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.

 

Protein

• 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

 

Carbohydrates

 

• 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).

 

Fat

 

• 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.

 

Vitamins

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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.

 

Water

 

• 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.

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• 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.

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• 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 

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• The effect of diet on Diabetes Mellitus

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• The effect of diet on Inflammatory Bowel Disease