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PROTEIN

14 Jan 2024

Protein is critical for optimal health because it provides indispensable amino acids for our body cells, facilitating communication and synergistic activities.

 

Body processes such as inflammation responses, mitochondrial activity, and satiety are highly dependent on the correct amount of available amino acids. They exert their influence through signaling systems including mammalian/ mechanistic target of rapamycin complex 1 (mTORC1), general control nonrepressed 2 (GCN2), glucagon-like peptide 1 (GLP-1), peptide YY (PYY), serotonin, and insulin.

 

The progression of several veterinary medical conditions, such as renal disease, liver failure, and urolithiasis is also altered by dietary amino acids.

All body protein is composed of 20 different amino acids, of which 10 cannot be made by the dogs’ body system and 11 cannot be made by the cats’ body system.  

 

The correct type of protein eaten provides these 10 to 11 essential amino acids (EAAs) for making new proteins and an array of other supportive metabolic functions in the body.

Protein assessment in food has evolved through the years.

 

The main aim has always been to identify the most cost-effective, high-quality, easily digestible, and absorbed dietary protein available, with the least possible impact on our environment.

Some of the past methods included protein efficiency ratio (PER), biological value (BV), net protein utilization (NPU), protein digestibility corrected amino acid score (PDCAAS), digestible indispensable amino acid score (DIAAS), and more recently, Essential Amino Acid-9 (EAA-9) score which can compare protein quality for single ingredients, multi-ingredient foods, and all the meals eaten in a day.

 

Unfortunately, the current nutritional labels on most food products erroneously suggest that all proteins (whether they are from animals/ plants/ dairy/ insects) are equivalent and thus, interchangeable.

They are not.

The amino acids that cannot be synthesized from metabolic intermediates are known as EAAs.

 

These amino acids must be supplied from eating protein because the body does not have the necessary metabolic pathways to make these amino acids.

HUMAN (9 EAAs)

 

Histidine

Leucine

Isoleucine

Lysine

Methionine

Phenylalanine

Threonine

Tryptophan 

Valine

ESSENTIAL AMINO ACIDS (EAAs)

DOG (10 EAAs)

Histidine

Leucine

Isoleucine

Lysine

Methionine,

Phenylalanine,

Threonine

Tryptophan 

Valine

Arginine

CAT (11 EAAs)

 

Histidine

Leucine

Isoleucine

Lysine

Methionine

Phenylalanine

Threonine

Tryptophan 

Valine

Arginine

Taurine

Studies have shown that pet dogs and cats can be sustained by feeding elemental amino acids.

But sustainability does not always equate to optimum health

WHICH PROTEIN?
PLANT vs ANIMAL vs LAB vs INSECT

Feeding the right dietary protein will ensure that the health of our pet dogs and cats can be sustained at an optimum level through their lives.

Taurine, the 11th essential amino acid (EAA) needed by cats can only be found in animal proteins and some insects.

Research done on humans showed that eating either animal protein or plant protein will increase the average synthesis of lean muscle mass and increase overall strength.

 

However, even in these human studies, plant proteins have exhibited lower digestibility, due to the presence of the antinutritional factors (ANFs), when compared to animal proteins, such as meat, poultry, egg, and milk.

 

Manufacturers of pet food have engaged scientists and researchers to demonstrate that the inadequacies of plant-based proteins used in conventional pet food like common deficient in one or two essential amino acids and their low protein nutritional value, can be overcome through protein complementation, such as the mixing of cereals and legumes, or a variety of plants; and by employing adequate processing steps, such as cooking, boiling, extrusion to improve the digestibility through inactivation or reduction of the presence of the ANFs.

assorted-colored bean lot_edited.jpg

Some common high-protein plant foods include tofu, tempeh, edamame, lentils, chickpeas, peanuts, almonds, nutritional yeast, quinoa, buckwheat, and chia seeds.

 

Amongst them, quinoa, buckwheat, soybean, and soybean products such as tofu, edamame, and tempeh have the 10 essential amino acids needed by dogs.

Cats are obligate carnivores that are considered not efficient at digesting the fibrous and complex structural matrix of plant-based food and cannot make taurine from cysteine and methionine which are available in grains and legumes.

PLANT-BASED PROTEIN 

One gram of animal-based protein contains an average of 4 calories; therefore, you need to make sure that you are not overfeeding your pet if you are supplementing them with cooked animal-based protein.

Overall, animal proteins are of a higher quality because they not only contain all the dietary EAAs, but they also have the highest amounts of them that are the easiest for the pet to digest and absorb, especially for iron, B vitamins, and fat, when compared to plant proteins.

ANIMAL-BASED PROTEIN

Animal-based proteins that are easy to digest and absorb include eggs, fish, lean chicken, and beef meat.

