Fat Overview - Nutrition

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What is Fat?

Fat is a macronutrient that is comprised of straight chain hydrocarbons found as either glycerol (e.g. triglycerides and phospholipids) or non-glycerol substances (e.g. waxes and cholesterol). Glycerol is a chain of three hydroxylated carbons that form the backbone of lipid structures. Dietary fats are predominantly found as the glycerol molecule triglyceride. Fat storage within the body is referred to as adipose tissue and the terms “fatty acid” and “lipid” are used interchangeably with the term fat.

Fats can be found as solids or liquids at room temperature depending on the degree of saturation and unsaturation present. Saturated fats are those with single bonds between each carbon atom causing the molecules to pack together in a linear fashion preventing fluidity. If a single double bond is present the fat is referred to as a monounsaturated fatty acid; if multiple double bonds are present it is referred to as a polyunsaturated fatty acid. Most naturally occurring double bonds are in the cis configuration imparting a kink in the molecule and preventing orderly array of fats resulting in a pliable fat or liquid oil. Processing of unsaturated fats, such as partial-hydrogenation used in preparation of foodstuffs for people, can result in formation of trans fatty acids, which chemically align like saturated fats. Partial-hydrogenation of fats and fatty acids is not used in pet food production.

Why is it Important?

Dietary fat is a rich and important source of energy for companion animals, providing more than twice as much energy per gram than protein and carbohydrate. Dietary fat is a source of the omega 6 and omega 3 essential fatty acids;[1] dietary fat is a carrier for the fat soluble vitamins A, D, E and K; and dietary fats are used to enhance and improve the palatability of pet foods. Fat and fatty acid oxidation is also the preferred energy substrate during endurance activities (such as racing sled dogs).[2],[3]

Roles in the Body

EPA and AA compete for COX and LOX enzymes

Fat is an important substrate for the production of energy; in dogs it is the preferred energy substrate during endurance activities.[2],[3]

  1. Skin and Hair Coat: Epidermal keratinocytes produce linoleic (LA) enriched ceramide to form the water permeable barrier of skin.[4] Dogs fed higher fat diets in general experience improvement in coat quality irrespective of essential fatty acid concentration (above minimal requirement).[5]
  2. Inflammatory Mediators: Arachidonic acid (AA) and eicosapentaenoic acid (EPA) are concentrated in cellular membranes and are used as precursors for inflammatory mediators and cell signaling pathways.[1] Both AA and EPA can be used by cyclooxygenase (COX) or lipoxygenase (LOX) to form the eicosanoids: prostaglandins, prostocyclins, thromboxanes, and leukotrienes. Eicosanoids formed from EPA are less pro-inflammatory than those produced from AA.
  3. Brain and Retinal Development: Docosapentaenoic acid (DPA) is synthesized in the liver from EPA and is transported to the retina and other nervous tissues where it is converted to docosahexaenoic acid (DHA). During growth, synthesis of these long-chain omega-3 FAs is inadequate to support normal retinal and brain development and a dietary source of EPA or DHA is considered conditionally essential.[6]

Consequences of Fat Deficiency

Low fat foods are poorly palatable to both dogs and cats. Fat provides more than twice the energy content of protein or carbohydrates, and low fat foods may not provide sufficient daily energy intake to support growth of puppies and kittens or weight maintenance in adults. Depending on the specific essential fatty acid lacking in the diet, clinical signs can range from poor skin and hair coat (LA in dogs and cats),[7],[8],[9] inability to maintain a successful pregnancy (AA in queens)[10], and potentially inadequate absorption of fat-soluble vitamins.

Toxicity

Dogs and cats in general are able to tolerate a wide range of fat intake with tolerable upper limits of 70% of the calories consumed[1], but in dogs, abrupt and dramatic increases in fat intake can result in self-limiting diarrhoea/steatorrhoea to life-threatening pancreatitis[11] especially in breed with underlying dyslipidemias such as Miniature Schnauzers and Yorkshire Terriers.[12],[13] High fat contents also increase energy density and overconsumption of energy dense foods may be a risk factor for the development of obesity in dogs and cats if portion control is not practiced. Increased dietary fat also increases the requirement for vitamin E as an antioxidant. Consuming a high fat diet with inadequate vitamin E intake can result in oxidative damage within the body, especially the retina and lens.[14],[15]

Dogs and cats with a history of pancreatitis, gastrointestinal disease (especially lymphangiectasia), or dyslipidemias are less tolerate of dietary fat and total fat intake often requires restriction to help manage clinical signs of disease or prevent exacerbation of underlying medical condition.

