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Review Articles About Diets and Nutrition in Dogs and Cats

The Ins and Outs of Dietary Protein and Dogs

Laflamme DP 2008, ‘Pet food safety: dietary protein’, Topics in Companion Animal Medicine, vol 23, no. 3, pp. 154-7.


This article reviews the evidence surrounding the risks posed by insufficient or excessive dietary protein. Dietary protein is required to provide essential amino acids and replenish protein reserves. When intake is deficient, protein turnover slows and lean body mass is gradually depleted. These changes lead to increased morbidity and mortality.


While severe protein deficiency typically results in poor food intake and weight loss, subclinical protein deficiency in dogs can result in increased or stable body weight but with an increased proportion of body fat and reduced lean body mass.


What is minimum protein amount needed by dogs?


  • In a classic study in young and old beagles, dogs of all ages needed about three times more protein to maintain protein turnover, compared with the amount needed to maintain nitrogen balance.

    • (Wannemacher RW, McCoy JR 1966, ‘Determination of optimal dietary protein requirements of young and old dogs’, Journal of Nutrition, vol. 88, pp. 66-74).


  • The minimum amount of protein needed by old dogs (about 4 g/kg body weight) is about 50% greater than for young dog


  • Adult cats need more than three times as much protein (about 5.2 g/kg body weight) to maintain lean body mass, compared with that needed simply to maintain nitrogen balance


Can there be too much protein in the diet?  


The ability of excess dietary protein to induce renal pathology was studied in both dogs with chronic kidney failure and older dogs without kidney failure.


  • One study compared four carefully controlled diets.  The results showed that protein had no adverse effects, even in dogs with kidney failure, although phosphorus restriction did protect against worsening kidney damage.

    • Finco DR, Brown SA, Crowell WA, et al 1992, ‘Effects of dietary phosphorus and protein in dogs with chronic renal failure’, Am J Vet Res, vol.53, pp. 2264-2271

  •  Two other studies evaluated older (age 6 to 8 years at start of study), uninephrectomized dogs that were fed either dry diets containing 18 or 34% protein or canned diets containing 22 or 36% protein, on a dry matter basis, for 4 years. No adverse effects from dietary protein were observed in either study. On the contrary, in one of these studies, mortality was slightly higher in dogs fed the lower protein diet.

    • Finco DR, Brown SA, Crowell WA, et al 1994, ‘Effects of aging and dietary protein intake on uninephrectomized geriatric dogs’, Am J Vet Res, vol. 55, pp. 1282-1290

    • Churchill J, Polzin D, Osborne CT, et al 1997, ‘Influence of diet on morbidity and mortality in geriatric uninephrectomized dogs’, Proceedings ACVIM, vol. 675.


  • Study - Lees GE, Brown SA, Elliott J, et al 2005, ‘Assessment and management of proteinuria in dogs and cats’, 2004 ACVIM Forum consensus statement (small animal). J Vet Intern Med, vol. 19, pp 377- 385.


  • These studies showed that protein consistent with complete and balanced nutrition has no adverse effects on the kidneys of healthy senior dogs.  However, phosphorus- and protein-restricted diets are clinically beneficial in dogs with existing chronic kidney failure.


Protein for Senior Dogs


Protein restriction for healthy older dogs is not only unnecessary, it can be detrimental. Protein requirements actually increase by about 50% in older dogs, while their energy requirements tend to decrease. When insufficient protein is provided, it can aggravate the age-associated loss of lean body mass and may contribute to earlier mortality. Older dogs should receive at least 25% of their calories from protein, typically provided by diets containing at least 7 g protein/100 Kcal ME.

Cats as Obligate Carnivores and Diet

Zoran, DL 2002, ‘The carnivore connection to nutrition in cats’, Journal of the American Veterinary Medical Association, vol. 221, no. 11, pp. 1559-67.


The review explains what it means metabolically and nutritionally to be an obligate carnivore.


Cats are obligate carnivores that rely on nutrients in animal tissues to meet their specific and unique nutritional requirements.


In their natural habitat, cats consume prey high in protein with moderate amounts of fat and minimal amounts of carbohydrates.  They are metabolically adapted for higher metabolism of proteins and lower utilisation of starch than dogs or omnivores.   Cats can use carbohydrates as a source of metabolic energy, they have limited ability to spare protein utilisation by using carbohydrates instead. 


In spite of this, commercial diets are formulated with a mixture of animal and plant derived nutrients, most commonly in dry kibble form that requires carbohydrates for the expansion and cooking process.



  • Cats are metabolically adapted to preferentially use protein and fat as energy sources.

  • This evolutionary difference in energy metabolism mandates cats to use protein for maintenance of blood glucose concentrations even when sources of protein in the diet are limiting.

  • Adult cats require 2 to 3 times more protein in their diet than adults of omnivorous species.


  • Cats have an increased need for dispensable protein

Cat nutrition studies show that cats continue to use protein (eg, dispensable nitrogen in the form of gluconeogenic amino acids) for production of energy and in other metabolic pathways (eg. urea cycle), even in the face of low availability of proteins.


