top of page

Good Fats and Bad Fats

Traditionally, when the term “bad fats” has been used, it was generally referring to saturated fats.  In the late 20th century, saturated fats (meat, dairy, coconut oil) received a lot of bad press in human health based on a scientific study which linked consumption of saturated fat with increased risk of heart disease, stroke etc.  However this research has been debunked.  

  • In 2010, a meta-analysis of prospective epidemiologic studies showed that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of coronary heart disease, stroke, and cardiovascular disease (Siri-Tarino et al., 2010).


Indeed, saturated fats provide the building blocks for cell membranes and hormones, are carriers for the fat-soluble vitamins A, D, E and K, and help lower cholesterol. 


What needs to be considered in evaluating pet food is the quality of the fat. 



The majority of fat used in most dry, extruded dog food is rendered fat.  The fat source can be of either animal or vegetable origin or often a mixture of both.  Labeling is often vague, such as just ‘animal fat’.    For dry, extruded pet food made in the US, AAFCO even permits the inclusion of diseased meat, animals treated with medication (e.g. antibiotics), euthanised animals, and oil or grease from restaurants (fat which is repeatedly heated to a high temperature).   In the EU there are stricter regulations.

To make extruded dry food, rendered ingredients are cooked under a high heat and pressure.  Rendered fat is sprayed on the extruded product comprising the dry food (kibble), which improves palatability. 


This creates two issues (at least!):

  • oxygenation

  • heating.


Oxygenation is what happens when fats are exposed to the air. 


Good fats like marine fats are high in omega 3 polyunsaturated fatty acids (PUFAs).  Omega 3s are highly prone to oxidation due to their large number of double bonds and their position within the fatty acid chain.  They rapidly oxidize during storage to a complex chemical soup of lipid peroxides, secondary oxidation products, and diminishing concentrations of unoxidised fatty acids.  For a detailed explanation of the oxidation process see Albert et al., 2013).  The rate of lipid peroxidation is influenced by light, heat, and oxygen concentration even at normal room conditions. 


All fats can oxidise and become rancid, creating free radicals.  To contain and neutralise free radicals, the body must use antioxidants such as vitamin A, C, D and E.  If the amount of free radicals in the body overwhelm the body’s capacity to regulate them, this leads to oxidative stress, which leads to disease.


In order to stop oxygenation and prevent inevitable fat breakdown, kibble is sprayed with synthetic chemicals.  Of concern, is the use of buylated hydroxyanisole (BHA) and buylated hydroxytoluene (NHT) – although they are powerful in their antioxidant effect, their links to carcinogenicity are concerning (see Brady, 2021).  


Numerous studies confirm that the heating of fat reduces the quality of fat.

  • In a 2010 study examining the effect of rendering on the fat and protein content on raw animal by-product when it is made into meat meal (contained in dry pet food).  It was found that rendering:

    • caused an increase in the saturated to unsaturated fatty acid ratio – that is, a decrease in both linoleic and linolenic acids content and the increase in palmitic and stearic acids content.

    • caused a decrease in amino acid content, because of a significant decrease in lysine, methionine, threonine, leucine, valine, phenylalanine, cystine, serine and aspartic acid.

(Perez Calvo et al., 2010)

What does ZIWI use as a preservative?

ZIWI Peak air-dried food is a shelf stable product. It uses a combination of low moisture, citric acid, mixed tocopherols, and lecithin to ensure this stability. Citric acid’s main purpose in pet food is as a fat preservative. This is particularly important for pet food that has high levels of crude fat, such as ZIWI Peak. The amount used in pet food is very, very small, and is a naturally sourced preservative. Mixed tocopherols (vitamin E) inhibit the oxidation of fats in the product, while also providing additional antioxidant supplementary benefits, particularly regarding polyunsaturated fatty acids.​  Lecithin is used as an emulsifier to prevent the fat from separating in the product, which can visually result in a “fat bloom”.  When consumed in the diet, lecithin is converted into acetylcholine, a substance that transmits nerve impulses. Studies in human trials show that lecithin can modify the cholesterol homeostasis in the liver, which then increases the activity of HMG-CoA reductase and cholesterol 7-alpha-hydroxylase, in turn decreasing the microsomal ACAT activity (LeBlanc et. al., 2003). It can reduce the excess of LDL cholesterol and promotes the synthesis of HDL in the liver (Nicolosi et. al., 2001).

