Harvard Review: Trans-fats & Heart Disease

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Harvard Review: Trans-fats & Heart Disease

JoAnn Guest

May 02, 2003 19:05 PDT

 

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, snacks and canned foods 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 extremely 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 fats (found in red 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.

---

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 refined carbohydrate diets

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 unrefined oils 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 non-organic 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 unrefined liquid 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 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 but problematic for

health.

 

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.

 

 

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