Livro DRI 2006 (Micronutrientes)

Livro DRI 2006 (Micronutrientes)


DisciplinaNutrição e Dietética3.699 materiais55.618 seguidores
Pré-visualização50 páginas
of cholesterol and bile acids, which may result
in reduced blood cholesterol concentrations and a reduced risk of CHD.
Absorption, Metabolism, and Excretion
Once consumed, Dietary Fiber and Functional Fiber pass relatively intact into
the large intestine. Along the gastrointestinal tract, the properties of different
fibers result in varying physiological effects:
Gastric emptying and satiety: Viscous fiber delays gastric emptying, thereby
slowing the process of absorption in the small intestine. This can cause a feeling
of fullness, as well as delayed digestion and absorption of nutrients, including
energy. Delayed gastric emptying may also reduce postprandial blood glucose
concentrations and potentially have a beneficial effect on insulin sensitivity.
Fermentation: Microflora in the colon can ferment fibers to carbon dioxide,
methane, hydrogen, and short-chain fatty acids. Foods rich in hemicellulose
and pectin, such as fruits and vegetables, contain Dietary Fiber that is more
completely fermented than foods rich in celluloses, such as cereals. The con-
sumption of Dietary and certain Functional Fibers, particularly those that are
poorly fermented, is known to improve fecal bulk and laxation and ameliorate
constipation.
Contribution of fiber to energy: When fiber is anaerobically fermented by
micro-flora of the colon, the short-chain fatty acids that are produced are ab-
sorbed as an energy source. Although the exact yield of energy from fiber in
humans remains unclear, current data indicate that the yield is between 1.5
and 2.5 kcal/g.
Physiological effects of isolated and synthetic fibers: Table 2 summarizes the
beneficial physiological effects of certain isolated and synthetic fibers. Note that
the discussion of these potential benefits should not be construed as endorse-
ments of the fibers. For each fiber source listed, evidence relating to one of the
three most commonly accepted benefits of fibers is presented: laxation, nor-
malization of blood lipid levels, and attenuation of blood glucose responses.
DETERMINING DRIS
Determining Requirements
There is no biochemical assay that can be used to measure Dietary Fiber or
Functional Fiber nutritional status. Blood fiber levels cannot be measured be-
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
114 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
TABLE 2 The Physiological Effects of Isolated and Synthetic Fibers
Potential Effect on
Attenuation
Normalization of Blood Other
of Blood Lipid Glucose Physiological
Laxation Levels Responses Effects
Cellulose Increases stool No effect on blood Did not decrease \u2014
weight; may lipid levels or a postprandial
decrease transit slight increase glucose response.
time. in them.
Chitin and There was no Numerous animal No known reports Some animal studies
Chitosan evidence for a studies suggested in humans. have shown that
laxative effect in that chitin and chitosan reduces fat
humans. chitosan may absorption and may
decrease lipid promote weight
absorption. loss. However,
However, this has human studies have
not always been found no effect of
observed in chitosan
controlled human supplementation
studies. More on weight.
research is needed.
Guar Gum Little effect on Numerous studies Viscous fibers, \u2014
fecal bulk or have shown an including guar
laxation. 11\u201316 percent gum, produced
reduction in blood significant
cholesterol levels reductions in
with guar gum glycemic response
supplementation. in 33 of 50 studies.
In addition, guar
gum has been
shown to decrease
triacylglycerol
concentrations and
blood pressure.
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
PART II: FIBER 115
Inulin, A few studies Studies with inulin Some, but not all, Numerous human
Oligofructose, have shown a or oligofructose studies suggest studies show that
and Fructooligo- small increase have provided that inulin and the ingestion of
saccharides in fecal bulk mixed results. fructooligo- fructooligo-
and stool saccharides saccharides
frequency with reduce fasting increases
ingestion of insulin fecal Bifidbacteria.
inulin or concentrations or This bacteria strain
oligofructose. fasting blood has been shown to
glucose. have beneficial
health effects in
animals, but the
potential benefits to
humans are not well
understood.
Oat Products Extracted b- In a large study of Some research \u2014
and bbbbb-Glucans glucans have adults with multiple suggests that oat
minimal effects risk factors for heart bran reduces
on fecal bulk. disease, including postprandial rises
Oat bran high LDL cholesterol in blood glucose
increases stool levels, oat cereal levels.
weight by consumption was
supplying rapidly linked to a dose-
fermented dependent reduction
viscous fiber to in LDL cholesterol.
the colon for Other research also
bacterial growth. suggests that oat
products help lower
LDL cholesterol.
TABLE 2 Continued
Potential Effect on
Attenuation
Normalization of Blood Other
of Blood Lipid Glucose Physiological
Laxation Levels Responses Effects
continued
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
116 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
Pectin A meta-analysis Pectin has been Viscous fibers, \u2014
of about 100 shown to lower including pectin,
studies showed cholesterol to have significantly
that pectin is not varying degrees. reduced glycemic
an important There was some response in 33 of
fecal-bulking evidence that this 50 studies.
agent. effect was due to
increased excretion
of bile acids and
cholesterol.
Polydextrose Polydextrose In one study, \u2014 \u2014
was shown to polydextrose
increase fecal lowered HDL (high
mass and density lipoprotein)
sometimes stool cholesterol levels.
frequency.
Findings on the
effect of
polydextrose on
fecal bacterial
production are
mixed.
Psyllium There is A number of studies When added to a \u2014
extensive have shown that meal, psyllium has
literature on the psyllium lowers been shown to
laxative effect of total and LDL decrease the rise
psyllium, which cholesterol levels of postprandial
is the active via the stimulation glucose levels
ingredient in of bile acid and to reduce the
some over the production. glycemic index
counter of foods.
laxatives.
TABLE 2 Continued
Potential Effect on
Attenuation
Normalization of Blood Other
of Blood Lipid Glucose Physiological
Laxation Levels Responses Effects
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
PART II: FIBER 117
Resistant No evidence to One study showed One animal study \u2014
Dextrins support a that resistant and two human
laxative effect. maltodextrin helps studies suggest
reduce blood that resistant
cholesterol and maltodextrins
triacylglycerol reduce fasting
levels. and postprandial
blood glucose
levels.
Resistant Increased fecal Several animal In one study, \u2014
Starch bulk due to studies have adding resistant
increased starch shown that starch to bread
intake has been resistant starch at various levels
reported. lowers blood was shown to
Because cholesterol and reduce the
resistant starch triacylglycerol glycemic index in
is partly levels. In humans, a dose-dependent
fermented in the resistant starch manner.
colon,