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.

Structure
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)
CH3-CH2-CH2-CH2-CH2-CH = CH-CH2-CH = CH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH

Alpha-linolenic acid (omega-3)
(18:3n3;18-carbon backbone, three double bonds, first at third carbon)
CH3-CH2-CH = CH-CH2-CH = CH-CH2-CH = CH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH

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.

Canine nutrition: Energy for Dogs

Energy for Dogs is required for practically all life processes, for the action of the heart, maintenance of blood pressure, muscle repair, growth, normal body maintenance, transmission of nerve impulses, ion transport across membranes, protein and fat synthesis and the production of power. A deficiency in energy is normally seen as stunted growth, body fat reserve losses and a lower production of power and speed. Sometimes energy deficiencies go undetected and not corrected for extended periods of time and not until loss of condition, making visual identification easier, does correction take place. It is common knowledge that dog diets must contain protein, fat & carbohydrates. Although each of them have specific functions in maintaining a normal body, all of them can be used as energy.

Fat for dogs
Fats are concentrated forms of energy. Compared to protein and carbohydrates, fats contain approximately two and a half times the amount of energy per pound, so adding a little bit of fat adds a lot of calories. It is also the delivery vehicle for omega fatty acids important to healthy skin and coat.

Fat also supplies the essential fatty acids required by dogs for maintaining healthy skin and hair coat and serves as a carrier for fat soluble vitamins. Linoleic acid is one of the fatty acids dogs can get from vegetable oils or animal fat , is considered essential because it cannot be made in the body and is required to be supplied by the diet.

Although fatty acid deficiencies are rare, animals fed diets too low in fat may eventually develop deficiency symptoms including dry, coarse hair and flaky, dry and thickened skin.

In animals fed diets containing more fat than is needed, extra fat is generally stored in the body. If enough fat is accumulated over time, animals will become obese. Animals carrying excessive amounts of weight may be at greater risk for other complications. While fat is not a bad thing for your dog to eat, you should watch your dog’s fat intake.

Carbohydrates for dogs
Carbohydrates are sugars, starches and dietary fiber. The primary function of most carbohydrates is to provide energy, while fiber has a number of other functions.

Simple sugars are the smallest sugar molecules and are easily digested and absorbed. By contrast, starches or complex carbohydrates are combinations of simple sugars formed into long chains that have to be broken down by additional digestion before they can be used.

Basically, the carbohydrates in dog food are supplied by cereal grains which are broken down into simple sugars. While there aren’t specific minimum requirements for carbohydrates for dogs, they are useful as a ready source of energy.

When animals consume diets containing more carbohydrates than are needed, the excess energy is stored in the form of glycogen in the liver and muscles and is converted to fat. During periods of fasting, stress, or exercise, glycogen is broken down to glucose and delivered to the bloodstream to provide needed energy.

Carbohydrates that are not completely digested cause or are associated with persistent gastrointestinal upset, including gas and/or diarrhea. The most common carbohydrate malabsorption problem is an inability to break down lactose, the sugar found in milk

Notes:
Contributed by Canine Caviar

Pet Nutrition: Requirements and related diseases Part 2 Protein, Fats, Carbohydrates & Fiber