 

Cooking meat between 70 - 75*C also enhances digestibility by exposing the cleavage sites of the meat tissue to the digestive enzymes in the gut system.

Lab-grown meat, also known as cultivated, cell-based, or hybrid protein, uses a culture medium to nurture and grow stem cells harvested from the fat or muscle of any animal. The medium (with the specific cell) is then put into a bioreactor which supports the cells’ transformation into an end product that looks and tastes like traditional meat.

As of June 2023, the US and Singapore are the only 2 countries that allows the sales of these cultivated meat for human consumption.

CELL-BASED PROTEIN (Cultured Meat)

The culture medium and bioreactor are expensive to produce and thus the cultured meat is not cheap.

 

Lab-grown meat has also been approved for pet consumption in the EU on 8 November 2023. The manufacturer of the registered product for pets claimed to be “cultivated cells of mammalian origin”- but the company has not disclosed which mammalian animal is the actual source.

As of now, we can only guess.

There are at least 2,000 different edible insect species known, excluding those that may be bred exclusively for feedstuff or other industrial uses.

Even though entomophagy (insect eating) has been a traditional cuisine in many areas of the world for past centuries, nutritional data is somewhat scarce and scattered.

 

Recent studies confirm that the nutritional value, limiting amino acids, and bioavailability of insects are highly variable between species, habitats, and life stages.

 

Based on reports from observations by biologists, wild cats do consume insects - but they make up less than 5% of their overall diet. Not enough insects were eaten by wolves for the biologists to document it as a significant portion of their diets. Thus, the pet food industry will need to gather more evidence to back their claims that insect protein is a natural part of dogs’ and cats’ ancestral diets.

 

If mammals (specifically pet cats and dogs) did not evolve to eat insects, can we be sure that our pet dogs and cats can thrive by substituting their dietary protein with insects?

INSECT-BASED PROTEINS

Studies have indicated that whole adult insects are of especially low quality because of the presence of chitin, a polymer of N-acetyl-d-glucosamine that is like plant cellulose, in their exoskeletons, which may hinder protein digestion.

 

The limiting amino acids in some insects mean that they cannot be fed without other additional protein or EAA supplementation to ensure that the dogs and cats receive a complete meal.

 

For example, the black soldier fly larvae cannot be fed as the only protein source for both dogs and cats because of their limiting EAA, methionine.

 

Farming and processing of edible insects for food and feed has no predetermined internationally accepted or regulated protocol or industry standard – in developing countries, many insects consumed by humans are still collected in the wild, natural habitat.

The common species farmed in Europe, North America, and parts of Asia for pet food are the house crickets and yellow mealworms.

 

Some studies identified proteins like aginine kinase and tropomyosine, and enzymes like α-amylase which are common allergens linked to edible insects. 

 

The insects for pet food can be farmed on substrates like animal manures (from poultry, pig), organic industrial, and/or domestic wastes (e.g. brewery and supermarket, food processor wastes), and pre-composting anaerobic residues.

 

With the array of concerns with entomophagy, policies to guarantee hygienic and safe farming, production, processing, and consumption of insects for both humans and animals will have to be established by the international community to produce a food source (insects and their derivatives) that is truly safe and beneficial to our health while leaving a small carbon foot print.

As of 2023, pet food sold in the USA is regulated by the Food and Drug Administration (FDA) while the Association of American Feed Control Officials (AAFCO) establishes a model that states minimum requirements and relevant governing bodies can adopt these requirements for legislation purposes.

AAFCO requires manufacturers to provide a guaranteed analysis of 4 items on the pet food packaging:

1.    Crude Protein (minimum percentage)
2.   Crude Fat (minimum percentage)
3.   Crude Fiber (maximum percentage)
4.   Moisture (maximum percentage)

 

In the UK, similar pet food nutritional guidelines for manufacturers are planned by the European Pet Food Industry (FEDIAF) and Food Standards Agency (FSA). They legislate that their analytical constituents printed on food labels must include similar nutrient percentage compositions as stated by AAFCO, plus an additional Crude Ash (mineral content) percentage and listed ingredients on a pet food label must be arranged in descending order by weight. 

In Australia, this is governed by the Pet Food Industry Association of Australia (PFIAA) with similar requirements.

In New Zealand, the Ministry for Primary Industries regulates pet food manufacturing under their Agricultural Compounds and Veterinary Medicines (ACVM) Act 1997 as oral nutritional compounds and the Animal Product Act 1999 (which is required by NZ law).

WHAT TO BUY?

However, the guaranteed crude protein percentage analyzed for a pack or canned food does not necessarily equal the same level of bioavailable, good-quality protein.

 

These are also not the actual, true percentage of the nutrients - but a “not less than” and “not more than” estimation.