  • cats also have a need for increased amounts of specific amino acids in their diet:  taurine, arginine, methionine, and cysteine.  Cats neither have the ability to synthesize these amino acids, nor are the amino acids conserved in their bodies. In fact, utilization of these amino acids (taurine, arginine, methionine, and cysteine) is higher in cats than in dogs or other animals.  It is likely that they have not developed mechanisms to conserve them due to the abundance available in their natural diet




  • Cats lack salivary amylase, the enzyme responsible for initiating carbohydrate digestion

  • Cats have low activities of intestinal and pancreatic amylase and reduced activities of intestinal disaccharides that break down carbohydrates in the small intestines.


  • Cats can use starch efficiently BUT as carnivores, high amounts of carbohydrates in the diet may have negative effects on their health


  • decrease protein digestibility in cats


  • cause a reduction in faecal pH in cats (due to incomplete carbohydrate fermentation in the small intestine that results in increased microbial fermentation in the colon and increased production of organic acids).


Hepatic function


  • The liver of the cat has several distinct features that influence disaccharide metabolism:

    • Cats have minimal function of hepatic glucokinase, and the activity is not adaptive (ie cannot be upregulated with the diet contains large amounts of carbohydrates)

    • Cats have minimal activity of hepatic glycogen synthetase (the enzyme responsible for converting glucose to glycogen for storage in the liver).

    • Cats have limited ability to rapidly minimise hyperglycaemia from a large dietary glucose load.

    • The liver in cats does not contain fructokinase, an enzyme necessary for metabolism of simple sugars.

    • Cats are not attracted to foods with a sweet taste.  Cats prefer foods flavoured with animal products (eg fats, meats).




  • Meat based diets supply essential fatty acids to cats, including linoleic, linolenic, arachidonic acid, and some eicosotrienoic acid. 

  • Unlike other animals, cats lack adequate hepatic alpha-6-desaturase activity and other hepatic desaturases, all of which are required for syntheiss of arachidonic acid and eicosapentaenote and docosahexaenoate.

  • Cats do not have the enzymatic machinery to synthesise derivatives of arachidonic acid.



The vitamin needs of cats are unique:

  • cats require increased amounts of dietary water soluble B vitamins  including thiamine, niacin, pyridoxine (B6) and cobalamin (B12). Pyridoxine is especially important as it is an essential co-factor in all transaminase reactions , which are constantly active in cats due to their reliance of protein for energy as well as building and synthetic functions.  Since most water soluble B vitamins are not stored, except cobalamin, which is stored in the liver, a continual dietary source is required.

  • Cats cannot convert beta-carotene to retinol, the active form of vitamin A, thus the biologically active form must be obtained from the diet – from animal tissue.

  • Cats lack the enzyme to allow dermal synthesis of Vitamin D. Vitamin D is found in high levels in fat and liver tissue – thus needs are normally met from the natural diet.




  • Cats have a less sensitive response to thirst and dehydration than dogs and other omnivores. This reflects their development as desert animals and as strict carnivores, which obtain most of their water requirements from their prey.

  • In older cats which produce urine with a lower SG, an increase in water consumption is very important to prevent dehydration and the development of a pre-renal azotaemia


The effect of diet on obesity in cats


  • Cats housed exclusively indoors and consuming energy-dense, high-starch, dry foods are provided with more energy than they can effectively use.  Any dietary carbohydrates not used for energy is converted and store as fats.


  • Diets that are severely restricted for energy (eg traditional low fat, high fibre, weight loss diets) may result in weight loss, but it is often to the detriment of lean body mass.


  • In a study by Nguyen et al. (2001), weight reduction in cats on a high protein, low carbohydrate diet was compared with that for cats fed a commercial hypoenergetic diet.  Cats in both groups lost weight, but cats consuming the high protein low carb diet maintained lean body mass during weight loss.

    • Nguyen P, Martin L, Siliart B et al 2001, Weight loss in obese cats: evaluation of a high protein diet’, in Proceedings.  Waltham International Symposium on Small Animal Nutrition vol 28.


  • The effect of diet on Hepatic Lipidosis 

  • The effect of diet on Diabetes Mellitus

  • The effect of diet on Inflammatory Bowel Disease

Fougere, B 2014, ‘Raw Food, Wholefood and Commercial Diets – Where’s The Evidence?’, American Holistic Veterinary Medical Association Journal, vol. 36, pp 8-15.


Literature review + opinion article from a leading integrative veterinarian, founder of College of Integrative Veterinary Therapies.

Addresses issues of:

  • Food safety – addresses the perception that commercial diets are inherently safer than raw food/ whole food/ natural food for dogs and cats

  • Focusing on manufacturing in the US, the article looks at the risk of bacterial contamination, or contamination by other things such as heavy metal, Toxoplasma or other pathogens.

  • Nutritional deficiencies from feeding unbalanced natural diets and other commercial pet foods from improper storage

  • Link between processed foods and poor health such as obesity, oxidative stress and inflammation.

  • Recommendations for the healthy preparation of homemade diets for pets.

  • The underlying reasons why home natural diets are considered to be beneficial include

    • the high levels of antioxidants, phytochemicals and bioavailable nutrition,

    • the lower caloric density (especially when compared to dry food), &

    • the absence of unnatural additives and by-products associated with processing which may be detrimental to health. 

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