Livro DRI 2006 (Micronutrientes)

Livro DRI 2006 (Micronutrientes)


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cleared by
the liver. Oxidation of saturated fatty acids is similar to oxidation of other types
of fatty acids (see \u201cTotal Fat\u201d above).
A unique feature of saturated fatty acids is that they suppress expression of
LDL receptors, thus raising blood LDL cholesterol levels. Like other fatty acids,
saturated fatty acids tend to be completely oxidized to carbon dioxide and wa-
ter. Saturated fatty acids also increase HDL cholesterol.
CIS MONOUNSATURATED FATTY ACIDS
Absorption of cis monounsaturated fatty acids is in excess of 90 percent (based
on oleic acid data) in adults and infants, and the pathways of digestion, absorp-
tion, metabolism, and excretion are similar to those of other fatty acids (see
\u201cTotal Fat\u201d above).
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PART II: DIETARY FAT 129
CIS-POLYUNSATURATED FATTY ACIDS
\u2022 n-6 polyunsaturated fatty acids: Digestion and absorption of n-6 fatty ac-
ids is efficient and occurs via the same pathways as those of other long-
chain fatty acids (see \u201cTotal Fat\u201d above). The parent fatty acid of the n-6
fatty acids series is linoleic acid. Humans can desaturate and elongate
linoleic acid to form arachidonic acid. Arachidonic acid is the precursor
to a number of eicosanoids (e.g., prostaglandins, thromboxanes, and
leukotrienes) that are involved in platelet aggregation, hemodynamics,
and coronary vascular tone. The n-6 fatty acids are almost completely
absorbed and are either incorporated into tissue lipids, used in eicosanoid
synthesis, or oxidized to carbon dioxide and water. Small amounts are
lost via the sloughing of skin and other epithelial cells.
\u2022 n-3 polyunsaturated fatty acids: Digestion and absorption is similar to
that of other long-chain fatty acids (see \u201cTotal Fat\u201d above). The body
cannot synthesize a-linolenic acid, the parent fatty acid of the n-3 se-
ries, and thus requires a dietary source of it. a-Linolenic acid is not
known to have any specific functions other than to serve as a precursor
for synthesis of eicosapentaenoic acid (EPA) and docosahexaenoic acid
(DHA). The n-3 fatty acids are almost completely absorbed and are ei-
ther incorporated into tissue lipids, used in eicosanoid synthesis, or
oxidized to carbon dioxide and water. Small amounts are lost via slough-
ing of skin and other epithelial cells.
TRANS FATTY ACIDS
As with other fatty acids, absorption is about 95 percent. Trans fatty acids are
transported similarly to other dietary fatty acids and are distributed within the
cholesteryl ester, triacylglycerol, and phospholipid fractions of lipoprotein. Avail-
able animal and human data indicate that the trans fatty acid content of tissues
(except the brain) reflects diet content and that selective accumulation does not
occur. Trans fatty acids are completely catabolized to carbon dioxide and water.
DETERMINING DRIS
Determining Requirements
TOTAL FAT
Neither an EAR (and thus an RDA) nor an AI was set for total fat for individuals
aged 1 year and older because data were insufficient to determine an intake
level at which risk of inadequacy or prevention of chronic disease occurs. How-
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
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130 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
ever, because of the importance of fat to provide the energy needed for growth,
AIs were set for infants aged 0 through 12 months. These AIs were based on the
observed mean fat intake of infants who were principally fed human milk (0\u20136
months) and human milk and complementary foods (7\u201312 months).
SATURATED FATTY ACIDS
Neither an EAR (and thus an RDA) nor an RDA was set for saturated fatty acids
because they are not essential and have no known role in preventing chronic
disease.
CIS MONOUNSATURATED FATTY ACIDS
Cis monounsaturated fatty acids (n-9) confer no known independent health
benefits. Since these fatty acids are not required in the diet, neither an EAR (and
thus an RDA) nor an AI was set.
CIS POLYUNSATURATED FATTY ACIDS
\u2022 n-6 polyunsaturated fatty acids: In the absence of adequate information
on the amount of linoleic acid required to correct the symptoms of an n-
6 polyunsaturated fatty acid deficiency, an EAR (and hence an RDA)
could not be established. The AIs for linoleic acid are based on the me-
dian intake of linoleic acid by different life stage and gender groups in
the United States, where the presence of n-6 polyunsaturated fatty acid
deficiency is basically nonexistent in healthy individuals.
\u2022 n-3 polyunsaturated fatty acids: Because of the lack of evidence for deter-
mining a requirement in healthy individuals, an EAR (and thus an RDA)
could not be established. The AIs for a-linolenic acid are based on the
median intakes of a-linolenic acid in the United States where the pres-
ence of n-3 polyunsaturated fatty acid deficiency is basically nonexist-
ent in healthy individuals.
TRANS FATTY ACIDS
Trans fatty acids confer no known health benefits. They are chemically classi-
fied as unsaturated fatty acids, but behave more like saturated fatty acids in the
body. Therefore, no EAR (and thus RDA) or AI was set.
CONJUGATED LINOLEIC ACID
There are no known requirements for conjugated linoleic acid (CLA) in the
body. Therefore, no EAR (and thus RDA) or AI was set.
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: DIETARY FAT 131
Criteria for Determining Fat Requirements,
by Life Stage Group
TOTAL FAT
Life stage groupa Criterion
0 through 6 mo Average consumption of total fat from human milk
7 through 12 mo Average consumption of total fat from human milk and
complementary foods
LINOLEIC ACID
Life stage group Criterion
0 through 6 mo Average consumption of total n-6 fatty acids from human milk
7 through 12 mo Average consumption of total n-6 fatty acids from human milk
and complementary foods
1 through 18 y Median intake from CSFIIb
19 through 50 y Median intake from CSFII for 19 to 30 y group
51 y and through 70 y Median intake from CSFII
> 70 y Median intake from CSFII for 51 through 70 y group
Pregnancy Median intake from CSFII for all pregnant women
Lactation Median intake from CSFII for all lactating women
ALPHA-LINOLENIC ACID
Life stage group Criterion
0 through 6 mo Average consumption of total n-3 fatty acids from human milk
7 through 12 mo Average consumption of total n-3 fatty acids from human milk
and complementary foods
1 through 18 y Median intake from CSFIIb
19 y and older Median intake from CSFII for all adult age groups
Pregnancy Median intake from CSFII for all pregnant women
Lactation Median intake from CSFII for all lactating women
a A DRI value for total fat was not set for any life stage group other than infants.
b Continuing Survey of Food Intake by Individuals (1994\u20131996, 1998).
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
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132 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
The AMDR
An AMDR has been estimated for total fat at 20\u201335 percent of energy for adults
and children aged 4 and older and 30\u201340 percent for children ages 1 through
3. The AMDRs for n-6 polyunsaturated fatty acids (linoleic acid) and n-3 poly-
unsaturated fatty acids (a-linolenic acid) are 5\u201310 percent and 0.6\u20131.2 per-
cent, respectively (see Part II, \u201cMacronutrients, Healthful Diets, and Physical
Activity\u201d).
The UL
TOTAL FAT
The Tolerable Upper Intake Level (UL) is