Purpose of this series is to explore the required specific dietary nutrient concentrations of cats and dogs based on their life stage. While the American Feed Control Officials (AAFCO) and the National Research Council (NRC) cooperate to publish dog and cat nutrient profiles for growth, maintenance, and reproduction, within these publications is little background to be found about the actual nutrients. And even less about the problems caused by malnutrition or imbalanced diets. To be more specific, in developed countries, nutritional diseases are rarely seen in dogs and cats, but only if and especially when they are fed good quality commercial rations or nutritionally balanced homemade diets. Dog or cat foods or homemade diets derived from a single food item are inadequate. For example, feeding predominately meat or even an exclusive hamburger and rice diet to dogs can induce calcium deficiency and secondary hypoparathyroidism. Feeding raw, freshwater fish to cats can induce a thiamine deficiency. Feeding liver can induce a vitamin A toxicity in both dogs and cats. Malnutrition has been seen in dogs and cats fed “natural,” “organic,” or “vegetarian” diets produced by owners with good intentions, and most published recipes have been only crudely balanced by using calculated nutrient averages. Because the palatability, digestibility, and safety of these recipes have not been adequately or scientifically tested, it is difficult to characterize all of these homemade diets. Generally, most formulations contain excessive protein and phosphorus and are deficient in calcium, vitamin E, and micro minerals such as copper, zinc, and potassium. Also, the energy density of these diets may be unbalanced relative to the other nutrients. Commonly used meat and carbohydrate ingredients contain more phosphorus than calcium. Homemade feline diets that are not actually deficient in fat or energy usually contain a vegetable oil that cats do not find palatable; therefore, less food is eaten causing a calorie deficiency. Rarely are homemade diets balanced for micro minerals or vitamins.
In part 1 of the series we talked about water and energy, today we are going to take a closer look at protein, fats, carbohydrates and fiber.
Protein is required to increase and renew the nitrogenous components of the body. A primary function of dietary protein is as a source of essential amino acids and nitrogen for the synthesis of nonessential amino acids. Amino acids supply both nitrogen for the synthesis of all other nitrogenous compounds and a variable amount of energy when catabolized. The amount of protein required depends on the age of the animal and protein quality and is different for dogs and cats.
Healthy adult dogs need around 2 g of protein of high biologic value per kg body wt/day. The cat has a higher protein requirement than most species, and healthy adult cats need about 4 g of protein of high biologic value per kg body wt/day. The biologic value of a protein is related to the number and types of essential amino acids it contains and to its digestibility and metabolizability. The higher the biologic value of a protein, the less protein needed in the diet to supply the essential amino acid requirements. Egg has been given the highest biologic value, and organ and skeletal meats have a higher biologic value than do vegetable proteins.
The dietary requirement for protein is satisfied when the dog’s metabolic need for amino acids and nitrogen is satisfied. Optimal diets should contain 22 to 25% protein as dry matter for growing puppies, and 10 to 14% for adult dogs. Optimal diets should contain at least 24 to 28% ME as protein for growing kittens, and around 20% for adult cats. Growing kittens are more sensitive to the quality of dietary protein and amino acid balance than are adults. Protein suitable for cats must supply >500 mg of taurine/kg diet dry matter. Unless synthetic essential amino acids are added, some animal protein is necessary in the diet to prevent taurine depletion and development of feline central retinal degeneration or dilated cardiomyopathy.

Without sufficient energy from dietary fat or carbohydrate, dietary protein ordinarily used for growth or maintenance of body functions is less efficiently converted to energy. Too little high biologic protein in the diet, relative to the energy density, can cause an apparent protein deficiency.
Protein requirements of animals vary with age, activity level, temperament, life stage, and health status. Most commercial dog foods contain a combination of cereal and meat proteins, with protein digestibilities of 75 to 90%. Digestibility is less for protein ingredients of poor biologic value and for poor-quality diets. If excessive heat is used in processing, proteins can become chemically unavailable for digestion and absorption. The signs produced by protein deficiency or an improper protein to calorie ratio may include any or all of the following: weight loss, skeletal muscle atrophy (dogs), dull unkempt coat, anorexia, reproductive problems, persistent unresponsive parasitism or low-grade microbial infection, impaired protection via vaccination, rapid weight loss after injury or during disease, and failure to respond properly to treatment of injury or disease. High protein intakes per se do not cause skeletal abnormalities in dogs (including osteochondrosis in large breeds) or renal insufficiency later in life in cats.

