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Cholesterol
comes from two sources. It's produced in your body, mostly in the liver (about
1,000 milligrams a day). And it's found in foods that come from animals, such
as meats, poultry, fish, seafood and dairy products.
The
American Heart Association recom-mends that your average daily intake of dietary
cholesterol should be less than 300 milligrams.
Remember, it is found only in foods from animals. Al-though it's not the same
as a saturated fatty acid, dietary cholesterol can also raise your blood cholesterol
level.
You need cholesterol for your body to function normally, but your body makes enough
so that you don't need to get more from the foods you eat.
Cholesterol
Cholesterol produced in you body is a soft, waxy substance found among the lipids
(fats) in the bloodstream and in all your body's cells. It's an important part
of a healthy body because it's used to form cell membranes, some hormones and
other needed tissues. But a high level of cholesterol in the blood - hypercholesterolemia
- is a major risk factor for coronary heart disease, which causes heart attacks.
Cholesterol and other fats can't dissolve in the blood. They have to be transported
to and from the cells by special carriers of lipids and proteins called lipoproteins.
There are several kinds, but the ones to be most concerned about are low density
lipoprotein (LDL) and high density lipoprotein (HDL).
Dietary Cholesterol
Dietary cholesterol is found in meat, poultry, seafood and dairy products. Foods
from plants - such as fruits, vegetables, vegetable oils, grains, cereals, nuts
and seeds - don't contain cholesterol. Egg yolks and organ meats are high in cholesterol.
Shrimp and crayfish are somewhat high in cholesterol. Chicken, turkey and fish
contain about the same amount of cholesterol as do lean beef, lamb and pork.
(LDL's)
Low Density Lipoproteins
Low density lipoprotein is the major cholesterol
carrier in the blood. When a person has too much LDL cholesterol circulating in
the blood, it can slowly build up within the walls of the arteries feeding the
heart and brain. Together with other substances it can form plaque, a thick, hard
deposit that can clog those arteries. This condition is known as atherosclerosis.
The formation of a clot (or thrombus) in the region of this plaque can block the
flow of blood to part of the heart muscle and cause a heart attack. If a clot
blocks the flow of blood to part of the brain, the result is a stroke. A high
level of LDL cholesterol reflects an increased risk of heart disease. That is
why LDL cholesterol is often called "bad" cholesterol. Your doctor can
judge your risk of heart attack more accurately by determining the amount of cholesterol
carried by your LDL's. If your LDL cholesterol is more than 160 milligrams per
deciliter of blood (mg/dL), it's high risk if you have 2 or more risk factors
or if you have heart disease. Ideally, your LDL cholesterol is below 130. Total
blood cholesterol can indicate your level of risk. If it's 200 mg/dL or over,
your doctor will probably measure your LDL cholesterol level, which is a more
accurate indicator of heart disease.
(HDL's)
High Density Lipoproteins
About one-third to one-fourth of blood cholesterol is carried by high density
lipoprotein or HDL. Medical experts think HDL tends to carry cholesterol away
from the arteries and back to the liver, where it's passed from the body. Some
experts believe HDL helps remove excess cholesterol from atherosclerotic plaques
and thus slows their growth. HDL is known as "good" cholesterol because
a high level of HDL or high density lipoproteins helps to protect against heart
attack. What
Raises Your Blood Cholesterol?
You've probably heard the old saying "you
are what you eat" a thousand times. Well, when it comes to what you eat,
three main factors raise your blood cholesterol level. These are saturated fats,
cholesterol and obesity.
Saturated Fats
All fats are composed
mainly of triglycerides. These, in turn, are composed of "fatty acids."
These fatty acids fall into three categories: saturated, monounsaturated and polyunsaturated.
Of these three, saturated fatty acids are the main culprit in raising blood cholesterol.
Foods
high in saturated fat come from both animals and plants. Animal-based foods containing
lots of saturated fat include butter, beef tallow, lard and poultry fat. Seafood
contains a small amount. Plant-based oils containing saturated fat include coconut
oil, palm kernel oil, palm oil and cocoa butter. There
are four kinds of fats in the foods we eat: (1) saturated, (2) polyunsaturated,
(3) monounsaturated, and (4) trans fatty acids. Most foods contain all three
types of fat, but in varying amounts. Saturated fatty acids, trans fatty acids
and dietary cholesterol raise blood cholesterol.
Saturated Fatty Acids
Saturated fatty acids have all the hydrogen the carbon atoms can hold. Saturated
fats are usually solid at room temperature and they are more stable - that is,
they do not combine readily with oxygen. Saturated fatty acids are the main dietary
culprit in raising blood cholesterol. The main sources of saturated fatty acids
in the typical American diet are foods from animals and some plants.
• Foods
from animals that have high amounts of saturated fatty acids include beef, beef
fat, veal, lamb, pork, lard, poultry fat, butter, cream, milk, cheeses and other
dairy products made from whole milk. These foods also contain dietary cholesterol.
• Foods from plants that contain high amounts of saturated fatty acids
include coconut oil, palm oil and palm kernel oil (often called tropical oils)
and cocoa butter.
Trans Fatty Acids
A fatty acid molecule consists of a chain of carbon
atoms in carbon-carbon double bonds with hydrogen atoms "attached."
In nature, most unsaturated fatty acids are cis fatty acids, meaning the hydrogen
atoms are on the same side of the double carbon bond. In trans fatty acids the
two hydrogen atoms are on opposite sides of the double bond.
