Bioavailable Nutrients in Fresh Foods

Fresh food is best but when creating a home prepared diet for a carnivorous species, there are multiple nutrient variables to consider. Although a certain food can provide specific nutrients, it may not be in the ideal amounts or in a bioavailable form.

There is a total of six nutrients that fall within this topic:

Animal Protein vs. Plant Protein

Most will agree that animal protein is superior to plant protein when feeding a dog and cat a home prepared diet. However, there is the occurrence of vegetarian and vegan foods manufactured for dogs and cats. Pet owners should be mindful of these foods and how nutrient bioavailability can impact long term health.

Digestibility of animal proteins is significantly higher than plant proteins and they provide readily available amino acids for biological function, muscle development, and maintain muscle integrity. This is not to say that plant sources do not provide protein or amino acids.

Plant sources do provide protein and amino acids but they are less digestible than animal sources. This is entirely due to the fiber, particularly cellulose, that is present in plant sources. This fiber is bound to protein which lowers the digestibility and therefore lowers the total available protein and amino acids that can be absorbed.

Digestible Indispensable Amino Acid Score (DIAAS) is a system utilized to measure protein quality in human grade foods. In human modeled studies DIAAS was 11% higher in the groups consuming an omnivorous diet in comparison to a vegetarian diet. Furthermore, the total available Protein was 43% higher in the omnivorous diets in comparison to the vegetarian diets. Although dogs and cats are carnivores, this data can be postulated for these species as well.

Additionally, it is important to note that Taurine is an essential amino acid that is required for cats which cannot be found in plant sources in adequate levels to fulfill biological needs. Therefore, animal protein is significantly important to cats.

Based on this information, it can be easily concluded that utilizing animal sources for essential protein and amino acids is the ideal choice when creating a home prepared diet for a dog and cat. Furthermore, this point sets the tone for all other variables to be considered when selecting fresh foods for bioavailable nutrients.

EPA+DHA vs. ALA

Alpha-Linolenic Acid (ALA) is the plant based omega 3 that is the precursor of the long-chain omega 3 Eicosapentaenoic Acid (EPA), Docosapentaenoic Acid (DPA), and Docosahexaenoic Acid (DHA). ALA food sources are often recommended as an alternative source to omega 3 fatty acids for dogs and cats who cannot consume the food sources of EPA and DHA.

While ALA is the precursor to EPA and DHA, the conversion rate is low. There are multiple studies (1,2,3) that have concluded that conversion of ALA to EPA is between 2% and 8% in healthy adults but is reduced by 40-50% in diets high in omega 6. Additionally, these studies have concluded that conversion of ALA to DHA is between 0% and 4%.

The food sources that provide concentrated amounts of ALA fatty acids include hemp seeds, flax seeds, and chia seeds (including all oils, ie: hemp seed oil); and the food sources that provide concentrated amounts of EPA/DHA include animal proteins such as fish (including fish oils, ie: fish oil) and shellfish but pasture raised eggs contribute moderate levels of omega 3 fatty acids. It can be challenging to provide sufficient levels of EPA and DHA in a home prepared diet when food allergies and intolerances are a factor.

Algae Oil is the only alternative to fish and shellfish when providing sufficient levels of EPA and DHA in a home prepared diet. This alternative ingredient is relatively new to the pet food sector however there are studies confirming its safety and bioavailability in dogs. Algae Oil dosages are listed below based on the safety and efficacy studies conducted on dogs. It is important to note that studies conducted on cats are not available at this time.

Heme Iron vs. Non-Heme Iron

Both animal and plant food sources provide iron; however it is important to differentiate between the two types of iron available in all foods. Dietary iron has two forms – heme iron and non-heme iron. Heme iron is available in hemoglobin and myoglobin within animal food sources whereas non-heme iron is available in plant food sources.

While there are many plant sources high in iron, this type of iron is not the ideal source of iron for dogs and cats. The conversion of non-heme iron to heme iron in human models is 2% to 20% whereas heme iron from hemoglobin has a bioavailability of 90% in dogs and 70% in cats. The study on the heme iron bioavailability was done using a hemoglobin concentrate versus a fresh food source; therefore it can be concluded that the bioavailability is higher than what is currently reported (especially for cats).