Fishing Boat

Good Fats: Getting the Fat Balance Right

Over recent years, there has been extensive research in both human and pet nutrition exploring the role of polyunsaturated fatty acids (PUFAs) in immune response and health.  In particular, the focus has been on the importance of omega 3s, which are known to have an effect on mediating the inflammatory and immune system responses in the body.

There are two distinct PUFA families, omega-6 and omega-3:

  • Linoleic acid (LA) is the head of the omega-6 family.  The important omega-6 derivatives of LA are gamma-linolenic acid (GLA) and arachidonic acid (AA). 

  • Alpha-linolenic acid (ALA) is the head of the omega-3 family.  The important derivatives of ALA are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). When mammals eat oils or foods that contain LA or ALA, it is theoretically possible for enzymes in their bodies to convert these fatty acids to longer-chain fats with more double bonds — that is, long chain PUFAs (LC-PUFAs).  But in reality, full conversion to LC-PUFAs is an inefficient process.  


This has enormous bearing on which fats are essential for dogs and cats.  Logically, canine PUFA metabolism reflects their carnivore-omnivore status. Canines convert LA to AA more readily than humans do (Lloyd, 1990).  Therefore, dogs do not benefit from large quantities of vegetable oils rich in LA; in fact, this may exacerbate allergic and inflammatory conditions. Vegetable oils are not prevalent in the natural canine diet (Hayek & Reinhart, 1998).

Feline PUFA metabolism is strictly carnivorous. Cats lack some of the enzymes that enable humans and dogs to convert LA to LC-PUFAs. Because cats cannot synthesize AA, their daily requirement for AA is so high that it must be provided in the diet (Bauer, 1997).  DHA is critical for cats, because they cannot make it from LNA, for the same reasons they cannot convert LA to LC-PUFAs (Logas & Kunkle, 1993).


What is the ideal omega-6/ omega-3 ratio for dogs?  AAFCO is not particularly helpful, recommending that the ratio should be less than 30:1.    Research in humans, and into the Mediterranean diet, suggest that a ratio of 5:1 and 4:1 has beneficial impact on inflammatory disease and prevents cardiovascular disease (see Brady, 2021; Martínez-González et al., 2021).​


We can look to the nutrient content of typical wild prey animals for guidance. Paulsen et al (2014) investigated the fatty acid composition of a range of prey animals.  It was found that the omega-6/omega-3 ratios were lower for wild animals (from 2:1 to 8:1), and higher for domesticated animals (11:1 to 13:1). 


Good sources of Omega-3 and Omega-6 fatty acids can be found in wild-caught fish and seafood and free-range grass-fed, grass-finished meat protein.  Animals that are grass-fed and grass-finished retain twice the level of Omega-3 and Omega-6 fatty acids, compared to grain-fed animals.


All meat used in ZIWI Peak recipes comes from New Zealand grass-fed and finished, free-range animals, sustainably sourced and ethically managed.  Furthermore, all ZIWI Peak recipes contain 3% whole New Zealand Green Mussel which is a rich natural source of Omega fatty acids. ZIWI also offers recipes containing Blue Mackerel. These recipes naturally contain higher levels of Omega-3 and Omega-6 fatty acids.   All of ZIWI's recipes meet or exceed the suggested essential fatty acids requirements of AAFCO and the NRC.  You can find the full Typical Analysis of all our recipes at the Ziwi website.


Dogs fed with kibble should be supplemented with omega-3, as dry food is often high in omega-6 and low in omega-3.



STUDY: fatty acids contained in commercial dry dog food vary greatly (from some to none at all!)

