Page 66 - Small Animal Clinical Nutrition 5th Edition

66 Small Animal Clinical Nutrition

RER occur in animals with normal body condition or older glycosidic bonds, whereas sugars in fibers are linked by β-gly-
VetBooks.ir animals that lose weight. cosidic bonds. This small difference is important; mammalian
enzymes can break α-bonds but only microbial enzymes can
break β-bonds (Figure 5-11).
WEIGHT GAIN
Weight gain occurs in growth; the energy requirements dur-
ing growth have been discussed previously. Weight gain that Structure
occurs in nongrowing animals results in changes in energy Simple sugars are divided into subgroups depending on the
requirements needed to maintain the increase in body weight number of carbon atoms they contain. Three-carbon sugars
(Boxes 5-5 and 5-6). Research in people shows that REE (saccharides) are: 1) trioses (C H O ) such as glyceralde-
3 6 3
increases linearly with increases in body weight and gains in hyde, 2) four-carbon sugars are tetroses (C H O ), 3) five-
4 8 4
lean body mass (Saltzman and Roberts, 1995).Theoretical cal- carbon sugars are pentoses (C H O ) such as ribose and
5 10 5
culations of increased energy expenditure due to weight gain xylose, 4) six-carbon sugars are hexoses (C H O ) such as
6 12 6
and actual measurements agree closely and can be described by glucose, galactose and fructose and 5) seven-carbon sugars are
the regression equation REE (kcal/day) = 55.6 + 16.9 x weight called heptoses (C H O ). Only one disaccharide has been
7 14 7
change (kg) (Saltzman and Roberts, 1995). found in mammals (i.e., lactose), whereas the most common
The composition of the weight gain averaged 63% body fat plant disaccharide is sucrose. Many oligosaccharides are com-
and 37% lean tissue in a summary of six studies involving 89 monly found in plants. The trisaccharide raffinose and the
adult people (Saltzman and Roberts, 1995). The additional tetrasaccharide stachyose are the two most common oligosac-
energy needed to support weight gain is mainly due to the charides found in plants (e.g., soybeans and other legume
amount of lean body mass that is gained and the energy seeds, sugar beets, root crops and sugar beet molasses).
required to support the increased protein turnover in the newly Longer chain oligosaccharides can be found in a variety of
deposited protein. plants used as food.
There are no estimates supported by research using dogs and Starch is made up of glucose units in straight chains with
cats to correlate composition of weight gain in adults with α1,4 bonds (amylose) and with α1,6 bonds that form branch-
changes in energy requirements. Therefore, in practice, dogs es (Figure 5-11). Small intestinal digestive enzymes can break
and cats that need to gain weight are usually fed more food, or the α1,4 and α1,6 bonds. Starches in plants are called amy-
a food with a higher energy density, until the desired weight has lopectins whereas animal starch is called glycogen. Plant
been achieved.The new target body weight is then used to cal- starches exist as semicrystalline granules that vary in size,
culate DER, and the pet is fed the amount of food necessary to shape and amount of other compounds (proteins) associated
maintain the new desired body weight. This method is effec- with the granule.
tive, but it is difficult to predict how much of a food increase is The granular structure of starch affects the ease with which
truly needed or to estimate how long it will take for the animal it is digested (Table 5-5). Most starches in cooked and extrud-
to gain the needed weight. Suggested energy calculations for ed pet foods are easily and rapidly digested. Raw or uncooked
weight gain are summarized in Table 5-2. starch is typically digested more slowly than cooked starch.
Some plant starches resist enzymatic digestion in the small
intestine (Englyst and Cummings, 1987) and have been named
CARBOHYDRATES INCLUDING FIBER resistant starch (RS). RS, by definition, is not enzymatically
digested in the small intestine, thus it becomes available for
Simple Carbohydrates and Starches microbial fermentation in the colon.
Definition The amounts of rapidly digestible, slowly digestible and RS
Carbohydrates are composed of carbon, hydrogen and oxygen in foods are highly variable and depend on the starch source,
in the general formula (CH O) (Figure 5-11). Carbohydrates type and extent of processing (BNF, 1990). Table 5-5 shows a
2
n
encompass: 1) simple sugars such as monosaccharides (e.g.,glu- nutritional classification of the types of starch found in foods.
cose) and disaccharides (e.g., sucrose), 2) oligosaccharides
(three to nine sugar units; e.g., raffinose, stachyose) and 3) poly- Function
saccharides (more than nine sugar units). Examples of polysac- The body uses simple carbohydrates and starches in foods as a
charides include starches (amylose, amylopectin, glycogen), source of glucose. As such, they have several major functions.
hemicellulose, cellulose, pectins, gums, etc. First, they provide energy (ATP) via glycolysis and the TCA
In a nutritional sense, polysaccharides, or as they are more cycle. Second, when metabolized for energy to carbon dioxide
commonly known, complex carbohydrates, can be further and water, they are a source of heat for the body. Third, as they
defined based on digestibility (Table 5-4). Complex carbohy- proceed through metabolic pathways, certain products can be
drates that are digested by the animal’s endogenous digestive used as building blocks for other nutrients, such as nonessential
enzymes are designated starches, whereas those polysaccharides amino acids, glycoproteins, glycolipids, lactose, vitamin C, etc.
that are resistant to enzymatic digestion and thus are ferment- Finally, simple carbohydrates and starches in excess of the
ed by intestinal microbes are labeled fibers. Starches and fibers body’s immediate energy needs are stored as glycogen or con-
differ chemically in that sugars in starches are linked with α- verted to fat.