Harvard Review: Trans-fats & Heart Disease

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Harvard Review: Trans-fats & Heart Disease JoAnn Guest May 02, 2003 19:05

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Harvard Review of evidence

verifies that eating " trans-fats "

increases risk of Heart Disease

 

http://www.udoerasmus.com/articles/reviews/item4.htm

 

Boston, MA -- Over the course of the last decade, numerous studies have

examined the relationship between the consumption of trans fatty acids

found in partially " hydrogenated " oils and coronary heart disease (CHD).

A comprehensive review of the scientific evidence confirms that eating

trans fatty acids increases the risk of CHD.

 

The review, published in the June 24, 1999, New England Journal of

Medicine, is authored by researchers at the Harvard School of Public

Health and the Wageningen Centre for Food Sciences in the Netherlands.

 

Lead author, Alberto Ascherio, said " Coronary heart disease kills

500,000 Americans each year. According to our estimations, if trans fats

were replaced by monounsaturated oils, we would expect to see at least

30,000 fewer persons die prematurely from CHD each year. "

 

Trans fatty acids are found in most margarines, in many commercially

baked goods, and in the fats used for deep-frying in many restaurants.

The commercial advantages trans fats hold over monounsaturated oils is

that they are solid at room temperature, they can remain on the shelf

for a longer time before becoming rancid, and they allow for deep-frying

at higher temperatures.

 

" Because of concerns that trans fatty acids increase risk of CHD, " said

Ascherio. " The Food and Drug Administration is considering new

regulations for nutrition labels that will require manufacturers to

report the amount of trans fatty acids. "

--------------------------------

 

 

Under current guidelines, a consumer who is trying to be heart-healthy

might choose a product that is labeled as being low in cholesterol and

saturated fat, but which is high in harmful " trans- fats " .

 

The researchers reviewed more than 25 metabolic and epidemiological

studies. The metabolic studies showed that trans-fats have a two-pronged

harmful effect on blood cholesterol levels: trans fats increase

" low-density " lipoprotein cholesterol (LDL-- " bad cholesterol " ) and

decrease " high-density " lipoprotein cholesterol (HDL-- " good

cholesterol " ).

 

The epidemiological studies tracked people’s eating habits and examined

occurrence of CHD later in their lives. These studies found a link

between consumption of trans fats and CHD that was higher than expected

from the results of the metabolic studies.

 

" We don’t fully understand all of the ways that trans fats increase risk

of CHD, " said Ascherio, " but it seems clear that they do increase risk. "

 

Ascherio and colleagues urge the food industry to replace the partially

hydrogenated fats used in foods and in food preparation with

unhydrogenated oils: " Such a change would substantially reduce the risk

of coronary heart disease at a modest cost. "

 

Alberto Ascherio is an associate professor of nutrition and epidemiology

at the Harvard School of Public Health.

 

See also: Trans Fatty Acids and Coronary Heart Disease, The New England

Journal of Medicine -- June 24, 1999 -- Vol. 340, No. 25.

 

 

 

 

 

For further information, please contact:

Bob Brustman

Harvard School of Public Health

Department of Nutrition

665 Huntington Avenue

Boston, MA 02115

Phone: 617-432-3952

Email: brus- ;

 

 

 

 

 

 

 

 

 

 

Study shows how different types of dietary fat

affect coronary heart disease risk

Harvard School of Public Health PRESS RELEASE

For immediate release: November 18, 1997.

 

 

 

Boston, MA -- Harvard School of Public Health and Brigham and Women's

Hospital researchers report from the Nurses' Health Study that it is the

type of dietary fat, not total fat, that affects coronary heart disease

risk.

 

Saturated fat (found in meats and dairy foods) and trans unsaturated

fat (margarine, packaged cookies, crackers, and fast foods) increase the

risk of coronary heart disease. A relatively higher intake of

monounsaturated fat (high in extra-virgin olive oils) actually reduces

risk. The study is reported in this week's New England Journal of

Medicine.

 

" Results from previous studies have been mixed concerning a possible

association between fat and risk of coronary heart disease. This has

probably occurred because some studies have been small and did not take

into account different types of fat. Because numerous metabolic studies

have strongly suggested different fats act in different ways to affect

blood lipid levels, we were very interested in examining the impact of

different types of fat on coronary heart disease risk, " comments Frank

Hu, MD, PhD, lead author on the study and a research fellow at the

Harvard School of Public Health.

 

" In this large prospective study of nurses, which included over 900

cases of heart disease, we enhanced our ability to examine the strength

of the associations between fat and heart disease risk by obtaining

repeated measurements of fat intake, " continues Dr. Hu. Our results

suggest that replacing saturated and trans fats in the diet with

monunsaturated sources of fat is an effective way to reduce coronary

heart risk. "

 

--

 

The study also finds that trans fat is associated with the highest

relative risk of coronary heart disease, twice that associated with the

same intake of energy from carbohydrates.

 

This large effect is probably explained, say the researchers, not only

by the impact of trans fat on blood lipid levels but its interference

with essential fatty-acid metabolism and ability to elevate triglyceride

levels.

 

While both monounsaturated and saturated fats are present in meats, the

potential beneficial effect of monounsaturated fat is counterbalanced by

the saturated fat in those same food sources. Some oils, including

avocado and olive oils, excellent sources of monounsaturated fat, are

not yet widely consumed by Americans.

