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The gastrointestinal tract is the source of nutrient absorption, making it integral to overall health. Therefore, feeding your cat for optimal digestive health is key for a healthy cat. Research shows fiber, prebiotics, probiotics, antioxidants and fatty acids are important in maintaining gastrointestinal health.

Fiber
The addition of fiber at optimal levels in a diet is essential for the normal function and health of the gastrointestinal tract.

Dietary fibers are plant carbohydrates which cannot be digested by mammalian enzymes. These structural plant carbohydrates include pectin, lignin, cellulose, hemicellulose, muclinage, and gums. Different types of fibers have varying levels of solubility and fermentation; this ranges from pectin which is highly fermentable, to beet pulp which is moderately fermentable, to cellulose which is non-fermentable. Non-fermentable fibers helps with satiety, maintenance of a normal intestinal transit time and gastrointestinal motility as well as increasing diet bulk. Fermentable fibers, on the other hand, are fermented to short chain fatty acids by bacteria in the colon and have variable effects on gastric emptying. Moderately soluble fibers have been linked to increased colon weight as well as an increased mucosal surface area for absorption of nutrients.

Fiber, though it is not an essential nutrient, is important for a healthy gastrointestinal tract. The microbes found in the cat’s large intestine have the ability to ferment dietary fibers to short chain fatty acids. Cells of the gastrointestinal tract are constantly dying and being replaced by new cells, which requires a lot of energy. The fatty acids produced are used as energy sources for these epithelial cells which line the gastrointestinal tract. As a result of the presence of energy from the fatty acids, colonic cell proliferation is increases.

Short chain fatty acids production from dietary fibers have many other advantageous effects on the gastrointestinal tract. They increase motility by stimulating rhythmic contractions of the distal portion of the small intestine, which potentially decreases fermentation in the small intestine while increasing it in the large intestine for further fatty acid absorption. Blood flow to the colon also increases with the presence of short chain fatty acids. These fatty acids also increase sodium absorption which helps maintain normal electrolyte and fluid balance in the intestine, reducing the risk for diarrhea . These homeostatic conditions of the intestinal tract promote the growth of beneficial bacteria while inhibiting the proliferation of pathogenic ones. A healthy and balanced gut microbiome is important for maintaining a healthy digestive tract.

Fibers promote bacterial growth and activity in the large intestine. It is essential for a healthy gastrointestinal tract to have a healthy and stable gut microbiota. The microorganisms present in the colon are responsible for the fermentation of the fiber into short chain fatty acids and for the production of some vitamins.

Prebiotics
Prebiotics are short-chain carbohydrates classified as fibers with an added aspect as they selectively promote the growth of beneficial bacteria. By promoting the health and proliferation of beneficial bacteria, they suppress the growth of pathogenic ones by outcompeting them. Insulin, galactooligosaccharides, lactulose, fructooligosaccharides (FOS) and mannanoligosaccharides (MOS) are all examples of prebiotics.

Probiotics
Probiotics are becoming increasingly popular in the diets of felines. They are included in the diet to increase the number of bacteria and microbes that are normally present in a healthy gut. Probiotics are considered a supplement rather than part of nutrition. Therefore, there are no strict regulations to the amount of probiotics that should be included in foods. The function of probiotics goes beyond basic nutrition and has many benefits to the health of the organism. The use of probiotics can help in the prevention and treatment of certain diseases or disorders of felines. Examples include prevention of allergies, diarrhea, symptoms relating to stress, etc. . The health of the cats is very much dependent on the fermentation that occurs through gut biota. The gut biota has an important role in the metabolism, absorption, and protective functions of the gastro intestinal tract. Felines have different gut bacteria than canines. However, the most common biota that are found in both felines and canines are Firmicutes, Bacteroidetes, Proteobacteria, and Fusobacteria . Although these are the most common types of gut biota found in felines, there are variances between independent cats. Each cat has their own unique and independent number and type of gut microbes.

