Functional ingredients for immune health

The immune system is designed to combat foreign invaders, including allergens and bacterial and viral pathogens, and its ability to distinguish foreign particles from normal body tissues is impressive. Nutrition plays an important role in maintaining the immune system. Immune health can be improved with gastroprotective, anti-inflammatory and antioxidative agents, so pet food brands may want to consider the inclusion of nutritionally active ingredients in their formulations.

The immune response

Many types of immune cells are produced in the body’s lymphoid tissues, and their ability to specialize helps them respond to the various invaders they may encounter. The immune response involves isolating the invader and neutralizing it with cytokines, a type of inflammatory mediator. During this process, free radicals are generated, causing damage to the surrounding tissues. Some nutritional components can reduce invasion, address invaders that get past initial defenses, and minimize associated tissue damage.

Ingredients benefiting the gastrointestinal tract

Since the body actively takes in large amounts of foreign substances (i.e., food) through the mouth and into the gut, it is not surprising that 70% of lymphoid tissue is associated with the gastrointestinal tract. Gut-associated lymphoid tissue (GALT) trains the immune system to recognize potential invaders, with the lining of the intestinal tract acting as a physical barrier.

Dietary fibers such as beet pulp, citrus pomace, gum arabic and tomato pomace play an important role as substrates for bacterial fermentation in the gut. These bacteria secrete short-chain fatty acids, which feed the cells lining the intestine. Prebiotics such as fructooligosaccharides, galactooligosaccharides and inulin are not only fermentable, but they also help reduce the presence of pathogens by enabling the growth of beneficial bacteria. Probiotics and postbiotics such as yeast extract and tyndallized bacteria have also been shown to favorably impact gut immune function.

Inflammation and the effects of omega-3 fatty acids

The immune system is intertwined with the inflammatory process. Invaders can cause inflammation, as does the immune response against the invaders due to the production of cytokines. Inflammation risk also increases with age, and it is associated with diseases such as osteoarthritis, obesity and diabetes.

Many pet diets incorporate omega-3 fatty acids such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Omega-3 fatty acids serve as precursors of less inflammatory lipid mediators (in contrast to those associated with omega-6 fatty acids), thus reducing inflammation. Sources of DHA and EPA include fish oils and algal oils. Some terrestrial plant oils such as flax, camelina and canola can produce an omega-3 fatty acid, alpha-linolenic acid (ALA), that can be converted into DHA and EPA in dogs. Given concerns regarding the sustainability of fish farming, algal oils have risen in popularity.

Sources of dietary antioxidants

Inflammation causes cell destruction and, consequently, the release of free radicals. Free radicals pose a danger to other cells due to their ability to damage DNA and other cellular components. To counter this, the body actively produces its own antioxidants such as superoxide dismutase and glutathione peroxidase.

The body’s antioxidant status can be further augmented by dietary sources of antioxidants. For example, vitamin E is an antioxidant added to pet food to meet nutritional requirements, and several studies have even shown added benefits from increasing the amount of vitamin E above the nutritional requirement. Also, because of its notoriety in humans, vitamin C (ascorbic acid) is often added to pet foods; however, there is limited efficacy data available on this vitamin in dogs and cats. Research into combatting COVID-19 has brought attention to the anti-viral effects of vitamins C and D.

Beta-carotene, astaxanthin and alpha-lipoic acid are additional antioxidants that have been shown to be effective in dogs and cats. Other antioxidant-rich ingredients include quercetin, Aronia berries (source of anthocyanins, quercetin, catechins and caffeic acid) and melon juice concentrate (source of superoxide dismutase), as well as other fruits and vegetables. Certain berries like cranberries contain antioxidative compounds that are believed to help in specific areas of the body such as the urinary tract. Antioxidant concentrates are often necessary to achieve efficacy.

Applications to pet food formulations

In summary, immune health can be improved with the addition of protective agents (i.e., gut actives), the management of inflammation, immunomodulators and antioxidants. Given the range of ways to improve immune health, pet food brands can differentiate themselves by using a wide array of nutritionally active ingredients while improving pet health.