 

The authors point out that the high carbohydrate diet recommended by

some heart disease prevention programs, which are intended to lower LDL

levels, also lower the " good " HDL levels. Consequently, an alternative

strategy -- changing the composition of fats in the diet with the dual

aims of lowering LDL and raising HDL levels -- may be a better way to

lower coronary heart disease risk.

 

The Nurses' Health Study is an on-going prospective study of women, age

30-55 at enrollment in 1976. The study is directed by Frank Speizer, MD,

Brigham and Women's Hospital and Harvard Medical School. Subjects were

subsequently followed every two years answering questionnaires

concerning their diet, lifestyle and health.

 

 

 

For further information, please contact:

Beverly Freeman, Director of Public Affairs

617-432-3863, email: bfre-

 

Frank Hu, MD, PhD, 617-432-0113

 

 

 

 

 

Nutrition Researcher Frank Hu: Fat Quality More Important Than Quantity

Around the School: News and Notices of the Harvard School of Public

Health

April 30, 1999.

 

 

Frank Hu, research associate in the Department of Nutrition, has been

receiving a lot of attention lately from the popular media. The reason

for this attention is that he has been lead author of a number of

studies that have produced good news about a popular and necessary

activity: eating.

 

Specifically, his work has examined the relationship between diet and

heart disease. In November, 1998, Hu reported in the British Medical

Journal that eating nuts reduced the risk of coronary heart disease in

women. In April, his paper in the Journal of the American Medical

Society showed that there was no link between moderate egg consumption

and heart disease. Most recently, in the May issue of the American

Journal of Clinical Nutrition, his analysis demonstrates that linolenic

acid, an omega-3 fatty acid found in some vegetable oils and salad

dressing products, may protect against fatal heart attacks.

 

Hu's work has comprised a series of collaborations with Walter Willett,

Fredrick John Stare professor of epidemiology and nutrition, and other

colleagues in the Nurses Health Study and the Health Professionals

Follow-up Study. This same group, in 1997, published an article in the

New England Journal of Medicine indicating that total fat consumption

was less important to heart disease than the type of fat consumption.

 

" The problem is that 'total fat' is not a useful term, " said Hu. " There

are good fats and bad fats. In the public's mind, fat has become public

enemy number one. Reducing dietary fat has become a priority. But the

truth is that if you reduce your total fat consumption, you're also

reducing the amount of good fats that you eat--fats that have a

protective effect against heart disease. "

 

Bad fats are those that are frequently found in dairy, meat, and other

animal products. These are saturated fats that have been shown to

increase levels of low-density-lipoprotein (LDL) cholesterol in the

bloodstream. If the body has more LDL cholesterol than it requires, the

excess is deposited on the walls of arteries in the form of plaque. Too

much plaque and the arteries become plugged--a condition known as

arteriosclerosis. When arteries in the heart become clogged, it causes a

heart attack. If arteries that lead to the brain are plugged, then the

result is a stroke.

 

Good fats, on the other hand, are found in liquid vegetable oils. These

include monounsaturated fats and polyunsaturated fats. These fats lower

LDL cholesterol levels, resulting in lower risk of cardiovascular

disease.

 

--

 

 

Trans fats muddy the waters. " Trans fats are vegetable oils that are

partially hydrogenated, " explained Hu. " Adding hydrogen to the oils

makes them solid at room temperature, a characteristic that makes them

useful in the production of baked goods. Products made with hydrogenated

oils have long shelf lives. " Unfortunately, trans fats are more

dangerous than saturated fats. Not only do trans fats increase LDL

cholesterol levels like saturated fats, they also reduce levels of HDL

cholesterol--the helpful cholesterol. Trans fats do double harm. "

 

Explicating the relationships between types of fat and risk of heart

disease has been the basis of Hu's recent work. " We did the nut study to

prove our point. Many people avoid nuts because they're notoriously high

in fats--up to 80% of the energy in a nut comes from its fat content.

Therefore, many people assumed that eating nuts would increase risk of

heart disease. But, because nuts contain primarily unsaturated fats,

eating nuts substantially reduces risk of heart disease. "

 

Next, Hu and his colleagues turned to eggs: " Eggs have been perceived as

unhealthy food for many years because of their high cholesterol content.

People have assumed that egg consumption would lead to increased risk of

heart disease. "

 

Hu was not surprised by the results of the study. " Moderate egg

consumption, which we defined as one egg per day, is not associated with

increased risk of heart disease. These results are consistent with data

from previous metabolic studies that suggested relatively small effects

of dietary cholesterol on cholesterol levels in the bloodstream, " he

said. " The slight adverse effect of an egg's cholesterol content is

balanced by the beneficial contents of its other nutrients. "

 

The researchers did find, however, that egg consumption is dangerous for

people with diabetes, possibly because of their altered ability to

metabolize cholesterol. Moderate egg consumption led to a 40-to-50%

increased risk of heart disease for diabetics.

 

Hu's next project is an examination of the relationships between types

of fat consumption and heart disease in people with diabetes. " Previous

studies have demonstrated that monounsaturated fat has particular

benefits on blood lipids and glucose response among diabetics, " said Hu.

" But the effects of monounsaturated fat on risk of heart disease among

diabetics have not been studied. "

 

Around the School

is published weekly by the Office of Academic Communications

Harvard School of Public Health

665 Huntington Ave., 1204

Boston, Massachusetts 02115

617-432-3952

 

 

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