The Cutting Edge of Dog Food Technology
Gregory Reinhart, Ph.D. and Daniel P. Carey, DVM
If you're into learning about dog food, or if you hang out at the health food store, you've probably heard about "essential fatty acids," "marine lipids," "linoleic acid," "omega-3" and "omega-6 fatty acid." You may have an idea that these are all good for the heart, but don't know why -- or exactly what a fatty acid is.
One of the hottest areas of nutritional research for dogs happens to be: fatty acids. In this article, we'll take a look at fatty acids, what they are, and how a proper balance of certain fatty acids in the diet can help solve the problems of a dog who itches, scratches and chews on himself all the time.
What Are Fatty Acids, Anyway?
Fats are made up of fatty acids. There are many different fatty acids, but they all have a common structure.
Each fatty acid is a chain of carbon atoms with oxygen atoms hooked on at one end (COOH or carboxyl group) and three hydrogen atoms hooked on at the other end (CH3 or methyl group). The end with the oxygen is called the alpha end. The end with hydrogen is the omega.
Fatty acids differ in two respects: how many carbon atoms are strung together, and where there are double bonds instead of single bonds between carbon atoms. If the first double bond is located three carbons away from the omega end, the fatty acid is considered an omega-3. If the first double bond is located 6 carbons in from the omega end, it's an omega-6 fatty acid.
Here's The Difference Between Saturated and Unsaturated Fats
Let's look at some other kinds of fats. If the fatty acid has no double bonds, it is a saturated fat. These tend to be solid at room temperature, and in people, most saturated fatty acids cause the blood cholesterol to increase.
Unsaturated fatty acids have one or more double bonds. Polyunsaturated fatty acids have three or more double bonds. The unsaturated and polyunsaturated are generally less likely to raise the cholesterol in humans. Dogs don't have to worry about cholesterol, except when they have certain diseases. The unsaturated are more liquid at room temperature, while the polyunsaturated fats are definitely liquid at room temperature.
The length of the fatty acid chain -- how many carbons are strung together -- will help determine whether a fatty acid is solid or liquid. Shorter chains tend to be more liquid.
For example, acetic acid is a short fatty acid with only two carbons. It's found in vinegar. Butter has much butyric acid, which is a four-carbon fatty acid. Much longer fatty acids, with 16 and 18 carbons, are found in beef and pork, and are relatively solid.
Fish oils are 20 to 24 carbons long. These are very long chains, yet tend to be liquid because they're highly unsaturated -- they have many double bonds.
Fish And Relatives Stink After Three Days
As the chain gets longer, or as it gets more unsaturated, it is more likely to go rancid. Remember the bacon drippings your mother saved in a can? Once they cooled, they turned relatively firm, and could sit out for months. They were solid at room temperature, and didn't go rancid because they were highly saturated.
On the other hand, there is an old saying that "Fish and relatives stink after three days." That's because fish oil is highly polyunsaturated and goes rancid quickly unless a preservative is used. In fact, all fatty acids in the dog's food need to be protected from going rancid. Rancid fats can make dogs very sick. Preservatives, such as vitamin E, BHA, BHT and ethoxyquin, work to protect the fatty acids. (There is no preservative for relatives.)
There's No Mystery To Marine Lipids
At the beginning of this article, we mentioned "marine lipids." Lipid is another term for fat. Many of the marine lipids, which are mostly from deep-sea fish, have a structure different from the oils from freshwater fish. They have more omega-3s in their fatty acids. The key is that these fish eat lots of plankton and other plants that produce the omega-3s. Their bodies concentrate the omega-3s.
Land mammals just don't have much of the omega-3s in their fat, unless they're eating a diet which includes omega-3s, such as flax or soybeans. If you eat fish, you get a really good supply of omega-3s in the diet.
Your Dog Needs Linoleic Acid!
There is only one fatty acid that dogs really need, and it's an omega-6: linoleic acid. Dogs can't make their own, so it must be in the diet.
For the dog, linoleic acid is an essential fatty acid, as it must be included in the fat content of the diet. If the dog's diet is deficient in linoleic acid, the result will be a scruffy, dry coat. In some cases the coat might also feel oily. In addition, the coat, paw pads and nose leather may not be healthy. Other problems occur, but they are unseen, inside the cells.
Luckily, the amount of linoleic acid needed to prevent a deficiency is small, Good sources include beef, pork, chicken, and oils from corn, safflower and soybean.
