Fat in a raw diet
This article is part of the series in which we explore the science of nutrition. In the previous article of the series, we started talking about macronutrients and protein in particular. In today’s article, we are going to discover another macronutrient: lipids. We will see what they are, what the feline requirements are, and we’ll talk about different controversial sources of lipids such as olive oil or coconut oil.
What are lipids?
Dietary fats—also called lipids—are compounds that are soluble in organic solvents (like alcohol), but are insoluble in water. Generally, lipids that are solid at room temperature like butter are called fats, while lipids that are liquid at room temperature are called oils.
They can be categorized into simple lipids, compound lipids, and derived lipids.
Simple lipids
Examples of simple lipids are waxes and triglycerides. Triglycerides are the ones that are going to interest us as they are the most common form of lipids in the diet of our cats.
In the same way that amino acids are the building blocks of proteins, fatty acids are the building blocks of triglycerides. In fact, each triglyceride is made of 3 fatty acids and a glycerol molecule.
Fatty acids have a carbon chain that can vary in length. So they can be divided into 3 categories, depending on the number of their carbons:
Short-chain fatty acids (2 to 6 carbons), or SCFA: we talked about their benefits in the article about fibers.
Medium-chain fatty acids (8 to 12 carbons).
Long-chain fatty acids (more than 14 carbons)
In a diet, most fatty acids are long-chain.
Fatty acids can also be categorized based on their bounds between the carbons:
Saturated fatty acids (SFA) don’t contain double bonds between the carbons (so they are “saturated” with hydrogen).
Monounsaturated fatty acids (MUFA) have one double bond between the carbons.
Polyunsaturated fatty acids (PUFA) have two or more double bonds
Fatty acids in plant oils are mainly unsaturated (80-90%), while animal fats are mostly saturated (40-60%).
Finally, unsaturated fatty acids can be classified depending on the position of their first double bond. If the first double bond is located in the third position, they are called omega-3, often written as n-3 or ω−3. Similarly, the first double bond of an omega-6 or an omega-9 will be respectively in the 6th and 9th position.
Compound and derived lipids
Compound lipids are lipids linked to non-lipid molecules such as lipoproteins, glycolipids, or phospholipids.
Derived lipids are—for example—steroids like cholesterol and some hormones like estrogen. Other examples of derived lipids are fat-soluble vitamins A, D, E, and K.
What’s the role of lipids?
Fats have various functions in the cat's body. Firstly, they are an energy source, as fats bring twice more energy than proteins or carbohydrates. As we have seen in the article about energy, one gram of fat brings 8.5 kcal.
Fat is also the primary form of stored energy in the body. In fact, fat accumulates under the skin and around vital organs to be used in case of starvation or extended exercise. The stored fat also provides insulation and protection against injury for the major organs.
Like proteins, fat also has various metabolic functions. In fact, compound lipids are components of the cell membranes and participate in the transport of nutrients across the cell membranes.
Cholesterol is necessary for the proper digestion and absorption of fats.
Fat is also a source of essential fatty acids as we will see below, as well as necessary for the absorption of the fat-soluble vitamins (vitamins A, D, E, K).
Finally, fats, like proteins, are important for the palatability of the diet.
Essential fatty acids
Some fatty acids are said to be essential because they can’t be made in the body, and so they have to be provided in the diet. These essential fatty acids are all long-chain and polyunsaturated fatty acids from the omega-6 and omega-3 families.
The essential omega-6 fatty acids are linoleic acid (LA) and arachidonic acid (AA).
The essential omega-3 fatty acids are alpha-linolenic acid (ALA), EPA, and DHA.
Essential fatty acids are the precursors of hormone-like compounds that have various roles. For example, linoleic acid is important for skin health. EPA and DHA are important for the immune system, and DHA is important for neurological and visual development during pregnancy and growth. Other roles of the essential fatty acids include regulation of body temperature, regulation of blood clotting mechanisms, and control of inflammation.
Both omega-6 and omega-3 have major roles, but because they use the same metabolic pathways it’s important to keep a balance between the two. The current recommendation is to keep the omega-6 to omega-3 ratio between 2:1 to 10:1.
So, linoleic acid is a precursor of arachidonic acid (an omega-6, C20:4n-6).
The alpha-linolenic acid is a precursor of EPA (the eicosapentaenoic acid, an omega-3, C20:5n3) and DHA (the docosahexaenoic acid, an omega-3, C22:6n3).
However, cats have a very limited capacity to synthesize these fatty acids: that’s why the arachidonic acid, EPA, and DHA are essential for cats and should be provided in the diet.
Fat requirements
Now, let’s look at the numbers for the fat recommendation:
The minimum NRC recommendation is 22.5 g of fat per 1000 kcal, equivalent to 19% of the calories coming from fat or 9% fat on the dry matter (DM) for a 4000 kcal/kg diet.