Dietary Sources

Animal fats (associated with muscle meat, organ meat, and eggs) are good sources of dietary fats for dogs and cats, though the EFA content will vary the source diet of the individual food animals. Other dietary sources of fat and EFA include seed oil (e.g. corn, sunflower, linseed) or fleshy fruits (such as olive or palm). Animal-based fats are more palatable for dogs and cats than plant-based fats.[1] Coconut oil contains medium-chain triglycerides (MCTs) and provides a source of moderately palatable fat for dogs but is deficient in EFA; increased concentrations of MCTs in the diet will also adversely affect palatability of the diet for dogs[16]. Cats will avoid eating diets with MCT included and coconut oil should not be fed to cats.[17]

Diets with higher fat contents also require a large concentration of dietary antioxidants to prevent rancidity (fat oxidation) during processing and storage.

Diagnosing Fat Deficiency

The clinical signs of fat deficiency are related to deficiency of omega 6 or omega 3 fatty acids and/or the fat soluble vitamins A, D, E or K.

References

  1. 1.0 1.1 1.2 1.3 National Research Council (NRC). (2006) Fat and Fatty Acids. In Nutrient Requirements for Dogs and Cats. Washington, DC: National Academies Press p.90-104.
  2. 2.0 2.1 Downey RL, et al. (1980) Diet of beagle affects stamina. JAAHA;16:273-277.
  3. 3.0 3.1 Hill RC. (1998) The nutritional requirements of exercising dogs. J Nutr;128:2686S-2690S.
  4. Elias PM, et al. (1980) The permeability barrier in essential fatty acid deficiency: Evidence for a direct role of linoleic acid in barrier function. J Invest Dermatol; 74:230-233.
  5. Conner WE, et al. (1992) Essential fatty acids: The importance of n-3 fatty acids in the retina and brain. Nutr Rev ;50:2129.
  6. Kirby NA, et al. (2009) Skin surface lipids and skin and hair coat condition in dogs fed increased total fat diets containing polyunsaturated fatty acids. JAPAN (Ber);93:505-511.
  7. Hensen AE, et al. (1948)' Susceptibility to infection manifested by dog on low fat diet. Fed Proc ;7:289.
  8. Hensen AE, et al. (1954) Sequence of histological change in skin of dogs in relation to dietary fat. J Nutr ;52:541-554.
  9. Codner EC and Thatcher CD. (1990) The role of nutrition in the management of dermatoses. Semin Vet Med Surg (Sm Anim);5:167-177.
  10. MacDonald ML, et al. (1984) Effects of linoleate and arachidonate deficiency on reproduction and spermatogenesis in the cat. J Nutr ;114:719-726.
  11. Lem KY, et al. (2008) Associations between dietary factors and pancreatitis in dogs. JAVMA ;233:1425-1431.
  12. Xenoulis PG, et al. (2011) Serum triglyceride concentrations in Miniature Schnauzers with and without a history of probable pancreatitis. JVIM ;25:20-25.
  13. Hess RS, et al. (1999) Evaluation of risk factors for fatal acute pancreatitis in dogs. JAVMA ;214:46-51.
  14. Davidson MG, et al. (1998) Retinal degeneration associated with vitamin E deficiency in hunting dogs. JAVMA;213:645-651.
  15. Hayes RC, et al. (1970) Vitamin E deficiency and fat stress in the dog. J Nutr ;99:196-209.
  16. Remillard RL and Thacher CD. (1989) Dietary and nutritional management of gastrointestinal diseases. Vet Clin No Am Sm Anim Prac ;19:797-817.
  17. MacDonald ML, et al. (1985) Aversion of cat to dietary medium-chain triglycerides and capryic acid. Physiol Behav ;35:371-375.



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