Fats and Cholesterol - The Good, The Dietary Fats and Heart Disease--Beyond
Bad, and The Healthy Diet the "30%" Recommendation
"Eat a low-fat, low-cholesterol diet." Many health agencies, including the
Most of us have heard this simple American Dietetic Association, the
recommendation so often over the past American Diabetes Association, and the
two decades that we can recite it in American Heart Association, once
our sleep. Touted as a way to lose
recommend limiting fat intake to 30% or
weight and prevent cancer and heart less of total daily calories as a
disease, it's no wonder much of the means of preventing disease. Today,
nation - and food producers - hopped on these recommendations focus on limiting
board. intake of saturated fat, and have
relaxed a bit with regard to total fat
Unfortunately, this simple message is intake. That's a move in the right
now largely out of date. Detailed direction, because there is no good
research -much of it done at Harvard - evidence for any particular "optimal"
shows that the total amount of fat in amount of total fat in a healthy diet.
the diet, whether high or low, isn't
really linked with disease. What really The relation of fat intake to health
matters is the type of fat in the is one of the areas that Harvard
diet.(1) Bad fats increase the risk for researchers have examined in detail
certain diseases and good fats lower over the last 20 years in two large
the risk. The key is to substitute good studies. The Nurses' Health Study and
fats for bad fats. the Health Professionals Follow-up
Study have found no link between the
And cholesterol in food? Although it overall percentage of calories from fat
is still important to limit the amount and any important health outcome,
of cholesterol your eat, especially if including cancer, heart disease, and
you have diabetes, dietary cholesterol weight gain.
isn't nearly the villain it's been
portrayed to be. Cholesterol in the What was important in these studies
bloodstream is what's most important. was the type of fat in the diet.(3)
High blood cholesterol levels greatly There are clear links between the
increase the risk for heart disease. different types of dietary fats and
But the average person makes about 75% heart disease. Logically, most of the
of blood cholesterol in his or her influence that fat intake has on heart
liver, while only about 25% is absorbed disease is due to its effect on blood
from food. The biggest influence on cholesterol levels.
blood cholesterol level is the mix of
fats in the diet. Ounce for ounce, trans fats are far
worse than saturated fats when it comes
The Cholesterol--Heart Disease to heart disease. The Nurses' Health
Connection Study found that replacing only 30
calories (7 grams) of carbohydrates
Cholesterol is a wax-like substance. every day with 30 calories (4 grams) of
The liver makes it and links it to trans fats nearly doubled the risk for
carrier proteins called lipoproteins heart disease.(4) Saturated fats
that let it dissolve in blood and be increased risk as well, but not nearly
transported to all parts of the body. as much.
Why? Cholesterol play essential roles
in the formation of cell membranes, For the good fats, there is consistent
some hormones, and vitamin D. evidence that high intake of either
monounsaturated or polyunsaturated fat
Too much cholesterol in the blood, lowers the risk for heart disease. In
though, can lead to problems. In the the Nurses' Health Study, replacing 80
1960s and 70s, scientists established a calories of carbohydrates with 80
link between high blood cholesterol calories of either polyunsaturated or
levels and heart disease. Deposits of monounsaturated fats lowered the risk
cholesterol can build up inside for heart disease by about 30 to 40
arteries. These deposits, called percent.(3)
plaque, can narrow an artery enough to
slow or block blood flow. This Fish, an important source of the
narrowing process, called polyunsaturated fat known as omega-3
atherosclerosis, commonly occurs in fatty acid, has received much attention
arteries that nourish the heart (the in the past for its potential to lower
coronary arteries). When one or more heart disease risk. And there have
sections of heart muscle fail to get been some studies to back this up,
enough blood, and thus the oxygen and although not all have shown consistent
nutrients they need, the result may be benefits. One large trial, however,
the chest pain known as angina. In found that by getting 1 gram per day of
addition, plaque can rupture, causing omega-3 fatty acids over a 3.5 year
blood clots that may lead to heart period, people who had survived a heart
attack, stroke, or sudden death. attack could lower their risk of dying
Fortunately, the buildup of cholesterol from heart disease by 25 percent.(5)
can be slowed, stopped, and even The study participants got their
reversed. omega-3s from a capsule - getting a
gram a day from fish would mean eating
Cholesterol-carrying lipoproteins play a serving a day of fatty fish, such as
central roles in the development of mackerel, salmon, sardines, or
atherosclerotic plaque and swordfish.