Fats: Dietary fat consists mainly of triglyceride with varying amounts of sterols and phospholipids. Fat is a concentrated source of energy, yielding ~2.25 times the ME (as an equal dry-weight portion) of soluble carbohydrate or protein. As much as 60% of the calories in a cat’s diet may come from fat, and diets that contain 8-40% fat (dry-matter basis) have also been fed successfully. Triglycerides are divided into short, medium, and long chain based on the number of carbon atoms in the fatty acid chain. Fatty acids are either saturated, indicating there are no double bonds, or unsaturated, indicating there are one or more double bonds. Dietary fatty acid profiles are reflected in the fatty acid composition of tissues and cell membranes. In general, as the fat content of a diet increases, so does the caloric density and palatability, which promotes excess consumption that results in obesity. Dietary fat also facilitates the absorption, storage, and transport of fat-soluble vitamins such as vitamins A, D, E, and K. They are also a source of essential fatty acids (EFA), which maintain functional integrity of cell membranes and are precursors of prostaglandins and leukotrienes. Animal fats are the most digestible component of the diet, and dogs can tolerate quite high dietary concentrations. However, the addition of too much dietary fat may result in excessive energy intake and subsequent suboptimal intakes of protein, minerals, and vitamins.
Dietary fats, especially the unsaturated variety, require a protective (natural or synthetic preservatives) antioxidation system. If antioxidant protection from a natural preservative system (eg, vitamin C or mixed tocopherols) or from synthetic preservatives (eg, BHA, BHT, ethoxyquin) in the diet is insufficient, dietary and body polyunsaturated fats become oxidized and lead to steatitis. Canine diets typically contain 5-15% fat (dry-matter basis) for adults. Puppy diets usually contain 8-20% fat (dry-matter basis). One reason for the wide range of fat content seen in commercial dog foods is the purpose of the diet—work, stress, growth, and lactation require higher levels than maintenance. However, because fat can add considerably more calories to a finished diet, it is important to remember that the amount of protein relative to energy must be balanced appropriately to the life stage and typical intakes expected for an animal’s size and needs.
Cats cannot readily convert linoleic acid to arachidonic acid, which must be obtained from animal sources. Recommendations include both linoleic acid and arachidonic acid at ~5 g and 0.2 g/kg diet, respectively.
Dogs have a dietary requirement for linoleic acid, an unsaturated EFA that is found in appreciable amounts in corn and soy oil. Recent studies suggest that α-linolenic acid (ALA, an omega-3 fatty acid) is also essential in dogs and possibly cats. In addition, the longer chain omega-3 fatty acid, docosahexaenoic acid, may be conditionally essential for normal neurologic growth and development of puppies and kittens. The amount of dietary ALA needed likely depends on the linoleic acid content. Although required amounts of these omega-3 fatty acids are presently unknown, current minimal recommendations include 0.8 g/kg diet of ALA when linoleic acid is 13 g/kg diet (dry-matter basis) for puppies and 0.44 g/kg diet ALA when linoleic acid is 11 g/kg diet (dry-matter basis) for adults. Amounts for cats are currently unspecified. EFA deficiencies are extremely rare in dogs and cats fed complete and balanced diets formulated according to AAFCO profiles. Deficiencies of EFA induce one or several signs, such as a dry, scaly, lusterless coat; inactivity; or reproductive disorders such as anestrus, testicular underdevelopment, or lack of libido. Fatty acid supplements are often recommended for dogs with dry, flaky skin and dull coats, but underlying metabolic conditions should always be evaluated first.
Carbohydrates and Crude Fiber:
Carbohydrates in pet foods include low- and high-molecular-weight sugars, starches, and various cell wall and storage nonstarch polysaccharides or dietary fibers. The 4 carbohydrate groups functionally are absorbable (eg, monosaccharides such as glucose and fructose), digestible (eg, disaccharides, some oligosaccharides), fermentable (eg, lactose, some oligosaccharides), and nonfermentable (eg, fibers such as cellulose, which is an insoluble fiber). Different carbohydrate sources have varying physiologic effects. In cats, carbohydrates apparently are not essential in the diet when ample protein and fats supply glucogenic amino acids and glycerol. Properly cooked nonfibrous carbohydrates are utilized well by dogs. In both dogs and cats, if starches are not cooked, they are poorly digested and may result in flatulence or diarrhea. Except for the occasional case of lactose or sucrose intolerance, most cooked carbohydrates are well tolerated. There is evidence that fermentable sources of carbohydrates (ie, digestible or soluble fibers) are useful in dogs; digestible versus nondigestible carbohydrate sources must be evaluated for their unique characteristics and intended purposes. Beet pulp, for example, contains both soluble and insoluble fiber and provides good stool quality in dogs without affecting other nutrient digestibility when included at ≤7.5% (dry-matter basis).
There are several chemical methods to determine the fiber level of a food; all extract the components of fiber to different degrees, which results in different estimates of fiber level for the same feedstuff. Crude fiber consists mainly of cellulose and lignin. It is resistant to hydrolysis by mammalian digestive secretions but is not an inert traveler through the GI tract. Increased levels of crude fiber in feline rations increase fecal output, normalize transit time, alter colonic micro flora and fermentation patterns, alter glucose absorption and insulin kinetics, and at high levels, can depress diet digestibility.
Stay tuned for part 3 with a discussion about vitamins and minerals.
Notes: Contribution Merck Veterinarian Manual