Carbohydrates
Carbohydrates, along with proteins and fats, are macronutrients. Carbohydrates consist of three different elements: carbon, hydrogen, and oxygen. They are a source of energy and fiber for dogs and cats.
Carbohydrates can be divided into monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Carbohydrates include sugars, starch, and dietary fibers. Monosaccharides include simple sugars such as glucose or fructose. Disaccharides are relatively simple sugars, such as sucrose. Both oligosaccharides and polysaccharides are considered slow carbohydrates. Polysaccharides can be further divided into two groups:
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Digestible complex carbohydrates. These are complex carbohydrates that can be digested by endogenous enzymes; these carbohydrates are called starch.
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Indigestible carbohydrates. These are carbohydrates that cannot be digested by digestive enzymes; these carbohydrates are known as dietary fibers. These fibers cannot be digested but are fermented by bacteria in the intestines.
Although FEDIAF has not established a minimum amount of carbohydrates for dogs and cats, this nutrient does have positive aspects for these animals. Simple carbohydrates and starch can be used as energy in the form of glucose. Carbohydrates are not only used for energy; they are also a source of heat for the body, as heat is released during carbohydrate metabolism. The body can also store excess simple carbohydrates and starch as glycogen or fat. Finally, certain products formed during metabolism can serve as building blocks for other nutrients.
The liver is essential for using carbohydrates as an energy source. The liver is responsible for the synthesis, storage, conversion, and release of glucose for use by other organs. The highest concentration of glycogen is found in the liver.
Carbohydrate digestion occurs throughout the body. In humans, digestion begins as soon as food enters the mouth. Human saliva contains amylase, which is necessary for breaking down carbohydrates. In dogs and cats, this enzyme is not present in saliva. In these animals, carbohydrate digestion mainly takes place in the intestines. The pancreas secretes digestive enzymes that break down a large amount of starch and sugars.
As mentioned above, the body can use carbohydrates as a source of energy. Carbohydrates provide about 3.5 kcal per gram. Certain organs and tissues (such as the brain) require glucose for energy. The body can obtain this glucose from glucogenic amino acids or glycerol from fats.
If an animal's diet contains insufficient carbohydrates, the body uses certain amino acids (normally used for milk production, fetal growth, or muscle growth) to synthesize glucose.
Carbohydrates also play an important role in pet food processing. Starch is a key component in kibble production. The gelatinization of starch is crucial for the extrusion process. Without starch, it is not possible to produce a solid kibble.
Although FEDIAF has not provided guidelines regarding carbohydrate amounts in dog and cat food, the need for this nutrient varies during pregnancy and lactation in dogs. There is an increased need for glucose to support fetal growth and lactose synthesis in milk. Generally, it is recommended to feed pregnant or lactating bitches a diet containing at least 23% carbohydrates.
Unlike dogs, cats do not require a diet higher in carbohydrates during pregnancy or lactation. Cats can maintain blood glucose levels on a low-carbohydrate but high-protein diet. Additionally, a cat’s pancreas produces much less amylase than a dog’s pancreas, making cats less capable of metabolizing large amounts of simple carbohydrates.
The bodies of dogs and cats cannot break down all carbohydrates. For example, dietary fibers are a form of complex carbohydrates that cannot be broken down. This is because their bodies do not produce the digestive enzymes needed to break the bonds between sugars in dietary fibers. Therefore, dietary fibers cannot be used as an energy source. However, fibers do have important functions in the digestive system. The indigestible fibers can be divided into two groups: fermentable fibers and non-fermentable fibers.
- In the intestines, dietary fibers are fermented mainly by bacteria and yeasts. This fermentation releases energy for the bacteria and cells of the large intestine. These fibers are known as prebiotic fibers. They support the growth of the microbiota (the total microorganisms in the intestines). In turn, the growth of microbiota prevents harmful bacteria from colonizing the intestines.
- Non-fermentable fibers pass through the intestines intact. They contribute to regular bowel movements and regulate fecal consistency. Moreover, dietary fibers contain almost no calories, providing bulk and helping to create a feeling of fullness in pets prone to overweight.
The bodies of dogs and cats produce the appropriate enzymes to digest various carbohydrates. Carbohydrates are broken down into smaller sugar units, which are then absorbed through the intestinal wall. There is one exception: lactose. Adult dogs and cats cannot adequately break down lactose, which can result in unpleasant gastrointestinal issues.