cardiovascular disease. The two main
types of lipoproteins basically work in Eating fish may help prevent heart
opposite directions. disease or deaths from heart disease in
several ways. it may replace red meat
Low-density lipoproteins (LDL) carry or other less-healthy sources of
cholesterol from the liver to the rest protein. And the omega-3 fats in fish
of the body. When there is too much LDL appear to protect the heart against the
cholesterol in the blood, it can be development of erratic and potentially
deposited on the walls of the coronary deadly rhythm disturbances. Although
arteries. Because of this, LDL more research is needed, adding fish to
cholesterol is often referred to as the the diet may help protect you from
"bad" cholesterol. heart disease, and it doesn't have any
known risks. The American Heart
High-density lipoproteins (HDL) carry Association currently recommends that
cholesterol from the blood back to the everyone eat at least two servings of
liver, which processes the cholesterol fish a week.(6)
for elimination from the body. HDL
makes it less likely that excess Dietary Fats and Cancer
cholesterol in the blood will be
deposited in the coronary arteries, Heart disease is not the only
which is why HDL cholesterol is often condition that has been linked with fat
referred to as the "good" cholesterol. intake. Researchers once suspected an
association between dietary fat and
In general, the higher your LDL and certain cancers. Here again, the type
the lower your HDL, the greater your of fat - and not the total amount -
risk for atherosclerosis and heart seemed to be most important.
disease.
Breast Cancer
For adults age 20 years or over, the
latest guidelines from the National By the early 1980s, most nutrition
Cholesterol Education Program recommend experts believed that dietary fat was a
the following optimal levels: major cause of breast cancer.(7, 8)
This thinking was largely based on
* Total cholesterol less than 200 international comparisons showing
milligrams per deciliter (mg/dl) higher breast cancer rates in countries
* HDL cholesterol levels greater with higher per capita fat intake. But
than 40 mg/dl such comparisons are very broad in
* LDL cholesterol levels less than nature. As more detailed studies were
100 mg/dl performed over the next couple of
decades, the apparent link between
Dietary Fat, Dietary Cholesterol, and total fat intake and breast cancer has
Blood Cholesterol Levels faded.(9)
One of the most important determinants Many newer studies - including those
of blood cholesterol level is fat in by Harvard researchers - of different
the diet - not total fat, as mentioned types of fat have failed to find a link
already, but specific types of fat. with breast cancer. However, some
Some types of fat are clearly good for European studies have reported
cholesterol levels and others are suggestive findings of lower breast
clearly bad for them. cancer risk among women with a high
intake of monounsaturated fats (mainly
Cholesterol in food in the form of olive oil).(10, 11)
While it is well known that high blood Colon Cancer
cholesterol levels are associated with
an increased risk for heart disease, As with breast cancer, international
scientific studies have shown that comparisons initially suggested an
there is only a weak relationship association between total dietary fat
between the amount of cholesterol a intake and colon cancer risk. But later
person consumes and their blood studies contradicted these earlier
cholesterol levels or risk for heart findings and revealed instead an
disease. For some people with high association that was weak at best.
cholesterol, reducing the amount of Although fat intake doesn't seem to
cholesterol in the diet has a small but increase colon cancer risk, high
helpful impact on blood cholesterol consumption of red meat still does
levels. For others, the amount of appear to do so.(12)
cholesterol eaten has little impact on
the amount of cholesterol circulating Prostate Cancer
in the blood.
Although the exact connection between
In a study of over 80,000 female dietary fat and prostate cancer is far
nurses, Harvard researchers actually from clear, there is some evidence that
found that increasing cholesterol diets high in animal fat and saturated
intake by 200 mg for every 1000 fat increase prostate cancer risk.
calories in the diet (about an egg a However, some studies have also shown
day) did not appreciably increase the no association, while others have
risk for heart disease.(2) implicated unsaturated fats. Clearly
much more research is needed to clear
Eggs up the exact links between dietary fat
and prostate cancer.
Long vilified by well-meaning doctors
and scientists for their high Other Cancers
cholesterol content, eggs are now
making a bit of a comeback. Recent Preliminary research has also linked
research by Harvard investigators has the intake of certain kinds fat with
shown that moderate egg consumption--up other cancers, though much more
to one a day--does not increase heart research is needed to confirm these
disease risk in healthy individuals.(2) results. In the Nurses' Health Study,
While it's true that egg yolks have a Harvard researchers found that a high
lot of cholesterol--and, therefore may intake of trans fats increased the risk
slightly affect blood cholesterol for non-Hodgkin's lymphoma and that a
levels--eggs also contain nutrients high saturated fat intake increased the
that may help lower the risk for heart risk for endometrial cancer.
