Proteins are one of the molecules that make up living things. They are actually chains of amino acids, held together by peptide bonds. These chains of amino acids fold into three-dimensional shapes. Their final shape determines their function. About half the "dry weight" (not including water) of any animal cell is protein.

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Amino acids are essential for all living cells and are needed:

• to regulate metabolism

• for tissue growth

• to help manufacture energy during periods of low food supply.

 

The proteins that amino acids form make up the structural components of:

• cells

• antibodies

• many hormones.

 

Deficiency of proteins (hence amino acids) have an adverse effect on: 

• organs

• cells

• the immune system

• mucousal function, and

• the permeability of the small intestine.

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There are 22 amino acids, which include:

• alanine

• arginine *

• asparagine

• aspartic acid

• cysteine

• cystine

• glutamine

• glutamic acid

• glycine

• histidine *

• hydroxy praline

• isoleucine *

• leucine * 

• lysine *

• methionine *

• phenylalanine *

• proline

• serine *

• threonine *

• tryptophan *

• tyrosine

• valine

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While all amino acids are important for dogs to thrive, ten are considered essential for dogs (* above). By definition, essential means the body cannot manufacture it. So, they must be provided through the diet.

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The non-essential amino acids can be manufactured by the dog's liver.

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Amino acids:

• make collagen and elastin in cartilage, tendons and ligaments

• make contractile proteins (Actin & myosin) in muscles

• make keratin in skin, hair & nails

• make blood proteins

• supply nitrogen for nitrogen containing compounds, and

• are a source of energy.

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There are three types of essential amino acids:

1. glucogenic - can manufacture glucose

2. ketogenic - can be broken down into ketones or fatty acids (sources of fuel during low energy intake)

3. glucogenic & ketogenic 

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The main amino acids include:

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1. Arganine:

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Function:

• removes ammonia

• builds proteins

• releases hormones (regulates the blood sugar hormone insulin & glucagon)

• cell signals

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Deficiency:

• weight and apatite loss

• ammonia buildup (vomiting and muscle tremors)

• puppies can develop cataracts

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Sources:

• good quantities- fish, meat

• lesser  amounts - mushrooms, spirulina, sprouted beans, legumes

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2. Histidine:

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Function:

• oxygen exchange

• tissue growth and repair

• precursor for histamine (immune function)

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Sources:

• good quantities - meats, soy. fish

• lesser  amounts - nuts, seeds, eggs, legumes

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3. Isoleucine: 

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Function:

• stored in large amounts in the body

• protein formation

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Deficiency: 

• poor apatite and weight loss

• impaired growth

• poor skin and coat

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Sources:

• good quantities - eggs, spirulina, poultry, game meat, fish, pork

• lesser  amounts - legumes

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4. Leucine:  is a ketogenic amino acid

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Function:

• regulates other amino acids

• manufactures proteins

• helps control insulin levels

• growth and repair of bone, skin and muscles

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Deficiency:

• liver disease

• reduced apatite and weight loss

• poor growth

• skin issues

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Sources:

• good quantities - meats, spirulina

• lesser  amounts - quinoa, brown rice, buckwheat

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5. Lysine:  another ketogenic amino acid

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Function:

• found in collagen which supports soft tissue

• regulates cell metabolism

• precursor of carnitine (important role in energy metabolism)

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Deficiency:

• apatite and weight loss

• disruption in arginine absorption (excess lysine causes arginine deficiency)

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Sources:

• good quantities - meat, fish, shellfish

• lesser  amounts - eggs, grains

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6. Methionine:

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Function:

• makes protein

• needed for normal growth

• regulates enzymes

• cell division and growth

• one of the most limiting amino acids

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Deficiency:

• weight loss

• skin issues

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Excess:

• vomiting

• ataxia (lack of muscle control or coordination of voluntary movements)

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Sources:

• good quantities - animal proteins

• lesser  amounts - egg, dairy, legumes

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7. Phenylalanine:

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Function:

• converted to the amino acid tyrosine

• protein structure and normal growth

• regulates hormones and cell reproduction

• affects brain chemicals and hence moods

• involved in pigmentation (dogs with dark coats need more than dogs with light coats)

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Deficiency:

• confusion

• depression

• lack of apatite

• reddening of coat

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Sources:

• good quantities - meats, fish

• lesser  amounts -eggs, milk, legumes, greens

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8. Threonine:

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Function:

• controls protein and enzyme activity

• in heart, skeletal muscle and nervous system

• forms tooth enamel, collagen and elastin

• produces antibodies - involved in immune function

• precursor for isoleucine

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Deficiency:

• mood disorders

• lameness

• neurological issues in growing animals

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Sources:

• good quantities - meat, eggs, liver fish

• lesser  amounts - legumes, seeds, nuts

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9. Tryptophan:

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Function:

• growth

• nitrogen balance

• produces vitamin B3 (niacin)

• produces serotonin (neurotransmitter)

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Deficiency:

• aggressive behaviour

• glucose can limit its absorption

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Source:

• good quantities - dairy proteins, meats

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10. Valine:

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Function:

• muscle metabolism

• tissue repair

• energy source

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Can be used to treat liver and gall bladder disease.

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Sources:

• good quantities - milk, muscle meats from ruminants, poultry, pork, fish, seeds, nuts

• lesser  amounts - legumes, mushrooms, wholegrains

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11. Taurine:  is essential for cats (dogs can make their own)

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Function:

• dogs manufacture it from cysteine and methionine

• not a true amino acid (doesn't make protein)

• brain, eye and heart function

• healthy blood

• regulates immune system and calcium levels

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Deficiency:

• reproductive failure

• dilated cardiomyopathy  (heart condition)

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Sources:

• highest quantities - heart and brain

• good quantities - poultry, fish, liver

• lesser  amounts - eggs, milk, meat from hooved animals

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Taurine is virtually absent in most plant proteins, therefor vegetarian and vegan diets will cause taurine deficiency in dogs unless synthetic supplements are added to the diet.

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Cooking and processing foods also reduces taurine content.

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12. Glutamine and Glutamate:

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*** Can be conditionally essential in dogs who are sick, undergoing chemotherapy, have diarrhoea and in low birth weight puppies.

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Function:

• preferred mucousal lining in the small intestine

• unstable

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Deficiency:

• linked to leaky gut

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Sources:

• good quantities -bone broth, meat, raw dairy, spirulina, red cabbage, asparagus, broccoli

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Signs of General Protein Deficiency:

• reduced growth rate and milk production

• anorexia

• anaemia

• poor coat

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A Final Word on Proteins:

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A complete protein includes all 10 essential amino acids. Meats are generally complete proteins, whereas plants aren't.

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An ideal protein food source would contain all the essential amino acids and carry them in the right amounts. It is said to have a high biological value. If a protein does not carry all 10 essential amino acids in appropriate amounts it is said to have a low biological value.

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Some examples of biological values:

• Egg   100

• Fish    76

• Beef   75

• Tofu   64

• What flour   41

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But ..... fish is higher in tryptophan than other animal proteins.

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It's important to remember that the biological value is only the potential quality. The actual quality of proteins depends on a dog's ability to digest the food in the diet. Components in a diet do not act in isolation. Any nutrient may positively or negatively impact on the digestion and absorption of other nutrients.

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