In the case of guaranteed crude protein, the numerical result is derived from the food’s measured nitrogen level multiplied by 6.25 - it can be manipulated through the addition of any nitrogenous product (i.e. melamine) or inclusion of an overabundance of non-essential amino acids (NEAAs).


Therefore, it is strongly recommended to purchase processed pet food from reputable manufacturers with well-established legislation in manufacturing countries that safeguard the pets and pet – custodians’ interests.

Based on the Association of American Feed Control Officials (AAFCO) Nutrient Profiles-:

CANINE REQUIREMENTS -

1. ADULT DOGS

The minimum crude protein

(in percentage) on a

dry matter basis  (i,e, no moisture included)

2. PUPPIES
The minimum crude protein

(in percentage) on a

dry matter basis  (i,e, no moisture included)

HOW MUCH PROTEIN TO FEED?

FELINE REQUIREMENTS -

1. ADULT CATS

The minimum crude protein

(in percentage) 

on a dry matter basis (i,e, no moisture included)

2. KITTENS
The minimum crude protein

(in percentage)

on a dry matter basis  (i,e, no moisture included)

Many commercial pet foods that do not comply with AAFCO recommendations claim to have already been formulated to contain a higher amount of protein than the AAFCO minimum requirements for pet cats and dogs.

18%

22.5%

26%

30%

The amount of protein fed can vary depending on the health status and condition of the pet in view.

 

Feeding a diet that is higher in protein than the calculated need does not always result in any health benefits or adverse reactions.

For a healthy pet, excess protein is unlikely to be harmful, the extra protein will just be broken down by the body and eliminated in the urine.

The amount of dietary proteins, together with the quality and digestibility of the protein, both play important parts in helping maintain and build muscle sooner, especially in sick and/or elderly pets.

 

Eating more good or high-quality protein can improve the body's maintenance abilities, growth, mobility, enhance satiety, regulate thermogenesis, improve blood glucose regulation, aid in recovery after trauma, diseases, surgery, or prolonged bed rest. 

CASE STUDY

The average minimum protein requirement for a healthy adult cat is 4g/ kg of body weight per day.

 

That is, a 4 kg cat will need a minimum of

16 g of protein per day (providing 64 calories).

 

Can Food A has the following guaranteed analysis:

 

1.    Crude Protein 8% (minimum percentage)
2.   Crude Fat 0.1% (minimum percentage)
3.   Crude Fiber 1% (maximum percentage)
4.   Moisture 89% (maximum percentage)

Dry Food B  has the following guaranteed analysis:

1.    Crude Protein 40% (minimum percentage) 

2.   Crude Fat 18% (minimum percentage)

3.   Crude Fiber 4% (maximum percentage)

4.   Moisture 10% (maximum percentage)

At first glance, you may be tempted to conclude that Dry Food B has a high protein content, is of better value, and will provide more nutrients suited for a cat.

However, to compare the true crude protein percentage between canned food and dry food, the following calculation must be done to remove the moisture content in the formulation.

Remove moisture from Can Food A-:100-89= 11

 

1.    Crude Protein

= (8/11) x 100%  = 72%  (minimum percentage)
2.   Crude Fat

= (0.1/11) x 100%= 0.9% (minimum percentage)
3.   Crude Fiber

= (1/11) x 100% = 9%(maximum percentage)
4.   Moisture

= 89% (maximum percentage)

Remove moisture from Dry Food B-:100-10= 90

1.    Crude Protein

= (40/90) x 100% = 44.45% (minimum percentage) 

2.   Crude Fat

=(18/90)x 100% = 20% (minimum percentage)

3.   Crude Fiber

= (4/90) x 100% = 4.45% (maximum percentage)

4.   Moisture

= 10% (maximum percentage)

Based on this, both diets fulfill AAFCO's protein nutrient requirement for cats.

 

But it becomes obvious that Can Food A has a higher Crude Protein value (72%) and a lower Crude Fat value (0.9%) compared to Dry Food B (44.45% and 20% respectively),    and thus can be given to overweight or elderly cats than require more amino acids and lesser fat in their diet.

Using the same example of a 4kg cat, the estimated Daily Energy Requirement (DER) will be calculated RER multiplied by the neutered/ spayed factor ranging from 1.2 based on the assessed BCS and MCS.

Let us multiply the RER with 1.2:

Daily Energy Requirement (DER)

= Resting Energy Requirement x Midpoint of weight gain factor

= [(4x30) + 70] x 1.2

= 190 x 1.2 

228 Kilocalories per day

Therefore, the cat must consume 228 Kilocalories per day to thrive and maintain its current weight.

The emphasis must be placed on the fact that this equation will only provide us with an “estimated DER value.”

Now, examine the food you have decided to feed - Can Food A:

The total  Metabolisable Energy (ME) of Can Food A is  35.04 kilocalories per can (80g).