Various studies have shown that adding sources of linoleic acid to the diet cures the symptoms of deficiency. The deficiency in linoleic acid is also seen in the disease known as Generic Dog Food disease. As you can guess, some dogs fed generic dog food from the supermarket were found to have a linoleic acid deficiency.
Linoleic acid is particularly important because it is required in the membrane of the cells. It helps to maintain a state where the electrolytes (minerals and fluids) can get back and forth across the membrane. It helps prevent the moisture loss from cells which causes flaky, dry coats.
Are Other Fatty Acids Needed?
What about other fatty acids? Deficiencies are not a problem, as the dog appears to make all of the other fatty acids he needs.
Questions have been raised, though, debating whether alpha-linolenic acid (ALA) is needed in the dog's diet. This is due to some reproductive problems seen in rat studies. While different studies have shown contradictory results, and the rat is not a good model for dogs, the question is still there. More research is needed into ALA requirements for dogs. ALA, by the way, is an omega-3.
New Research Looks Inside Cells
The really exciting research in fatty acids is now unlocking what's happening inside the dog, in the cells.
The unique thing about the omega-3s in the diet is that you are what you eat. The fatty acids in the diet show up in the body fat.
The ability of the diet to influence body fat composition is well known in poultry, pigs and people. It works in dogs, too.
If you add omega-3 fatty acids to the diet, it shows up in the fat and the cell membranes. How quickly? That's a function of how much is circulating in the bloodstream, and how fast the cells are being remodeled.
Some cells, which are quicker, pick up the omega-3 fatty acids faster. Intestinal cells, for example, take about two weeks from feeding before omega-3s show up. It's thought that skin cells take 6 to 8 weeks.
This becomes important because of the impact omega-3s and omega-6s have on inflammation. Omega-6 fatty acids (such as linoleic acid) tend to promote inflammation, while omega-3s are less inflammatory.
Inflammation -- What's Really Going On?
Let's take a look at what goes on when skin gets inflamed. Inflammation is a cell's response to some kind of insult, either physical or chemical. The insult could be a scrape or a reaction to something like a mosquito bite or flea bite.
Inflammation is simply the cell's defense mechanism. One of the cell's reactions is to produce compounds that attempt to protect it and some of its neighbors. Those compounds are made from fatty acids and are called eicosanoids. The eicosanoids that are made from omega-6s attract many white blood cells to the site, and produce much of the pain and itching associated with the mosquito bite. Platelets collect in an attempt to stop bleeding. The omega-6s are very pro-aggregatory -- they cause the coagulation or sticking together of the platelets.
The visible signs of inflammation are redness, swelling, heat, and pain, all in varying degrees. We've all had those symptoms from our different bites and scrapes.
If you've ever wondered why an injury feels hot, here's your answer: Some of the heat difference is due to the eicosanoids causing the blood vessels to dilate, which lets plenty of blood come pumping through. All that blood brings warmth to the site.
Some inflammation is good, and a natural response. But sometimes the body can get out of hand with its reactions. In the case of hot spots, the inflammation causes the dog to lick and scratch, which causes more inflammation. This self-perpetuates into a vicious cycle of more self-trauma and inflammation.
Allergies are another situation where the immune system goofs up. The immune system senses an invader when it shouldn't and starts the inflammatory process going. In actuality, there's no reason why the body should react to pollen or ingredients in the dog's food. Eicosanoids are, in part, responsible for the allergic reaction.
While the omega-6s produce eicosanoids that encourage inflammation, the omega-3s produce eicosanoids that cause much less inflammation.
Some of the eicosanoids from the omega-3s are just less potent than those from the omega-6s. But some are also anti-aggregatory.
That means they'd prefer that the platelets in the blood not stick together. This is fine, as long as you don't go overboard with the omega-3s. People in Greenland, who have a diet heavy in omega-3s from deep-sea fish and marine mammals, also bleed longer than people elsewhere. That's because the omega-3s don't help the platelets coagulate.
What It All Means
The bottom line is that if there are more omega-3 fatty acids in the cells than omega-6s, there may be fewer symptoms of inflammation such as pain and itching.
By influencing the ratio of omega-3 to omega-6 fatty acids in the cell membrane, a blend of eicosanoids will be produced, with a reduction in the symptoms of inflammation. This ratio can be changed by changing the dog's diet, since as we said before, when it comes to omega-3s and omega-6s, you are what you eat.
