Page 72 - Small Animal Clinical Nutrition 5th Edition

72 Small Animal Clinical Nutrition

Table 5-6. Sources of dietary carbohydrates. dogs and cats. Most starches from grains are easily digested in
VetBooks.ir Carbohydrate Sources the small intestine, when fed uncooked (raw) or cooked to dogs
and cats (Meyer and Kienzle, 1991; Gross et al, 1998; Walker
Starchy plants; grains; used as
Amylopectin (plant starch)
thickener in processed foods
Amylose (plant starch) Starchy plants; grains et al, 1994). Potato starch is an exception. Raw potato starch is
contained in granules that have a crystalline structure that
Carrageenan Red seaweed; used in candies and
some processed foods resists digestion by people, dogs and cats (Meyer and Kienzle,
Cellulose Substituent of plant cell walls; major 1991; Englyst and Cummings, 1987a). Freshly cooked potato
component of wheat bran starch, however, is highly digestible. A study showed that rap-
Corn syrup Used in processed foods
Dextrins Used in processed foods idly digestible starch increased from 24 to 65% when extruded
D-Fructose Fruits; traces in most plant foods; (Murray, 2001). However, starch begins to recrystallize when
honey; maple sugar cooled or dried. In vitro digestion studies and studies in people
D-Galactose Component of lactose; produced
during digestion show that up to 13% of the recrystallized potato starch resists
D-Glucose (dextrose) Fruits; traces in most plant foods; digestion by pancreatic amylase and thus will be fermented in
honey; maple sugar the colon (Englyst and Cummings, 1987a; Cummings and
Glycogen (animal starch) Liver; muscle
Hemicellulose Substituent of plant cell walls Englyst, 1995).
High-fructose corn syrup Used in processed foods RS in cereal grains (rice, barley, wheat, sorghum and corn)
Lactose (milk sugar) Milk; dairy products and potato flour converted to rapidly digestible forms with low
Lignin Substituent of plant cell walls
Maltose Sprouted grain; produced during or high temperature extrusion (Murray et al, 2001; Spears and
digestion of starches Fahey, 2004). Bacteria normally present in the small intestine of
Pectins Fruits dogs and cats are able to use these starches; up to 39% of their
Raffinose, stachyose,
verbacose Plant “antifreeze” organic matter disappears after five hours of fermentation
Sucrose Cane sugar; beet sugar; fruits; (Murray et al, 2001). An in vitro study showed that the RS con-
maple sugar centrations of selected feed ingredients corresponded inversely
to their ileal digestibility. For example legumes (various beans
and peas) with an average of 25% RS had an ileal starch
produce only 5% of the pancreatic amylase that dogs produce digestibility of 21%, whereas cereal grains had an average of
(Kienzle, 1993). Unlike dogs, cats lack hepatic glucokinase 15% RS and flours with 3% RS had ileal starch digestibilities of
activity, which limits their ability to metabolize large amounts 60 and 65% respectively (Bednar, 2001). However, the RS frac-
of simple carbohydrates (Kienzle, 1993b; McDonald et al, tion is fermented in the large intestine, contributing to its func-
1984). Glucokinase is responsible for phosphorylating glucose tional properties as a fiber. Fermentation of RS in the colon
to G-6-P in the pathway of glucose oxidation. Feline liver is produces butyrate, which is important for the health of colono-
also thought to lack fructokinase (McDonald et al, 1984). cytes. Some legumes (e.g., soybeans) contain significant quan-
The metabolic differences between cats and dogs support tities of raffinose and stachyose, which can be digested by gut
the classification of cats as strict carnivores, adapted to a low- microflora but not by canine and feline digestive enzymes.
carbohydrate diet, and dogs as omnivores. If large amounts of These sugars allegedly cause digestive abnormalities (e.g., flat-
carbohydrates are fed to cats (e.g., more than 40% of the ulence) due to the gaseous waste products produced by bacter-
food’s DM), signs of maldigestion occur (e.g., diarrhea, bloat- ial fermentation.
ing and gas) (Meyer and Kienzle, 1991) and adverse metabol- Sugar is sometimes added to enhance palatability of foods for
ic effects can occur (e.g., hyperglycemia and excretion of sig- dogs. Commercial semi-moist cat foods use mono- and disac-
nificant amounts of glucose in urine). Despite the limitations charides as functional ingredients to achieve texture and moist-
of digestive capacity and metabolism, the starch levels found ness and to prevent spoilage. Pet food with gravies and sauces
in commercial cat foods (up to 35% of the food’s DM) are may contain dextrins, corn syrup and other starches for texture
well tolerated. There are also differences among carbohydrate and appearance. Sucrose does not enhance palatability of foods
sources and their effects on blood glucose due to the glycemic for cats because cats have few sucrose-sensitive taste buds
index of the specific carbohydrate source. Of the cereal grains, (NRC, 2006; Boudreau and White, 1978). A dog’s ability to
in cats, rice has the greatest effect on postprandial blood glu- taste sweetness is different from a person’s because of differ-
cose levels compared to corn, barley and sorghum (Bouchard ences in the number and type of sweetness receptors on taste
and Sunvold, 2000). buds (Boudreau and White, 1978; Boudreau, 1989).Therefore,
the sweetness rankings of different sugars developed for people
Sources are not applicable to cats and dogs. Unlike in people and other
Starches are the primary carbohydrates found in corn, wheat, primates, dietary sugars do not present a risk for dental caries
rice, barley, oats and potatoes (Table 5-6). Meat is a poor car- in dogs and cats (Chapter 47).
bohydrate source. Commercial extruded pet foods use starches
in grains to provide structure, texture and form to extruded kib- Fiber
bles. In addition, the extrusion process gelatinizes starch, which Definition
makes it easily and rapidly digested in the small intestine of Fiber refers to a multitude of compounds categorized as com-