disease, including protein, vitamins
B12 and D, riboflavin, and folate. Dietary Fat and Obesity
So, when eaten in moderation, eggs can It is a common belief that the more
be part of a healthy diet. People with fat you eat, the more body fat you put
diabetes, though, should probably on, and the more weight you gain. This
limit themselves to no more than two or belief has been bolstered by much of
three eggs a week, as the Nurses' the nutrition advice given to people
Health Study found that for such over the past decade, which has focused
individuals, an egg a day might on lowering total fat intake while
increase the risk for heart disease. increasing carbohydrate intake. But it
Similarly, people who have difficulty isn't completely true, and the advice
controlling their blood cholesterol may has been misguided. For example, while
also want to be cautious about eating Americans have gradually decreased the
egg yolks and choose foods made with proportion of calories they get from
egg whites instead. fat over the last decade, rates of
obesity have increased steeply.
Dietary Fats
Over the short term, following a
The Bad Fats low-fat diet does lead to weight loss.
But so does following a high-fat,
Some fats are bad because they tend to low-carbohydrate diet. Actually, almost
worsen blood cholesterol levels. any diet that helps you take in fewer
calories works over the short term. In
Saturated Fats other words, low-fat diets appear to
offer no apparent advantages over diets
Saturated fats are mainly animal fats. with fat levels close to the national
They are found in meat, seafood, average.
whole-milk dairy products (cheese,
milk, and ice cream), poultry skin, and Although more research is needed, a
egg yolks. Some plant foods are also prudent recommendation for losing
high in saturated fats, including weight or maintain a healthy weight is
coconut and coconut oil, palm oil, and to be mindful of the amount of food you
palm kernel oil. Saturated fats raise eat in relation to the amount of
total blood cholesterol levels more calories you burn in a day. Exercising
than dietary cholesterol because they regularly is especially beneficial.
tend to boost both good HDL and bad LDL
cholesterol. The net effect is The Bottom Line: Recommendations for
negative, meaning it's important to Fat Intake
limit saturated fats.
Although the different types of fat
Trans Fats have a varied - and admittedly
confusing - effect on health and
Trans fatty acids are fats produced by disease, the basic message is simple:
heating liquid vegetable oils in the chuck out the bad fats and replace them
presence of hydrogen. This process is with good fats. Try to limit saturated
known as hydrogenation. The more fats in your diet and eliminate trans
hydrogenated an oil is, the harder it fats and replace them with
will be at room temperature. For polyunsaturated and monounsaturated
example, a spreadable tub margarine is fats.
less hydrogenated and so has fewer
trans fats than a stick margarine. The trickiest of these to attack are
the trans fats. That's because they
Most of the trans fats in the American lurk in many different types of foods
diet are found in commercially and aren't always included on the food
prepared baked goods, margarines, snack label. But as awareness about trans
foods, and processed foods. fats increases, more "trans-fat" free
Commercially prepared fried foods, like products are becoming available. Now
French fries and onion rings, also there's even a trans fat-free Crisco!
contain a good deal of trans fat. Labeling of trans fat content has long
been up to the food maker's discretion.
Trans fats are even worse for However, a report on trans fats from
cholesterol levels than saturated fats the Institute of Medicine concluding
because they raise bad LDL and lower that there is no safe level of trans
good HDL. While you should limit your fats in the diet (13) has finally
intake of saturated fats, it is prompted the Food and Drug
important to eliminate trans fats from Administration to require that all
partially hydrogenated oils from your Nutrition Facts food labels list trans
diet. fats by January 1, 2006. Some foods -
mostly those that are trans-fat-free -
The Good Fats already list trans fats. Until all
foods do, it will take some detective
Some fats are good because they can work to determine if a food contains
improve blood cholesterol levels. trans fats. Check the ingredient list
for "hydrogenated oils." The higher up
Unsaturated Fats--Polyunsaturated and these are listed, the more trans fats
Monounsaturated the food contains.
Unsaturated fats are found in products Tips for lowering trans fat intake:
derived from plant sources, such as
vegetable oils, nuts, and seeds. There * Choose liquid vegetable oils or
are two main categories: a soft tub margarine that is contains
polyunsaturated fats (which are found little or no trans fats.
in high concentrations in sunflower, * Reduce intake of commercially
corn, and soybean oils) and prepared baked goods, snack foods, and
monounsaturated fats (which are found processed foods, including fast foods.
in high concentrations in canola, To be on the safe side, assume that all
peanut, and olive oils). In studies in such produts contain trans fats unless
which polyunsaturated and they are labeled otherwise.
monounsaturated fats were eaten in * When foods containing
place of carbohydrates, these good fats hydrogenated or partially hydrogenated
decreased LDL levels and increased HDL oils can't be avoided, choose products
levels. that list the hydrogenated oils near
the end of the ingredient list.