Livro DRI 2006 (Micronutrientes)

Livro DRI 2006 (Micronutrientes)


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the highest level of daily nutrient
intake that is likely to pose no risk of adverse effects for almost all people. Since
there is no defined intake level of total fat at which an adverse effect occurs, a
UL was not set for total fat.
SATURATED FATTY ACIDS AND TRANS FATTY ACIDS
There is a positive linear trend between saturated fatty acid intake and total and
LDL cholesterol levels and a positive linear trend between trans fatty acid and LDL
cholesterol concentration. Any incremental increases in saturated and trans fatty
acid intakes increase CHD risk, therefore a UL was not set for saturated or trans
fatty acids. It is neither possible nor advisable to achieve zero percent of energy
from saturated fatty acids or trans fatty acids in typical diets, since this would
require extraordinary dietary changes that may lead to inadequate protein and
micronutrient intake, as well as other undesirable effects. It is recommended
that individuals maintain their saturated and trans fatty acid consumption as
low as possible while following a nutritionally adequate diet.
CIS MONOUNSATURATED AND CIS POLYUNSATURATED FATTY ACIDS
Evidence was insufficient to set a UL for cis monounsaturated fatty acids, and
cis polyunsaturated (n-6 and n-3) fatty acids.
DIETARY SOURCES
Foods
Dietary fat intake is primarily (98 percent) in the form of triacylglycerols and is
derived from both animal- and plant-based products. The principal foods that
contribute to fat intake are butter, margarine, vegetable oils, visible fat on meat
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
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PART II: DIETARY FAT 133
and poultry products, whole milk, egg yolk, nuts, and baked goods, such as
cookies, doughnuts, and cakes.
In general, animal fats have higher melting points and are solid at room
temperature, which is a reflection of their high content of saturated fatty acids.
Plant fats (oils) tend to have lower melting points and are liquid at room tem-
perature because of their high content of unsaturated fatty acids. Exceptions to
this rule are some tropical oils (e.g., coconut oil and palm kernel oil), which are
high in saturated fat and solid at room temperature.
Trans fatty acids have physical properties that generally resemble saturated
fatty acids, and their presence tends to harden fats. Food sources for the various
fatty acids that are typically consumed in North American diets are listed in
Table 4.
Dietary Supplements
This information was not provided at the time the DRI values for total fat and
fatty acids were set.
INADEQUATE INTAKE AND DEFICIENCY
Total Fat
Inadequate intake of dietary fat may result in impaired growth and an increased
risk of chronic disease. If fat intake, along with carbohydrate and protein in-
take, is too low to meet energy needs, an individual will be in negative energy
balance. Depending on the severity and duration of the deficit, this may lead to
malnutrition or starvation.
If the diet contains adequate energy, carbohydrate can replace fat as an
energy source. However, fat restriction is of particular concern during infancy,
childhood, and pregnancy, during which there are relatively high energy re-
quirements for both energy expenditure and fetal development.
Imbalanced intake can also be of concern. Compared with higher fat diets,
low-fat and high-carbohydrate diets may alter metabolism in a way that in-
creases the risk of chronic diseases, such as coronary heart disease and diabetes.
These changes include a reduction in high density lipoprotein (HDL) choles-
terol concentration, an increase in serum triacylglycerol concentration, and higher
responses in glucose and insulin concentrations following food consumption.
This metabolic pattern has been associated with an increased risk of CHD and
Type II diabetes, although strong evidence does not exist that low-fat diets actu-
ally predispose an individual to either CHD or diabetes.
Some populations that consume low-fat diets, and in which habitual en-
ergy intake is relatively high, have a low prevalence of these chronic diseases.
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
134 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
TABLE 4 Commonly Consumed Food Sources of Fatty Acids
Fatty Acid Food Sources
Saturated fatty acids Sources tend to be animal-based foods, including
whole milk, cream, butter, cheese, and fatty meats
such as pork and beef. Coconut, palm, and palm
kernel oils also contain relatively high amounts of
saturated fatty acids. Saturated fatty acids
provide approximately 20\u201325 percent of energy in
human milk.
Cis monounsaturated fatty acids Animal products, primarily meat fat, provide about
50 percent of monounsaturated fatty acids in a
typical North American diet. Oils that contain
monounsaturated fatty acids include canola and
olive oil. Monounsaturated fatty acids provide
approximately 20 percent of energy in human
milk.
Cis polyunsaturated fatty acids:
n-6 polyunsaturated fatty acids Nuts, seeds, and vegetable oils such as
sunflower, safflower, corn, and soybean oils.
g-Linolenic acid is found in black currant seed oil
and evening primrose oil. Arachidonic acid is
found in small amounts in meat, poultry, and
eggs.
n-3 polyunsaturated fatty acids Major sources include certain vegetable oils and
fish. Flaxseed, canola, and soybean contain high
amounts of a-linolenic acid. Fatty fish are major
dietary sources of EPA and DHA.
Trans fatty acids Traditional stick margarine and vegetable
shortenings subjected to partial hydrogenation,
milk, butter, and meats. Pastries, fried foods,
doughnuts, and french fries are also contributors
of trans fatty acid intake. Human milk contains
approximately 1\u20135 percent of total energy as trans
fatty acids and, similarly, infant formulas contain
approximately 1\u20133 percent.
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 135
Similarly, populations that consume high-fat diets (i.e., \u2265 40 percent of energy)
and experience a low prevalence of chronic diseases often include people who
engage in heavy physical labor, are lean, and have a low family history of chronic
diseases.
Conversely, in sedentary populations, such as those in the United States
and Canada where overweight and obesity are common, high-carbohydrate,
low-fat diets induce changes in lipoprotein and glucose/insulin metabolism in
ways that could raise the risk for chronic diseases. Available prospective studies
have not concluded whether high-carbohydrate, low-fat diets present a health
risk in the North American population.
n-6 Polyunsaturated Fatty Acids
Because adipose tissue lipids in free-living healthy adults contain about 10 per-
cent of total fatty acids as linoleic acid, the biochemical and clinical signs of
essential fatty acid deficiency do not appear during dietary fat restriction or
malabsorption when they are accompanied by an energy deficit. In this situa-
tion, the release of linoleic acid and small amounts of arachidonic acid from
adipose tissue reserves may prevent the development of essential fatty acid de-
ficiency. However, during total parenteral nutrition (TPN) with dextrose solu-
tions, insulin concentrations are high and mobilization of adipose tissue is pre-
vented. This results in the characteristic signs of essential fatty acid deficiency.
When n-6 fatty acid intake is inadequate or absorption is impaired, tissue
concentrations of arachidonic acid decrease, inhibition of