Trans double bonds also occur in nature as the result of fermentation in grazing
animals. People eat them in the form of meat and dairy products. Trans double
bonds are also formed during the hydrogenation of either vegetable or fish oils.
To make foods that will stay fresh on the shelf or to get a solid fat product,
such as margarine, food manufacturers hydrogenate polyunsaturated oils. Hydrogenate
means to add hydrogen. When unsaturated fatty acids are hydrogenated, some of
the hydrogen atoms are added on opposite sides of the molecule to the already
attached hydrogen. Cis double bonds convert to trans double bonds, and the fatty
acids become saturated.
In clinical studies, trans fatty acids or hydrogenated fats tend to raise total
blood cholesterol levels but not as much as more saturated fatty acids. Trans
fatty acids also tend to raise LDL ("bad") cholesterol and lower HDL
("good") cholesterol when used instead of cis fatty acids or natural
oils. These changes may increase the risk of heart disease. It's not clear if
trans fats that occur naturally have the same effect on cholesterol and heart
disease as those produced by hydrogenation of vegetable oils.
Because there are no standard methods, it's difficult to estimate the trans fatty
acid content of food items. It's also difficult to estimate intake, especially
long-term intake. On the basis of current data, the American Heart Association
recommends that consumers follow these tips: •
Use naturally occurring, unhydrogenated oil such as canola or olive oil when possible.
• Look for processed foods made with unhydrogenated oil rather than hydrogenated
or saturated fat.
• Use margarine as a substitute for butter, and choose
soft margarines (liquid or tub varieties) over harder, stick forms. Shop for margarine
with no more than 2 grams of saturated fat per tablespoon and with liquid vegetable
oil as the first ingredient.
• French fries, donuts, cookies and crackers
are examples of foods that are high in trans fatty acids.
Polyunsaturated
and Monounsaturated Fatty Acids
Polyunsaturated and monounsaturated fatty
acids make up the total of unsaturated fatty acids. Unsaturated fatty acids have
at least one unsaturated bond - that is, at least one place that hydrogen can
be added to the molecule. They are often found in liquid oils of vegetable origin.
• Polyunsaturated
oils are liquid at room temperature and in the refrigerator. They easily combine
with oxygen in the air to become rancid. Common sources of polyunsaturated fatty
acids are safflower, sesame and sunflower seeds, corn and soybeans, many nuts
and seeds and their oils.
• Monounsaturated oils are liquid at room temperature
but start to become solid at refrigerator temperatures. Peanut oil, olive oil,
canola oil and avocados are sources of monounsaturated fatty acids.
Polyunsaturated
fatty acids tend to help the body get rid of newly formed cholesterol. Thus, they
keep the blood cholesterol level down and reduce cholesterol deposits in artery
walls. Recent research has shown that monounsaturated fatty acids may also help
reduce blood cholesterol as long as the diet is very low in saturated fat.
Both types of unsaturated fatty acids may help lower your blood cholesterol level
when used in place of saturated fatty acids in your diet. But you should be moderate
in your intake of all types of fat. Poly
- or monounsaturated oils - and margarines and spreads made from these oils -
should be used in limited amounts in place of fats with a high saturated fatty
acid content, such as butter, lard or hydrogenated shortenings.
Hydrogenated Fat
During food processing, fats may undergo a chemical
process known as hydrogenation.Hydrogenate means to add hydrogen, or, in the case
of fatty acids, to saturate. The process changes a liquid oil, naturally high
in unsaturated fatty acids, to a more solid and more saturated form. The greater
the degree of hydrogenation, the more saturated the fat becomes. Many commercial
products contain hydrogenated or partially hydrogenated vegetable oils.
Recent studies suggest that these fats may raise blood cholesterol. Hydrogenated
fats in margarine and other fats are acceptable if the product contains no more
than 2 grams of saturated fatty acids per tablespoon. The fatty acid content of
most margarines and spreads is printed on the package or label. Trans
Fatty Acid Facts
Recent studies on the potential cholesterol-raising effects
of trans fatty acids have called attention to the benefits versus risks of choosing
certain foods over others. For example, stick margarines are known to contribute
more trans fatty acids than non-hydrogenated oils or other fats. This has raised
public concern about the use of margarine and whether other options, including
butter, might be a better choice. Here
are some facts:
• Because butter is rich in both saturated fat and cholesterol,
it is potentially a highly atherogenic food (causes the arteries to be blocked).
Most margarine is made from vegetable fat and provides no dietary cholesterol.
• The more liquid the margarine, i.e., tub or liquid forms, the less
hydrogenated it is and the less trans fatty acids it contains. Therefore, margarine
is still a preferable substitute for butter and soft margarines are better than
hard ones.
• The American Heart Association recommends that consumers
shop for margarine with no more than 2 grams of saturated fat per tablespoon and
with liquid vegetable oil as the first ingredient. They should choose soft
margarines over stick forms to limit their intake of cholesterol-raising trans
fatty acids. Diet or lite margarine has less fat, hence, trans fatty acids, than
regular margarine and is a preferable choice.
The AHA's Nutrition
Committee will continue to monitor research in this area. The committee again
strongly advises that healthy Americans over the age of 2 limit their total fat
intake to no more than 30 percent of total calories. If people limit their daily
intake of fats and oils to 5-8 teaspoons, they are not likely to get an excess
of trans fatty acids. —
From the American Heart Association
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