibers mix with fluid in the digestive system and form a gel-like substance, which tends to be highly fermentable and can increase the speed of material through the digestive system. Many soluble fibers are useful prebiotics that support the health of the gut microbiome. Insoluble fiber is much less fermentable and can help slow digestive transit and increase fecal size. Cellulose, the major structural carbohydrate in plants, has very low solubility and fermentability. As a result, much of the plant material consumed by dogs appears to pass through the digestive system unchanged, with grass being a particular culprit.

The Dog’s Dietary Requirement for Carbohydrates

Let us examine the dietary needs of dogs and their requirement for carbohydrates. Unlike other essential nutrients such as protein, fat, vitamins, and minerals, there is no recorded minimum dietary requirement for carbohydrates in dogs. This leads to the common assumption that carbohydrates are not necessary in a dog's diet.

Dogs have a unique biochemical process called gluconeogenesis, which occurs primarily in the liver. This process allows dogs to synthesize glucose from non-carbohydrate precursor molecules, such as protein. While obligate carnivores like cats have high levels of gluconeogenesis, domestic dogs are more omnivorous in their feeding habits but still possess high levels of this process. Therefore, if a dog's diet supplies adequate levels of substances that can be used as precursors for gluconeogenesis, such as protein, then dietary provision of carbohydrates is not strictly necessary.

However, carbohydrates do offer specific benefits for dogs. They can be used as an energy source, which has a "protein-sparing" role, allowing dietary protein to be used for other essential body functions such as growth. This could have metabolic benefits and be positive for wider environmental sustainability. Additionally, dietary carbohydrates can be extremely useful during pregnancy, lactation, or for highly active or sporting dogs.

Before considering the potential benefits of dietary carbohydrates, it is important to consider whether dogs can digest them.

Can Dogs Digest Carbohydrates?

If there is no apparent minimum requirement for carbohydrates in the canine diet, it is important to understand why they are often included in formulated diets and whether dogs are capable of digesting them. The answer is not straightforward, as some carbohydrates are easily digested and absorbed, while others pose a greater challenge. To determine whether dogs can digest dietary carbohydrates, it is necessary to examine how their digestive system processes the various forms of carbohydrates found in dog food, including seeds, grains, potatoes, sugar beet, and other potential ingredients.

Digesting Simple Carbohydrates

Simple carbohydrates, such as glucose and sucrose, are easily digested and absorbed in the small intestine. However, some require specific enzymes to aid in their digestion. For instance, adult dogs lose the ability to digest milk sugars after weaning due to their lack of lactase enzyme. Consumption of foods containing milk sugar may cause flatulence, digestive upset, and diarrhea in dogs.

Dogs have taste receptors to detect sweet flavors, which may explain their taste preferences for certain sweet-tasting foodstuffs. However, this could also lead to accidental consumption of toxic human foods such as chocolate and artificial sweeteners like xylitol, which is extremely dangerous for dogs. Furthermore, dogs may show a preference for young, fresh grass and other plants that are rich in sugars.

In conclusion, dogs can digest and absorb many simple carbohydrates.

Digesting Fibrous Carbohydrates

Fibrous carbohydrates are a significant component of plant structure and are present in the outer casings of seeds and grains, such as bran. However, dogs possess limited digestive capacity when it comes to fibrous carbohydrates. It is well-known that dogs cannot digest large, complex, and fibrous forms of carbohydrates, such as cellulose, as evidenced by their consumption of grass, vegetables, or other plant material. Unlike grazing species such as cattle and horses, dogs lack specialized digestive systems to digest fibrous carbohydrates. Ruminants, such as sheep, goats, and cattle, have evolved a highly specialized digestive organ, the reticulorumen, which is a large microbial fermentation chamber. This chamber contains a vast population of microorganisms that can digest fibrous plant material and derive nutritional value from it. These microorganisms are cellulolytic and can break down cellulose into its molecular building-blocks.

