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 unsaturated vegetable
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 unsaturated vegetable 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: brustman@hsph.harvard.edu |
|
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 polyunsaturated fat (corn or soybean oils)
and monounsaturated fat (high in olive and canola oil) 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. "We found no association between total fat
intake and coronary heart disease risk. This probably reflects
the counterbalancing of different types of fat. The picture
changes dramatically when we examine different types of fat.
Our results suggest that replacing saturated and trans
fats in the diet with poly- and monunsaturated sources of
fat is an effective way to reduce coronary heart risk. Reducing
overall fat intake is unlikely to affect heart disease 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 and dairy foods, the
potential beneficial effect of monounsaturated fat is counterbalanced
by the saturated fat in those same food sources. Some vegetable
oils, including canola 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: bfreeman@sph.harvard.edu
Frank Hu, MD, PhD, 617-432-0113
|
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
|
|
Remember to
visit our WRITINGS section
for the latest research articles, scientific studies,
athlete statements and publications by Udo
Erasmus. Want to keep updated on additions
to our website? Visit our EMAIL
UDATES page and sign up for our occasional HTML newsletters! |
|