Livro DRI 2006 (Micronutrientes)

Livro DRI 2006 (Micronutrientes)


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acids, and conjugated linoleic acid.
3 Neither an EAR (and thus 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. A UL was
not set for total fat. AIs for total fat were set for infants aged 0
through 12 months based on observed mean fat intake of
infants who were principally fed human milk.
3 An AMDR has been estimated for total fat at 20\u201335 percent of
energy for adults and children aged 4 and older and 30-40
percent for children ages 1 through 3.
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 139
\u2713 The main food sources of total fat are butter, margarine,
vegetable oils, visible fat on meat and poultry products, whole
milk, egg yolk, nuts, and baked goods.
\u2713 Neither an EAR (and thus RDA) nor an AI was set for trans or
saturated fatty acids because they are not essential and have
no known role in preventing chronic disease.
\u2713 There is a positive linear trend between both trans and
saturated fatty acid intake and LDL cholesterol levels, and thus
increased risk of CHD. A UL was not set for trans or saturated
fatty acids because any incremental increase in intake
increases the risk of CHD.
\u2713 It is recommended that individuals maintain their trans and
saturated fatty acid intakes as low as possible while
consuming a nutritionally adequate diet.
\u2713 Food sources of saturated fatty acids tend to be meats, bakery
items, and full-fat dairy products. Foods that contain trans fatty
acids include traditional stick margarine and vegetable
shortenings that have been partially hydrogenated, with lower
levels in meats and dairy products.
\u2713 Cis monounsaturated fatty acids can be synthesized by the
body and confer no known health benefits. Since they are not
required in the diet, neither an AI nor an RDA was set. There
was insufficient evidence to set a UL.
\u2713 Animal products, primarily meat fat, provide about 50 percent
of dietary cis monounsaturated fatty acids intake.
\u2713 Linoleic and \u3b1-linolenic fatty acids are essential, and therefore
must be obtained from foods. AIs were set based on intake of
healthy individuals. There was insufficient evidence to set a UL
for cis polyunsaturated (n-6 and n-3) fatty acids.
\u2713 Foods rich in n-6 polyunsaturated fatty acids include nuts,
seeds, certain vegetables, and vegetable oils, such as
sunflower, safflower, corn, and soybean oils. Major food
sources of n-3 polyunsaturated fatty acids include certain
vegetable oils (flaxseed, canola, and soybean oils) and
fatty fish.
\u2713 High-fat diets in excess of energy needs can cause obesity.
Several studies have shown associations between high-fat
intakes and an increased risk of CHD, cancer, and insulin
resistance. However, the type of fatty acid consumed is very
important in defining these associations.
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
140 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
CHOLESTEROL
Cholesterol plays an important role in steroid hormone and bile acidbiosynthesis. It also serves as an integral component of cell membranes.Most people absorb between 40 and 60 percent of ingested cholesterol.
Such variability, which is probably due in part to genes, may contribute to
the individual differences that occur in plasma cholesterol response to dietary
cholesterol.
All tissues are capable of synthesizing enough cholesterol to meet their
metabolic and structural needs. Consequently, there is no evidence for a bio-
logical requirement for dietary cholesterol. Neither an Estimated Average Re-
quirement (EAR), and thus a Recommended Dietary Allowance (RDA), nor an
Adequate Intake (AI) was set for cholesterol.
Much evidence indicates a positive linear trend between cholesterol intake
and low density lipoprotein (LDL) cholesterol concentration, and therefore an
increased risk of coronary heart disease (CHD). A Tolerable Upper Intake Level
(UL) was not set for cholesterol because any incremental increase in cholesterol
intake increases CHD risk. It is recommended that people maintain their di-
etary cholesterol intake as low as possible, while consuming a diet that is nutri-
tionally adequate in all required nutrients.
High amounts of cholesterol are found in liver and egg yolk. The main
adverse effect of dietary cholesterol is increased LDL cholesterol concentration,
which could result in an increased risk for CHD.
CHOLESTEROL AND THE BODY
Function
Cholesterol is a sterol that is present in all animal tissues. Tissue cholesterol
occurs primarily as free (unesterified) cholesterol, but is also bound covalently
(via chemical bonds) to fatty acids as cholesterol esters and to certain proteins.
Cholesterol is an integral component of cell membranes and serves as a precur-
sor for hormones such as estrogen, testosterone, and aldosterone, as well as bile
acids.
Absorption, Metabolism, Storage, and Excretion
Cholesterol in the body comes from two sources: endogenous and dietary. All
cells can synthesize sufficient amounts of cholesterol for their metabolic and
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: CHOLESTEROL 141
structural needs. Dietary cholesterol comes from foods of animal origin, such as
eggs, meat, poultry, fish, and dairy products.
Dietary and endogenous cholesterol are absorbed in the proximal jejunum,
primarily by passive diffusion. Cholesterol balance studies show a wide varia-
tion in the efficiency of intestinal cholesterol absorption (from 20 to 80 per-
cent), with most people absorbing between 40 and 60 percent of ingested cho-
lesterol. Such variability, which is probably due in part to genetic factors, may
contribute to the differences seen among individuals in plasma cholesterol re-
sponse to dietary cholesterol. In addition, cholesterol absorption may be re-
duced by decreased intestinal transit time.
In the body, cholesterol can be stored in the liver; secreted into the plasma
in lipoproteins, primarily very low density lipoproteins (VLDL); oxidized and
secreted as bile acids; or directly secreted into the bile. Free and esterified
cholesterols circulate principally in LDL in the blood. The body tightly regu-
lates cholesterol homeostasis by balancing intestinal absorption and endogenous
synthesis with hepatic excretion and bile acids derived from hepatic cholesterol
oxidation. Increased hepatic cholesterol delivery from the diet and other sources
results in a complex mixture of metabolic effects that are generally directed at
maintaining tissue and plasma cholesterol homeostasis. Observational studies
have shown that increased dietary cholesterol intake leads to a net increase in
plasma LDL cholesterol concentrations.
DETERMINING DRIS
Determining Requirements
All tissues are capable of synthesizing enough cholesterol to meet their meta-
bolic and structural needs. Consequently, there is no evidence for a biological
requirement for dietary cholesterol. Neither an Estimated Average Requirement
(EAR), and thus a Recommended Dietary Allowance (RDA), nor an Adequate
Intake (AI) was set for cholesterol. However, it is recommended that people
maintain their dietary cholesterol intake as low as possible, while consuming a
diet nutritionally adequate in all required nutrients.
The UL
The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient
intake that is likely to pose no risk of adverse effects for almost all people. Much
evidence