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