Friday, June 26, 2009

Pet nutrition in Layman’s terms: Part 2 Fat

Those readers of you who have read my first comment in this series (Pet nutrition in Layman’s terms: Part 1 Nutrients and Protein) know already about the reasons for and background behind this series of comments, please scroll right down to “Fats” (sorry, blog software does not allow me to add hyperlink, or should I better say, I don’t know how to do it?).

Does the food I’m providing meet my pet’s nutritional needs? As our knowledge of the relationship between diet and health continues to advance and as the range of foods available for our pets continues to expand, it’s more important than ever to base feeding choices on good information. This information can come from various sources. For example from “Nutrient Requirements of Dogs and Cats”, a technical report issued by the National Research Council as part of its Animal Nutrition Series. The Food and Drug Administration relies on information in the report to regulate and ensure the safety of pet foods (Or better: is supposed to ensure, as we all know too well, pet food isn’t always safe). Scientists who study the nutritional needs of animals use the Animal Nutrition Series to guide future research. The series is also used by animal owners, caretakers, and veterinarians to develop specialized diets for individual animals.
To provide good information is one of my goals with this blog. At various I publish comments and articles about pet nutrition in general on this blog. The problem is that many of those articles sometimes get very technical and can be confusing to some of us, others again may be based on opinions or written for a certain purpose, like for example in order to sell a certain type or brand of food. What I have been missing is simple explanations, kind of written in Layman’s terms and understandable for everybody, easy to read and short and quickly getting to the bottom of things. That was until now when recently, while doing my daily research work, I came across a course, which I decided to publish here with slight modifications. The site itself looks to me like it has not been maintained for quite a while, the last time its copyright notice was updated was in 2005 and many parts of the site are no longer accessible or corrupted. We don’t have to worry about the age of the info, nothing has changed about the basics. The Australian pet food manufacturer Advance created the self study course in cooperation with the Waltham Centre for Pet Care and Nutrition. Waltham, since 1965 has contributed to the advancement of global knowledge on nutrition for companion animals and now has over 600 research and development personnel all over the world. They continuously study in detail the nutrition and behavior of companion animals in a non invasive environment. Their studies cover many specialist areas including veterinary medicine, dietetics, biochemistry, animal behavioral science and breeding science. While this initially all sounded too science oriented to me, it turned out they came up with a pretty cool “crash course” and I decided to share what I was able to salvage here on this blog. As a result I hope I will be able to come up with a simple series designed for those of you who want to learn more about pet nutrition. A series suitable for breeders, vet nurses, pet store retailers, animal trainers or any pet owner who simply wants to learn more about feeding their dog or cat. Today I am going to talk about another basic nutrient, which is “Fat”:

Fat is differentiated in two types: Animal fat, sourced from dairy produce, meats and fish and plant based fat, deriving from seed oils and nuts.

Fats consist largely of mixtures of triglycerides. Each triglyceride is made up of a backbone of glycerol, to which three fatty acids are attached. The differences between one fat and another are mostly the result of the different fatty acids in each. Fatty acids can be saturated i.e. contain no double bonds, or unsaturated with one or more double bonds. Polyunsaturated fatty acids contain two or more double bonds in their hydrocarbon backbone. Essential fatty acidsThere are two main families of polyunsaturated fatty acids: omega-6, and omega-3. Some fatty acids contain double bonds that cannot be made by animals, and therefore must be supplied in the diet. They are termed essential fatty acids. The longer chain polyunsaturated fatty acids can be made in the body through progressive elongation and de-saturation of these fatty acids.

For the scientifically adversed of you:
Structure of omega-3 and omega-6 fatty acids
Linoleic acid (omega-6)
(18:2n6; 18-carbon backbone, two double bonds, first at sixth carbon)

Alpha-linolenic acid (omega-3)
(18:3n3;18-carbon backbone, three double bonds, first at third carbon)

Essential fatty acid (EFA) requirements in dogs can be met by linoleic acid (omega-6). Cats, on the other hand, lack a key enzyme needed for the production of the longer chain omega-6 fatty acids from linoleic acid, and therefore need arachidonic acid in their diet as well.

The functions of fat can be defined as

  • Playing a key role in the absorption, transport and storage of the fat soluble vitamins (vitamins A, D, E and K)
  • Being an energy source (containing 2½ times more energy per gram than either proteins or carbohydrates)
  • Providing essential fatty acids, necessary for cell membranes, kidney function and reproduction
  • Increasing palatability of foods, particularly dry complete products

What happens if fat is not supplied in sufficient volume? Essential fatty acid deficiency may occur in animals eating diets low in fat or poor quality commercial dry food for long periods. On rare occasions, animals develop fatty acid deficiency in association with liver disease, biliary disease, chronic pancreatitis or mal-absorption problems. Signs of EFA deficiency in dogs and cats include dull, scurfy coat, fatty liver, anaemia and impaired fertility. Changes in the lipid film of the skin can alter the normal bacterial flora of the skin, and predispose the animal to secondary bacterial infection, a condition also known as fat deficiency seborrhea.

On the other hand, excessive fat in the diet can result in an excess calorie intake. In the long term this can lead to obesity and/or growth abnormalities in young growing animals. As animals usually eat to satisfy their energy requirements, a high fat diet may not be balanced with respect to other essential nutrients. Diets high in polyunsaturated fatty acids can become rancid through oxidation. Inadequate amounts of antioxidant in dry foods or prolonged storage of food, especially at high temperatures, may cause the fat in the food to become rancid. As fats are oxidized, the essential fatty acids are destroyed, as are vitamin D, vitamin E and biotin. In general, dry foods should be kept at room temperature, out of direct sunlight, in non-lipid-permeable or non-absorbing containers and not stored open for longer than a month.

Summarizing all this, these are the key points to remember about fat:

  • They provide a concentrated energy source
  • Dogs need the essential fatty acid, linoleic acid
  • Cats also require arachidonic acid in their diet
  • A long term EFA deficiency can cause skin lesions, poor coat condition and reproductive failure

The concentrations of saturated fatty acids, and monounsaturated fatty acids present in the diet affect the minimum dietary requirement for EFA. Based on data obtained from studies of rodents, it has been suggested that high intakes of saturated fatty acids, trans fatty acids or oleic acid, compete with the metabolism of EFA and thereby increase the body's EFA requirements. (*1, *2) Because of this dependence on the fat content of the diet, any minimum nutrient requirement for linoleic acid, or other members of the omega-6 family of fatty acids for dogs has not been precisely determined.

*1: Mead, J. F. (1980). Nutrients with special functions: Essential fatty acids. Chap.8, In Human Nutrition: A Comprehensive Treatise. Eds. R.B. Alfin-Slater and D. Kritchevsky, Vol. 3A, Plenum Press: New York.
*2: Holman, R. T. (1981). Effect of dietary trans fatty acids upon prostaglandin precursors, In Nutritional Factors: Modulating Effects on Metabolic Processes. Eds R.F. Beers and E.G. Bassett, Raven Press, New York.

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