Specifics of Feline Metabolism

3. Specifics of Feline Metabolism

Adaptation to a Carnivorous Diet

The cat is a true carnivore which distinguishes it clearly from the omnivorous dog. The natural diet of wild felids, e.g., mice, contains approximately 70 - 80% water. On a dry matter basis (on DMB), it contains about 55 - 60% of protein, 35% of fat, but less than 10% carbohydrate. This is very different from many commonly used commercial dry cat foods which contain a much higher percentage of carbohydrates, mainly represented by starch from cereals, even if a high digestible dry catfood should not contain more than 40% carbohydrates on DMB. Cats fed a high protein diet (54% on DMB) did not show postprandial hyperglycemia (Martin & Rand, 1999) (see also Figure 4a & Figure 4b), unless relatively high amounts of simple sugars were added (Figure 4b). This may be one of several reasons why diets high in protein, i.e. near-natural diets, have beneficial effects in controlling nutrient metabolism in diabetic cats (see below).

Figure 4a. Lack of postprandial hyperglycemia in cats fed a high protein diet (54% protein and 8% carbohydrate on DMB).

Figure 4b. Influence of the diet on postprandial hyperglycemia in 12 cats.

Intensive gluconeogenesis

In cats, gluconeogenesis from amino acids is not downregulated even if protein intake is deficient (Rogers et al, 1977).

As a direct effect of a low carbohydrate intake under natural feeding conditions, cats have developed a high capacity for intensive gluconeogenesis from glucogenic amino acids. (© Lenfant/RC).

The activity of gluconeogenic enzymes is much higher in cats than in dogs (Washizu et al, 1998; Washizu et al, 1999; Takeguchi et al, 2005). On the other hand, cats seem to be deficient in hepatic glucokinase (GK) function due to low hepatic GK expression or enzymatic activity (Washizu et al, 1999; Schermerhorn, 2005; Tanaka et al, 2005; but see section on pancreatic glucose sensing in cats via GK). However, regulation of GK activity in cats seems to differ from other species because cats have a very low activity in GK regulating protein (Schermerhorn, 2005) which in other species would be associated with high GK activity. The activity of other glycolytic key enzymes, including hexokinase which can perhaps partly compensate for low GK activity, is higher in cats than in dogs (Washizu et al, 1999).