If we look at the data on wild cats, they hunt prey containing 30 to 68% of calories coming from fat, and on average feral cats consume 46% of calories from fat.
A general recommendation for adult cats would be to provide around 30 to 40-45% of the calories from fat, as higher fat content may not be appropriate for our domestic cats which aren’t as active as feral cats. As we already said, fat is important for palatability so if the fat amount is too low in the diet your cat may refuse to eat it.
- Linoleic acid: the NRC recommendation is 1.4 g per 1000 kcal, equivalent to 0.55% on the dry matter (DM) for a 4000 kcal/kg diet.
- Arachidonic acid: the NRC recommendation is 15 mg per 1000kcal.
- Alpha-linolenic acid: there is no recommendation for adult cats.
- EPA + DHA: the NRC recommendation is 25 mg per 1000 kcal with a majority of EPA. It’s equivalent to 0.01% on the DM.
Keep in mind that we are still lacking information on the exact recommendation for fatty acids, especially for EPA and DHA which are often still considered conditionally essential, and that it’s also important to keep a balance between omega-6 and omega-3.
Fat deficiency and excess
The maximum recommendation or safe upper limit is 82.5 g of fat per 1000 kcal, equivalent to 70% of the calories coming from fat or 33% fat on the DM. This limitation isn’t caused by the toxicity of fats per se, but if you have too many calories coming from fat the diet won’t contain enough protein. Additionally, as fat is high in calories (x2 more than proteins) a high-fat diet will also be very energy-dense, meaning that all the other nutrients will need to be quite concentrated to avoid nutrient deficiencies. And finally, as the diet will be high in energy, it can easily lead to obesity.
Excess fat can also result in diarrhea or fatty stools.
Polyunsaturated fatty acids are fragile and can easily become rancid if they are stored at a high temperature or in a humid environment. When the fatty acids become rancid they lose their capacity and become unpalatable. If high levels of PUFA are fed without adding antioxidants such as vitamin E, it may result in pansteatitis or “yellow fat disease.”
The deficiency in fatty acids causes impaired wound healing, a dry and dull coat, hair loss, skin lesions, or hot spots. It can also cause neonatal abnormalities or death, as well as growth abnormalities in kittens. Finally, a deficiency in omega 3 can cause nervous system and retinal abnormalities, as well as a reduction in learning capabilities and memory.
Where do you find fatty acids?
Linoleic acid (LA) is found in high quantities in plant oil such as safflower oil, sunflower oil, but also in animal fats, especially from poultry. It’s rare that you need to supplement it in your cat's diet.
Arachidonic acid (AA), is found exclusively in animal based-food. Chicken is especially high in arachidonic acid, it also rarely needs to be supplemented in the diet.
Alpha-linolenic acid (ALA) is found in some plant oils such as flaxseed oil or canola oil, and in lower quantities in animal fats. It also rarely needs to be supplemented, especially because there are no requirements for adult cats. If you want to balance the omega-6 to omega-3 ratio it’s more interesting to use EPA and DHA as they are more potent than ALA.
EPA and DHA, are mainly found in marine products such as oily fish, fish oil, or algae oil. DHA can also be found in brains. Generally, EPA and DHA must be supplemented as meat products won’t be enough to provide them as well as to balance the omega-6 to omega-3 ratio.
Olive oil is often added to homemade diets. However, it contains only 7% linoleic acid and no other essential fatty acids. The omega-6:omega-3 ratio is 14:1 which is above the recommended ratio. For these reasons, it’s not an oil that I would recommend adding to your cat’s diet.
Coconut oil is also a very popular addition to a raw diet, but it doesn’t contain essential fatty acids. It contains medium-chain triglycerides (MCT): these fatty acids aren’t digested in the same way as long-chain fatty acids and may have therapeutic effects. However, there aren't many long-term studies on cats at the moment, so I wouldn’t recommend using it for dietary purposes.
The takeaway from this article is that fat is an essential component of a raw diet. However, a diet high in fat will need to be nutrient-dense and can lead to obesity. In a common prey model raw diet, the requirement for the essential fatty acids LA, ALA, and AA will be covered, but a supplement such as fish or fish oil is needed for EPA and DHA as well as to lower the omega-6:omega-3 ratio.