 

 

Number of canned food per day

= DER / ME

= 228/35.04

= 6.5 cans per day

 

Therefore, to maintain the weight of the 4 kg cat, we should start by feeding 6.5 cans of the chosen canned food daily to meet the estimated DER for weight gain.

This will be true if you are feeding only Can Food A as the daily diet.

 

This will be considered the starting point only.

 

The pet dog in question should be weighed every 2 weeks to monitor for weight gain and adjustments must made accordingly.

Now, examine the other food you can feed - Dry Food B:

20231202_165448[1]_edited.jpg

If the weight gain Is too slow, the DER should be recalculated.

Daily Energy Requirement (DER)

= Resting Energy Requirement x Highest weight gain factor

= [(14x30) + 70] x 1.8

= 490 x 1.8 

882 Kilocalories per day

Number of canned food per day

= DER / ME

= 882/463

= 1.9 can per day

The food fed per day to the dog thus can range between 1.5 to 1.9 (rounding off to 2 cans) cans of food until the body weight reaches 15.5kg.

Assuming, the 14 kg dog reaches 15.5 kg after 3 months, we will then calculate a maintenance feeding protocol to keep the weight at 15.5kg with the correct muscle and subcutaneous layer distribution by adjusting the DER in the chosen food as follows:

 

Daily Energy Requirement (DER)

= Resting Energy Requirement x Maintenance factor for a neutered adult dog

[(15.5x30) + 70] x 1.6

= 856 kilocalories per day

Number of can food per day

= DER / ME

= 856/463

= 1.85can per day

 

The muscle and subcutaneous layer distribution can be further fine-tuned by altering the protein percentage in the food offered, but we will discuss protein intake and adjustment in this article.

LIFE STAGE/ LIFESTYLE LOGIC

 

If your pet is below 1 year old, please expect that it should have a good layer of blubber – no baby animals should be lean or resemble a supermodel.

 

Growing animals must have adequate nutrition for the growth and development of all vital organ systems, daily basic metabolic expenditure, and a slight excess for just-in-case situations.

Please refer to the recommended life stage/ lifestyle factor (2-3, not for giant breeds like Great Danes) needed to achieve a correct DER for proper growth and development.

 

If your pet is more than 1 year old, please check that the pet has developed or is developing and maintaining a good and strong muscle layer protecting all the vital bone structures.

Most commercial pet food will always state on their generic feeding chart that the recommended feeding amount is meant for an “average adult dogs with normal activity levels.”

 

Please do not assume that the apparent “normal activity levels” is the same for every pet dog or pet cat.

 

A neutered Ragdoll cat will not have the same metabolic rate or activity expenditure as a neutered Bengal cat.

 

You should determine and adjust the calorie requirement based on the pets BCS and MCS and numerical weight changes, at least monthly.

 

If your pet is more than 7 years old, please check if sarcopenia has started, you will then need to reduce the calorie intake and increase the protein intake to maintain the muscle mass, tissue and ligament elasticity that helps hold up the bone structures.

Author Contributions

Dr. Denise Ng BSC BVMS

Conflict of interest

The author declares that there is no conflict of interest.

Funding

The author received no specific grant from any funding agency in the public, commercial or not-for-profit sectors for the preparation of this review article.

Attribution:

1. AAFCO: Consumers; Understanding Pet Food: Calories. www.aafco.org/consumers/understanding-pet-food/calories/. Accessed 27 Oct 2023.

2. AAFCO: Animal Feed Labeling Guideline 2020. www.aafco.org/wp-content/uploads/2023/01/Feed-Labeling-Guide-with-new-Cover.pdf. Accessed 10 Oct 2023.

3. AAFCO: How to understand a dog or cat food label. www.aafco.org/consumers/understanding-pet-food/reading-labels/#adequacy. 

Accessed 10 3 Nov 2023

4. https://www.aafco.org/wp-content/uploads/2023/01/Model_Bills_and_Regulations_Agenda_Midyear_2015_Final_Attachment_A.__Proposed_revisions_to_AAFCO_Nutrient_Profiles_PFC_Final_070214.pdf. Accessed 3 Nov 2023

5. Lisa M. Freeman, DVM, PhD, DACVIM (Nutrition). (28 Dec 2020). What Is Guaranteed about the Guaranteed Analysis?  Accessed 29 Oct 2023.

6. Deborah E. Linder, DVM, MS, DACVIM (Nutrition). (11 Nov 2016). What are these numbers? Nutrition Math 101  Accessed 29 Oct 2023.

7. David Dzanis, DVM, PhD, DACVN. Pet food labels: Cracking the code (Proceedings). www.dvm360.com/view/pet-food-labels-cracking-code-proceedings. Accessed 30 Oct 2023.

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