Some inflammation is necessary because it's a defensive mechanism, so you don't want to eliminate the omega-6s. Anyway, the omega-6 linoleic acid is necessary to maintain moisture in skin cells. But if we put the right proportion of omega-6s to omega-3s in the diet, it will end up properly proportioned in the cell membranes. That means we can increase the amount of eicosanoids that help reduce inflammation.
Omega-3 fatty acids may also influence the way the coat looks. But overall, they have more of a role in controlling inflammation, not preventing it.
By modifying the body's response, we can help relieve the itching of a dog with allergies. By helping the skin react in a more controlled fashion, we can avoid hot spots and hair loss from allergy-caused licking. We may even be able to reduce the allergy problems of dogs who are troubled by flea bites, although this has not yet been demonstrated scientifically.
Influencing The Ratio of Omega-6 to Omega-3
Now you know that you need to keep track of the ratio of omega-3 to omega-6 fatty acids in your dog's body. You know you can do it through the diet. But what should the ratio be? How can you affect it?
Research indicates that the ideal ratio of omega-6 to omega-3 fatty acids in the diet is between 5 to 1 and 10 to 1. This allows the body to have all of the omega-6 linoleic acid it needs to keep the skin cells healthy, while still helping to reduce inflammation. These ratios are similar to the ideal ratios for rats and people.
There are two ways to get the proper ratio into your dog: in the dog food, or by adding omega-3 supplements.
The problem with supplements is that there is no easy way to tell how much of the omega-6s are in your dog's present diet. If you don't know how much omega-6 fatty acids your dog is getting, there's no way to figure out how much of the omega-3s is needed to bring the ratio back into line. Remember, you don't want to get too much of the omega-3s or your dog will have a slower blood-clotting time.
Too few omega-3s won't show up as a problem, but it also won't make any difference to your itchy dog. That's because the mass of eicosanoids from the omega-6s will overwhelm the few eicosanoids from omega-3, resulting in continued itching and inflammation.
Supplements are fairly expensive, costing between 20¢ and 60¢ a capsule at the veterinarian. In addition, current studies show that the supplements give good results only about 25% of the time.
If your dog has fleas, that can affect the impact of omega-3 supplements, too. Many veterinarians will suggest you try the supplements, and there will be some successes and some failures. While it hasn't been researched, the possible reason for the poor success rate might be that the dogs were on a high omega-6 diet, and the amount of the omega-3s in the supplement just wasn't enough to make a difference.
Finding a Food With A Good Ratio
Since supplementation isn't a good option, the only other choice is to feed a diet where the omega-6 to omega-3 ratio is predetermined by the manufacturer. This is difficult, since most manufacturers haven't caught on to the need to monitor the ratio.
In addition, the test to determine the ratio is not an easy one, and most pet food companies and independent test labs don't have the equipment to do it. (Very few companies that make food for people have the equipment either, even though fatty acid research is hot on the people side, too.)
For now, you can make some educated guesses based on ingredients. If the diet has safflower oil or corn oil in it, it's likely to be high in the omega-6 linoleic acid. There should be fish oil or fish meal to provide balancing omega-3s. In fact, seeing fish oil, fish meal or flax in the ingredients is the best clue you have in finding a diet that might have a good balance of fatty acids.
Dog foods on the market vary widely from the optimal ratio of between 5 to 1 and 10 to 1. Before it was reformulated, one major brand had a ratio of 16 to 1. Safflower oil was added to boost the linoleic acid content. That altered the ratio of omega-6 to omega-3s to a whopping 50 to 1. It would take somewhere between two and six times the recommended dosage of omega-3 supplements to bring a dog fed that food back into line.
Beware of foods that promise they are high in linoleic acid. Unless it's balanced with the omega-3 fatty acids, it may cause more itching than other foods.
Remember that it takes several weeks after a change in the diet before the omega-3s are taken up by the skin cells, so don't expect immediate relief. If your dog is in so much trouble that he is destroying his skin, take a quick trip to your vet. A dose of steroids quickly interrupts the inflammatory process, stopping the self-trauma right away. You'll still see a difference in skin itching later on, when the effect of the steroids wears off.
For many dogs, none of this really matters. They don't develop allergies, flea problems or hot spots. But if your dog is one who has recurrent problems, it would pay you to search for a different food.
The future of dog food is clear: as the data become more readily available, more companies will start adjusting the fatty acid ratio in the diet. More will jump on the bandwagon.
Greg Reinhart is Director of Strategic Research and has done most of the fatty acid research for The Iams Company. He is also involved in several studies investigating exercise-induced physiological changes in Alaskan sled dogs. Dan Carey is Director of Technical Communications for Iams.