Antioxidants
Nutraceuticals such as antioxidants are considered to be additives of gastrointestinal diets to prevent digestive upset. Antioxidants have the ability to remove free radicals from the body which can cause damage to cell membranes, and are involved in chronic degenerative diseases. Free radicals amplify inflammation by causing release of pro-inflammatory cytokines. Free radicals can be caused by many factors such as stress, disease and age. Some oxygen-derived free radicals can produce ischemia in the small bowel and stomach of cats. Combinations of antioxidants have been reported to improve serum vitamin status, suppress lipid peroxidation and distributes the effects of exercise on the immune system. The most common antioxidants found in cat gastrointestinal diets are vitamin E and vitamin C.

Vitamin E
The addition of Vitamin E as an antioxidant in gastrointestinal health cat food diets can have a positive effect of improving the animal’s immune function and prevent against infections. Vitamin E is a free radical scavenger that functions as a chain-breaking antioxidant to prevent free radical damage of cell membranes. Vitamin E aids in protecting cells from highly reactive oxygen species within the lungs, muscles, skin, brain, tissues and red blood cells. Supplementation of vitamin E in the diet benefits the immune system and improves resistance to infections and diseases.

The National Research Council (NRC) suggested a ratio of vitamin E to polyunsaturated fatty acids be 0.6:1 to ensure enough vitamin E to combat any free radicals. Polyunsaturated fatty acids (PUFA) are prone to oxidative destruction in cellular membranes and increases the requirement for antioxidants.

Vitamin C
Vitamin C (ascorbic acid) is a water-soluble antioxidant and a free radical scavenger where it will donate an electron to compounds with unpaired elections or reactive but not radical compounds. Supplements of Vitamin C reduced oxidative DNA damage in cats prone to renal insufficiency, and can be beneficial to add into diets for cats suffering from renal diseases. Vitamin C is not essential for cats as it is not required by the Association of American Feed Control Officials (AAFCO), however is commonly added into pet foods as an antioxidant. Ascorbic acid is known to not only be an antioxidant, but also to function in gene expression, as a co-substrate, and have unique biosynthetic pathways in different organisms.

Fatty Acids
A fat is a type of lipid which comes in the form of many different molecules throughout the body, and fatty acids are just one type of fat that can be found. Fatty acids come in a variety of molecular shapes, sizes and chemical compositions. They can also be divided into many different categories. Fatty acids can be can come attached to different molecules like carbohydrates or proteins and can elicit a wide range of functions in the body. Some of those functions include: providing long-term energy storage, insulation (prevents heat loss, protects vital organs, helps transmit nerve impulses faster), structure, transportation around the body for nutrients and other biological molecules, and can also be precursors to other compounds in the body such as hormones (some of which are important for gut/immune/overall health). The length, degree of saturation and configuration of a fatty acid affects how it is broken down, absorbed and utilized in the gastrointestinal tract (GIT).

Inflammation
Inflammation is the process by which the body begins to heal and defend itself from viral and bacterial infections and physical damage like burns or cuts. Typical signs of inflammation are: redness, swelling, heat, pain and loss of function in the affected area. The inflammatory response is a normal response for the body to make when injured but if the response gets out of control or becomes excessive, it can cause damage in the host with a wide range of effects from mild allergies to severe GIT diseases. Inflammation is then an important response to focus on because it is very involved in the host’s defense mechanisms and is often involved in GIT diseases. The inflammatory process begins with intracellular and intercellular communication around the body using chemical mediators like chemokines and cytokines, which left unregulated can get out of control and cause excessive inflammation. Anti-inflammatories and the ratio of omega-6 to omega-3 fatty acids can influence the initiation and severity of the inflammatory response, controlling factors like intracellular signaling cascades and receptors for inflammatory molecules. Fat (adipose tissue) is also an important and potent mediator in the inflammatory process and therefore regulation of fat stores is important in keeping the inflammatory response in the body under control.