Plant food sources are often recommended to meet iron requirements in home prepared food for dogs and cats. The common recommendations include wheatgrass, spinach, kale, and broccoli which all do provide iron; however the iron is non-heme which means the bioavailability is poor for dogs and cats. Therefore it is recommended to rely upon animal sources to meet iron requirements when using fresh foods.

All animal protein (including seafood) provides heme iron however iron concentrations vary among different ingredient options:

An iron supplement is recommended in diets where food allergies, budget restrictions, and/or sourcing accessibility makes it difficult to include the animal sources that are concentrated in heme iron.

Copper from Ruminant, Fowl, & Poultry Liver vs. Copper from Monogastric Liver

Liver and shellfish are the two food sources that are concentrated in copper. However there are some variables to consider when feeding liver as the fresh food ingredient to supply copper. This is because not all liver options provide the same quantity and bioavailability of copper.

There are four categories for identifying the nutritional differences among different liver options:

The liver from monogastric mammals have been studied to identify copper content and bioavailability. The mechanism as to why the copper found in the liver of these animals is not bioavailable remains unknown. However, this information is important when creating a home prepared diet.

Relying on a monogastric liver ingredient as the copper source in a home prepared diet will cause nutritional deficiencies in the long run. Therefore, it is highly recommended to rely upon a ruminant or fowl liver source in a home prepared diet to ensure sufficient amounts of copper is provided and it is provided in a source with high bioavailability.

A copper supplement is recommended in diets where food allergies, budget restrictions, and/or sourcing accessibility makes it difficult to include a ruminant or fowl liver that are concentrated in copper.

Retinol vs. Beta-Carotene

Beta-carotene is a carotenoid that gives plants their red-orange pigment where it can be converted to retinol (vitamin A) after ingestion in humans. This model has been tested in both dogs and cats where it is only applicable to dogs.

Multiple studies have shown that dogs can successfully convert beta-carotene into vitamin A which means that animal based sources for retinol do not need to be relied upon for long term feeding when beta-carotene rich foods are fed in adequate amounts. However, cats must rely upon an animal based food source for vitamin A because they are unable to convert beta-carotene to vitamin A.

Whole food sources for retinol are limited to two options which are liver and cod liver oil. It is highly encouraged to utilize liver for retinol in home prepared diets for dogs because liver provides many other essential nutrients (copper) to avoid the need of supplementation. However, if a dog refuses to consume liver of any kind, raw or cooked, then the inclusion of cooked sweet potato and carrots are the alternative options for beta-carotene.

Unfortunately there are no other fresh food alternatives for liver or cod liver oil to provide cats with sufficient amounts of vitamin A in a home prepared diet. A vitamin A supplement is recommended if these ingredients are not fed.

Cholecalciferol (Vitamin D3) vs. Ergocalciferol (Vitamin D2)

There are two forms of vitamin D, cholecalciferol (D3) and ergocalciferol (D2). D3 is found in animal sources and D2 is found in plant sources and fortified foods. Additionally, D2 must be converted to D3 in the liver after digestion in order to be absorbed and utilized by the body.

Multiple studies have shown that dogs can successfully convert D2 into D3 which means that animal based sources for vitamin D do not need to be relied upon for long term feeding when D2 rich foods are fed in adequate amounts. However, cats must rely upon an animal based food source for vitamin D because they are unable to convert D2 to D3.

Whole food sources that are concentrated in D3 are limited to a few options which are fatty fish and cod liver oil. Food sources with moderate amounts of D3 include pasture raised pork and egg yolks.

It is highly encouraged to utilize D3 food sources in home prepared diets for dogs because they provide many other essential nutrients to avoid the need of supplementation. However, if a dog cannot eat these ingredients due to protein allergies/intolerances, budget restriction, and/or sourcing accessibility then the inclusion of a D2 source can be fed to dogs to fulfill their vitamin D requirements. 

Mushrooms are the only plant source that provides vitamin D2. However, the only way for mushrooms to provide this benefit is if their gills are exposed to UV light for 15-30 minutes. It is important to remember that the levels of vitamin D2 in UV-exposed mushrooms may decrease with storage and cooking; but the D2 level is likely to remain above 10 μg/100 g fresh weight.

Unfortunately there are no other fresh food alternatives for fatty fish, cod liver oil, pasture raised pork, and egg yolks to provide cats with sufficient amounts of D3 in a home prepared diet. A vitamin D supplement is recommended if these ingredients are not fed.