Norwegian School of Veterinary Science


Aim: to measure the omega-6 and omega-3 levels of 12 different brands of commercially available dry dog food sold in Norway (large breed puppy in particular)

  • Included Eukanuba (large breed puppy); Proplan (puppy), Hill’s (large breed puppy); Pedigree (puppy); Friskies (puppy); Royal Canine (large breed puppy)



  • analysed for total contents of fat and fatty acid composition.



  • Analysis of the foods showed a wide range of both types of fatty acids.

  • Some foods were almost completely devoid of marine oils (thus low in EPA and DHA)

  • The brands containing “omega-3 fatty acids” were primarily in the form of alpha-linolenic acid (ALA) from plant oils.

    • This is an important finding because often only omega-3 content is reported on the pet food label. If the omega-3 fatty acids are supplied primarily as alpha-linolenic acid, for example from flax, the health benefits that come from EPA and DHA will not be provided by that food (Case, 2020).

  • All brands had sufficient amounts of omega-6 fatty acids (according to NRC recommended levels).

Ref: Alhstrom O, Krogdahl A, Vhile SG, Skrede A 2004, “Fatty acid composition in commercial dog foods”, Journal of Nutrition, vol. 134: 2145S-2147S.


STUDY: nutritional labels on dog food are not always truthful re omega 3

University of Maringa, Brazil


Aim: to compare the fat content reported on the labels of 10 dry extruded dog foods with laboratory-measured profiles of omega-3 fatty acids, DHA and EPA from the foods



  • All 10 foods reported total omega-6 and total omega-3 fatty acid levels.

  • In all 10 foods, chicken fat appeared to be the predominant fat source.


  • Only 5 foods included EPA and DHA content on their product label.

    • BUT NONE actually contained ingredients containing DHA or EPA, and the lipid profiles did not fit with typical oily fish ingredients.Instead ALA (plant based omega-3 fatty acid) was found to constitute the omega 3 content.



The researchers speculate that the EPA and DHA in the samples could have been destroyed by oxidation of the long-chain unsaturated fatty acids during the heat processing of extrusion.  Alternatively, it is possible that the manufacturers of the foods had not included DHA and EPA in the first place.

Ref: Silveria R, dos Santos PDS, Pizzo JS, et al, 2020, “Evaluation of dog food authenticity through lipid profile using GC-FID and ESK-MS”, Journal of Brazilian Chemical Society, vol. 31, No. 12, 2511-2517


STUDY:  “Skin and health” dry dog food labels can be misleading

Tufts University’s Cummings School of Veterinary Medicine, USA


Aim: to examine the nutrient profiles and ingredients list of 24 brands of dog food that all were marketed for skin and coat health – using terms such as “sensitive”, “skin sensitivities”, “digestive sensitivity”, “digestive health”, and “limited/unique ingredients”.  They looked at 15 dry (extruded) foods and 9 canned foods, representing 11 different brand names.




  • Protein source varied widely and included chicken, fish, egg, venison, beef, pork, duck, lamb, soy, peas, and turkey.

    • Thus not appropriate for an elimination diet

  • Carbohydrate sources varied widely and included rice, potato, wheat, oats,barley,millet, corn, quinoa and tapioca.

  • There were 22 diets that promoted inclusion of omega-6 or omega-3 fatty acids or that promoted inclusion of omega fatty acids used vague terms such as “omega fatty acids” or “omega oils”, rather than specifying which fatty acid was contained.When EPA and DHA were listed, the amounts included were similar to that found in dry food not labelled for skin/coat health.


Conclusions: The researchers concluded that the wide variety of ingredients and large range in nutritional value of products marketed for skin and coat health make product selection for owners who are interested in these foods confusing.

Ref: Johnson LN, Heintze CR, Linder DE & Freeman LM 2015, “Evaluation of marketing claims, ingredients, and nutrient profiles of over-the-counter diets marketed for skin and coat health of dogs”, Journal of the American Veterinary Medical Association, vol. 246, pp 1334-1338.

A diet high in essential fatty acids is also essential for the pregnant and lactating bitch, and for the growth and development of her puppies.

Puppies more about the fat tolerance of dogs in
part 3 of our article... 
Dog Sledding
bottom of page