Nutrition and GIT in Cats
To achieve optimal cellular health (especially in the gut) and to maintain a healthy microbiome, proper nutrition is necessary (nutrition is multifactorial an complex). Cats with GI diseases must consume an easily digestible diet with the appropriate nutrients provided by easily digestible ingredients and in the correct ratio which is recommended to be fed in small portions frequently throughout the day, so as o not overwhelm the digestive system. It is also important for fat to be digestible because too much undigested fat that reaches the end of the digestive tract (colon) has the possibility of being fermented and can worsen the symptoms of GIT disease and induce other reactions like diarrhea. It has also been suggested that cats should eat diets tailored to the section of the GIT that is diseases. When certain nutrients like fructooligosaccharides (FOS) are included in the diet, the microbiome and fatty acid content are often changed for the better. An example would be less branched-chain fatty acids (BCFAs; which are more difficult and take more time to digest) are produced and more short-chain fatty acids (SCFAs; which are easier to digest and are more readily available sources of energy which can be used for supporting cell turnover keeping cells, like those found in the GIT, healthier thereby improving GIT health and immune function) are produced. FOS can also impact production of other fatty acids.

Fat Digestion
Cats have a higher tolerance for a greater amount of fat in the diet, and although its digestion is complex and important (pertaining to its many functions and its influence on immune and inflammatory responses), fat composition in the diet appears to have a small effect on GI disease in cats. Taurine is an essential sulphur-containing amino acid for cats and some other mammals with many unique essential functions, one of which is the conjugation of bile acids which are important in the metabolism of fatty acids. Fat levels are important so that the animal wants to eat the diet. So, although high levels of fat may be detrimental, too low a fat level in the diet and the animal will not eat it. Low levels may be only beneficial if the GI disease involves maldigestion, malabsorption and/or influences the population of bacteria in the gut too much.

Fatty Acids and Gastrointestinal Health in Cats
One group of fatty acids that is particularly important for gastrointestinal (GI) health is the essential fatty acid (EFA) group. All EFAs are polyunsaturated (they have more than one double bond in their fatty acid chain). EFAs are important to have in the diet in adequate amounts, especially for the cat, as since they are essential (meaning the body produces little to none so it must be included in the diet) and cats have very low activity or simply lack the digestive enzymes to generate the EFAs that are important in mediating the inflammatory response. EFAs also vary in size, have many different functions and can also be further divided into other categories, two of which are very important for GI health: the omega-6 and omega-3 fatty acids (the omega in the name denotes the position of the first double bond in a fatty acid counting from the methyl end). These fatty acids are most effective when present in adequate and appropriate balanced ratios dependent upon stage of life and production of the animal. One very important function of EFAs is the production of eicosanoids (molecules that are important in immune and inflammatory regulation). Eicosanoids are like hormones and act in a local fashion with short lives. Different EFAs have different effects on the inflammatory response. Omega-6 fatty acids at high levels can suppress the functions of the immune system (large part of which is located in the GIT) and promote inflammation, platelet aggregation and hypersensitive reactions like allergies. Omega-3 fatty acids act in the opposite direction of omega-6 fatty acids by: promoting anti-inflammation and depressing aggregation and immunosuppression. Ratio of omega-6 to omega-3 fatty acids can be changed using diet, optimal ratio of omega-6 to omega-3 fatty acids is considered to be within the range of 5:1 to 10:1. The right ratio (different for everyone as everyone is unique) helps reduce inflammation and mediate immune responses as both omega fatty acids utilize the same enzymes in their metabolic journey. Some sources of omega-6 fatty acids include: corn oil, sunflower oil and soybean oil. Some sources of omega-3 fatty acids include: cold-water fish oil, flaxseed, canola oil and soybean oil.

Areas for Improvement
There is very little research on cats in general, especially when diving into very targeted topics like GIT health of cats and the effects of fatty acids of any length on their digestive system, especially cats with GIT disorders. GIT diseases are common in cats and it has been suggested that in the case of long-term GI diseases, diet is extremely important in modulation and manipulating the effects. Levels of fat included in the diet should be studied more and monitored as not only does adipose tissue play a role in the inflammatory process, but it is also used as a palatant to make food more appealing. As fat is high in energy, overeating (which can cause an animal to become overweight or obese) is not uncommon in foods with high levels of fat as fats are very palatable. Although not well studied, evidence from previous studies completed in animals and humans (who have similar digestive tracts to cats) suggest a proper ratio and use of omega-6 to omega-3 fatty acids will help mediate inflammatory diseases, especially ones present in the GIT.