In comparison to horses and cattle, dogs have a very low ability to digest fibrous carbohydrates.

Horses possess a modified digestion system that allows them to digest plant material through their enlarged caecum. This caecum serves as a microbial fermentation vat of cellulolytic microorganisms that can break down and utilize plant material as a source of energy and nutrients. In contrast, dogs and humans have a smaller and less significant caecum, resulting in limited capacity to digest fibrous plant material and use it as a source of energy.

Upon consumption of structural and fibrous carbohydrates, dogs' digestive tract leaves them unchanged in shape, size, or color before being excreted. To reduce their size and visibility, these complex carbohydrates are sometimes pre-processed before being included in dog food. Although undigested by the dog's digestive system, fibrous carbohydrates have health benefits for dogs. Dietary fiber supports digestive system health and function, bulks out faeces, empties anal glands, and acts as a prebiotic by feeding the microbiome. This population of microorganisms within the digestive system is increasingly recognized as important for overall health. Therefore, while dogs cannot digest fibrous carbohydrates, they are valuable in their diets to support microbiome and digestive health.

Digesting Starch

In comparison to cellulose, there exist additional types of complex carbohydrates that can be digested and utilized by our canine companions. Starch is composed of two distinct forms, namely starch-amylose and starch-amylopectin. Both of these forms are composed of lengthy, repetitive chains of individual units that are connected together, differing solely in their molecular structure and the chemical bonds that hold these building-blocks together. In order to facilitate digestion, the chemical bonds between individual subunits must be broken down, necessitating the use of specific enzymes.

Many northern dog breeds, such as these sled dogs, appear to have a lower capacity for starch digestion compared to spaniels, for example.

Amylase is an essential enzyme required to break down the molecular bonds between the subunits of starch-amylose. It is naturally present in the saliva of many species, where it initiates the digestive process of breaking down dietary starch. Subsequently, amylase is produced in other organs such as the pancreas, and the process of starch digestion continues throughout the digestive system.

Although dogs do not possess significant levels of salivary amylase, research has demonstrated that they do produce amylase in other parts of their digestive system, notably from the pancreas. Therefore, dogs have the digestive capacity to digest the amylose form of starch and derive nutritional benefits from it. However, it is important to note that there is a breed difference in the capability of dogs to digest starch. For instance, huskies and northern breeds appear to have less capacity than springer spaniels, likely due to selective breeding.

Low-Carbohydrate Diets for Dogs

Due to concerns about feeding carbohydrates to dogs and a growing interest in diets that align with ancestral canine eating habits, many caregivers are opting for low-carbohydrate diets. These diets contain minimal grains or plant materials and can be beneficial for some dogs' health and performance, particularly high-endurance breeds that perform better on high-fat, low-carbohydrate diets. Additionally, certain health conditions may benefit from managed carbohydrate levels. In response to caregiver demand, the commercial dog-food industry has developed grain-free diets, which have seen significant sales growth. However, it's essential to note that these diets may still include carbohydrates, such as potato or sweet potato, for production or formulation reasons, and their digestibility and nutrient bioavailability may differ from more traditional dog-food ingredients. Furthermore, some alternative ingredients may be linked to heart problems in dogs, such as dilated cardiomyopathy (DCM), and ongoing research is exploring the nutritional and general causative factors of these issues.

Summary

• Carbohydrates are a major source of dietary energy and come in various forms, from simple to complex.
• Dogs do not have a minimum dietary requirement for carbohydrates as they can produce their own, but pregnant, lactating, and active dogs may benefit from additional dietary carbohydrates.
• Simple carbohydrates, such as glucose, are easily and quickly digested and absorbed by dogs and provide a good source of energy.
• Fibrous carbohydrates found in many plants are not digestible by dogs but may be beneficial for digestive health.
• Dogs can produce the digestive enzyme amylase, which means they are capable of digesting starch carbohydrates.
• Grain-free dog foods are not necessarily carbohydrate-free - they often contain alternative sources of carbohydrates.