You may have heard about them in the last few years, but do you know that antioxidants also have an important place in your dog’s or cat’s diet? By understanding what they are and their impact on your pet’s health, you will be able to choose the right food for your pet and ensure they live the best life possible.
Antioxidants are molecules that inhibit the oxidation of other molecules, providing a broad spectrum of protective responses that organisms can use to counteract free radicals. Antioxidants bind to free radicals by donating one of their own electrons, stopping the reaction of that free radical and thereby potentially reducing damage to cells of the body. When donating electrons, antioxidants do not become free radicals themselves, since they are stable in all forms. They will simply remain out of service until they are recharged. It is estimated that each body cell endures 10,000 oxidative hits every day from errant free radicals, making antioxidants important for warding off cell damage by “cleaning up” or removing free radicals before they can do harm. Given the ubiquity of free radicals, the body can rely on two types of antioxidant systems within the body. The first is a set of antioxidant enzymes. For instance, some specific enzymes convert free radicals into harmless water or oxygen. Other enzymes degrade oxidized proteins and fats, or clip out and replace damaged pieces of DNA. The second type of antioxidants are introduced to the body through diet. Vitamins, for example, act to buttress the cell’s protective enzymes. Vitamins that act as antioxidants include vitamin A, vitamin C, vitamin E and the mineral selenium. Other non-vitamin substances that act as antioxidants include lutein, lycopene, carotenoids and polyphenols. For instance, carotenoids can act as chemical quenchers of free radicals via electron transfer following structural modification.
A dog’s or cat’s body naturally gets rusty during normal life (natural degradation, environmental factors) just like metal. Free radicals act like the rusting process. Antioxidants act like rustproofing.
Free radicals are formed during normal bodily functions, such as when cells burn food for energy or even when the body is fighting off bacteria or viruses. In these normal occurrences, free radicals do not have a detrimental impact. However, our pets can be exposed to certain external factors that can trigger the production of free radicals. Pollution, environmental stress, excessive light exposure, manufactured chemicals, eating an unhealthy diet, unbalanced exercise, certain medications and/or treatments (to name a few) create a surplus of free radicals in their body. This imbalance between the production of free radicals and the ability of the body to counteract or detoxify their harmful effects through neutralization by antioxidants defines oxidative stress. Aging and age-related diseases (osteoarthritis, neurodegeneration, cancer, cardiovascular diseases) reflect the inability of the animal’s antioxidant defenses to cope with oxidative stress over time. Free radicals are most often implicated in disease development and cell damage that leads to aging, whereas antioxidants are intimately involved in the prevention of these.
When an apple is cut open, an enzyme (polyphenol oxidase) is released from the cells of the apple and reacts with the oxygen in the air. This is what causes the fruit to turn brown, a reaction similar to rust forming on metal. Lemon juice is able to prevent this reaction from taking place because it contains ascorbic acid (vitamin C). The ascorbic acid reacts first with the oxygen, preventing the polyphenol oxidase from doing so. As a result, the apple doesn’t turn brown!
Companion animals, such as dogs and cats, have built-in defenses to reduce the impact of free radicals; however, dietary antioxidants are also beneficial. Specifically, a number of plants contain naturally occurring compounds that act as antioxidants, including flavonoids and polyphenols. Various fruits and vegetables have been analyzed by scientists to measure their antioxidant power or their oxygen radical absorbance capacity (ORAC). Higher ORAC values imply a higher measured antioxidant activity. For instance, with their high content of phytochemicals such as flavonoids, berries and berry products are excellent antioxidant sources that can improve memory in dogs.1 Carotenoids (red, yellow and orange pigments found in plant foods such as carrots and tomatoes) also pack a powerful antioxidant punch. It has been shown that dietary beta-carotene stimulates natural immune responses in dogs.2
Without antioxidants, the fat in pet food will become rancid in a very short time. Cats and dogs don’t like rancid food; it smells bad and tastes even worse. It can also cause dangerous health problems.
Rancid fats are fats that have been exposed to oxygen and have gone through a process of oxidization. Rancid fats lose nutritional value, breakdown vitamins and antioxidants and are the perfect breeding ground for bacteria. A food that contains rancid fats can actually become toxic, causing diarrhea, liver and heart problems, cell damage, cancer, arthritis and even death.
The oxidative stability of fats is affected by several factors. Light, temperature, presence of transition metals and the oxygen in the air, as well as fatty acid composition, can increase the rate of lipid oxidation. For example, fats become more sensitive to oxidation as the level of unsaturation and length of the fatty acid chain increases. This means oils like vegetable and fish oil that are more unsaturated are more sensitive to rancidity.
In order to extend the shelf life of pet food and ingredients, it is useful to add antioxidants to susceptible materials. Antioxidants are classified as feed additives and defined as substances that delay the oxidative degradation processes of feedstuffs and thus improve oxidative stability. Chemical antioxidants in pet food primarily include antioxidants like ethoxyquin, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). Natural preservatives, such as vitamin E (commonly known as “mixed tocopherols”) and vitamin C (or “ascorbic acid”) are used in better quality foods. Plant extracts such as rosemary extract, which is the oily residue derived from the leaves of the rosemary plant, help prevent the oxidation of fats and protect flavors. Also, fruits like blueberry, cranberry, apple, blackberry and pomegranate have natural antioxidant effects. Moreover, chelating agents such as citric or phosphoric acid are added to bind positively charged ions of transition metals and thus delay the spoilage process.
Once oxygen and light reach the kibble, the chemical process of oxidation starts. This series of chemical reactions will diminish the vitamin content and eventually turn oils and fats rancid.