Fat in raw meat
| Cut | g of lipids / 100g as fed | g of lipids / 1000kcal | % of calories coming from lipids |
|---|---|---|---|
| Chicken breast | 2.6 | 22 | 19 |
| Chicken breast with skin | 9.3 | 54 | 46 |
| Beef brisket point | 21.0 | 79 | 67 |
| Beef chuck stew meat | 4.5 | 35 | 30 |
| Ground beef 10% | 10.0 | 57 | 48 |
| Ground beef 20% | 20.0 | 79 | 67 |
| Ground beef 30% | 30.0 | 90 | 77 |
| Duck breast | 29.4 | 86 | 74 |
| Lamb shoulder chop | 20.9 | 80 | 68 |
| Pork leg shank | 12.0 | 62 | 53 |
| Pork tenderloin | 3.5 | 29 | 25 |
| Turkey breast | 2.3 | 20 | 17 |
| Turkey thigh with skin | 9.2 | 57 | 48 |
| Veal escalope | 2.6 | 24 | 20 |
| Veal shoulder | 4.6 | 37 | 32 |
| Venison | 2.4 | 20 | 17 |
If the number is in red, the meats are high in fat (>15%).
If the number is in yellow, the meats are moderate in fat (~10).
If the number is in green, the meats are lean and contain 5% of fat or less.
Essential fatty acids in oil and meat
| Food | Linoleic acid (omega-6) | Arachidonic acid (omega-6) | Alpha-linolenic acid (omega-3) | EPA (omega-3) | DHA (omega-3) | Ratio omega-6:omega-3 |
|---|---|---|---|---|---|---|
| Oil | ||||||
| Sunflower oil | 56 | 0 | 0.1 | 0 | 0 | > 100 |
| Walnut oil | 56 | 0 | 11.9 | 0 | 0 | 5 |
| Corn oil | 54 | 0 | 1.0 | 0 | 0 | 52 |
| Soybean oil | 52 | 0 | 6.9 | 0 | 0 | 7 |
| Wheat germ oil | 47 | 0 | 5.9 | 0 | 0 | 8 |
| Flaxseed oil | 14 | 0 | 53.3 | 0 | 0 | < 1 |
| Canola oil | 19 | 0 | 7.5 | 0 | 0 | 2 |
| Olive oil | 7 | 0 | 0.7 | 0 | 0 | 10 |
| Coconut oil | 2 | 0 | 0 | 0 | 0 | |
| Sardine oil | 0 | 0 | 0 | 10 | 11 | < 1 |
| Salmon oil | 0 | 0 | 0 | 13 | 18 | < 1 |
| Ingredients | ||||||
| Chicken breast | 0.32 | 0.05 | 0.01 | 0 | 0 | 15 |
| Chicken breast with skin | 1.74 | 0.05 | 0.08 | 0.01 | 0.02 | 15 |
| Chicken heart | 1.91 | 0.72 | 0.07 | 0 | 0 | 37 |
| Beef brisket point | 0.44 | 0.02 | 0.23 | 0 | 0 | 2 |
| Beef chuck stew meat | 0.23 | 0.05 | 0 | 0 | 0 | 46 |
| Ground beef 10% | 0.26 | 0.04 | 0.04 | 0 | 0 | 8 |
| Ground beef 20% | 0.42 | 0.04 | 0.05 | 0 | 0 | 9 |
| Ground beef 30% | 0.58 | 0.04 | 0.07 | 0 | 0 | 10 |
| Lamb shoulder chop | 1.20 | 0.07 | 0.37 | 0 | 0 | 3 |
| Pork brain | 0.09 | 0.47 | 0.12 | 0 | 0.45 | < 1 |
| Pork leg shank | 2.11 | 0.08 | 0.09 | 0 | 0 | 22 |
| Pork tenderloin | 0.46 | 0.05 | 0.02 | 0 | 0 | 33 |
| Sardine | 0.10 | 0 | 0.47 | 1.09 | 1.58 | < 1 |
| Salmon | 0.17 | 0.27 | 0.30 | 0.32 | 1.12 | < 1 |
| Turkey breast | 0.26 | 0.05 | 0.02 | 0 | 0 | 14 |
| Turkey thigh with skin | 2.12 | 0.09 | 0.14 | 0 | 0.01 | 14 |
| Veal escalope | 0.63 | 0.22 | 0.04 | 0.04 | 0.01 | 9 |
| Veal shoulder | 0.34 | 0.06 | 0.01 | 0 | 0 | 30 |
| Venison | 0.31 | 0.10 | 0.07 | 0 | 0 | 6 |
Other readings
Ultimate guide to fats from Feed Thy Dog (with a focus on dog)
Essential fatty acids by Fed to Thrive (with a focus on dog)
Sources
Linda P. Case et al. 2015. Canine and Feline Nutrition.
National Research Council. 2006. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press.
Eisert R. Hypercarnivory and the brain: protein requirements of cats reconsidered. J Comp Physiol B. 2011;181(1):1-17.
Plantinga EA, Bosch G, Hendriks WH. Estimation of the dietary nutrient profile of free-roaming feral cats: possible implications for nutrition of domestic cats. Br J Nutr. 2011;106 Suppl 1:S35-S48.
Sources for the table
USDA
CIQUAL