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Study of Postmenopausal Women
Low-Fat Diet with Fruit, Veggies, Grains Does NOT
Reduce Heart, Breast Cancer or Colon Cancer Risks
Study findings send shock waves through health
care community
Feb. 6, 2006 – Results of new studies were
released today that indicate a diet low in fat, but high in fruit,
vegetables and grains, does not significantly reduce the risk of breast
cancer, colorectal cancer or cardiovascular disease in postmenopausal
women. These findings that run counter to what has been
preached by health experts for years. The three articles will be
published in tomorrow's Journal of the American Medical Association
(JAMA), but they have already stirred up a storm of caution.
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Nutrition |
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The study included nearly 50,000 women followed
over 8 years – clearly no small study.
“These new studies are important and should be
carefully evaluated,” said registered dietitian and physician Christine
Gerbstadt, a spokesperson for the American Dietetic Association.
“It is also important to remember that research
over many years indicates an overall plan of healthful eating –
including plenty of fruits, fiber and vegetables – may help protect
against a number of chronic diseases and conditions, including some
forms of cancer.”
Gerbstadt cautioned that the results of the Women’s
Health Initiative studies should not be seen as an invitation to adopt a
high-fat diet in the belief that lower fat intakes lack health benefits.
Even one of the authors of the study, Mara
Vitolins, expressed concerns. “Nutrition knowledge has progressed
dramatically since the study began,” said the associate professor of
public health sciences at Wake Forest University Baptist Medical Center.
“Today, we know that reducing total fat may not be enough – we need to
focus on the types of fat we eat.”
Vitolins said one explanation for the results is
that the low-fat diet was designed to reduce total fat and didn’t make a
distinction between good fats, such as those found in nuts, fish, and
vegetables oils, and bad fats, such as the saturated fat in meats and
the trans fat used in baked goods and potato chips.
“The study was testing the belief that lowering
total fat would reduce the risk of cancer,” said Vitolins. “Since the
study began, we’ve learned a lot more about how the types of fats we
consume make a difference.”
“The results of this study do not change
established recommendations on disease prevention,” said National Heart,
Lung, and Blood Institute Director Elizabeth G. Nabel, M.D., in an NIH
press release. “Women should continue to get regular mammograms and
screenings for colorectal cancer, and work with their doctors to reduce
their risks for heart disease including following a diet low in
saturated fat, trans fat and cholesterol.”
The JAMA Articles
In the first of the JAMA articles, Ross L. Prentice, Ph.D., of
the Fred Hutchinson Cancer Research Center, Seattle, and colleagues with
the Women’s Health Initiative (WHI) Dietary Modification Trial, examined
the effect of a low-fat diet on the incidence of breast cancer.
The WHI, which began in 1992 with 48,835
postmenopausal women without prior breast cancer, included a dietary
modification intervention consisting of consumption of a reduced amount
of fat (20 percent of energy) and of an increased amount of vegetables
and fruits (5 or more servings a day) and grains (6 or more servings a
day).
The women, aged 50 to 79 years, were randomly
assigned to the dietary modification intervention group (40 percent, n =
19,541) or the comparison group, who were not asked to make dietary
modifications (60 percent, n = 29,294). It has been hypothesized that a
low-fat diet can reduce breast cancer risk, but previous studies have
had mixed results.
The average follow-up time was 8.1 years. Overall,
655 (3.35 percent) women in the intervention group and 1,072 (3.66
percent) women in the comparison group developed invasive breast cancer
during follow-up.
“Among postmenopausal women, a low-fat dietary
pattern did not result in a statistically significant reduction in
invasive breast cancer risk over an 8.1 year average follow-up period.
However, the nonsignificant trends observed suggesting reduced risk
associated with a low-fat dietary pattern indicate that longer, planned,
nonintervention follow-up may yield a more definitive comparison,” the
authors conclude.
In an accompanying editorial, Aman U. Buzdar, M.D.,
of the University of Texas M.D. Anderson Cancer Center, Houston,
commented on the study examining low-fat diet and breast cancer risk.
“After a diagnosis of cancer, patients seek advice
from their physicians and other health care professionals regarding
dietary modifications that could reduce the risk of disease recurrence
and also could decrease their family members’ risk of cancer.
"In addition, many patients follow various popular
diets or use complementary and alternative medicine therapies, such as
various dietary supplements, which have not been evaluated in a rigorous
scientific manner. In contrast, the well-designed rigorous Women’s
Health Initiative dietary modification study by Prentice et al provides
important data that may prove useful for counseling patients.”
Low-Fat Diet Does Not Reduce Risk of Colorectal
Cancer
In a related article, Shirley A. A. Beresford,
Ph.D., of the University of Washington, Seattle, and colleagues with the
Women’s Health Initiative analyzed data from the WHI Dietary
Modification Trial to determine the effect of a low-fat eating pattern
on risk of colorectal cancer in postmenopausal women. Previous trials
examining this association have been inconclusive.
The researchers found that over the 8.1 years of
follow-up, there were 201 cases of invasive colorectal cancer (0.13
percent per year) in the intervention group and 279 (0.12 percent) in
the comparison group. The WHI low-fat eating pattern intervention did
not reduce the risk of invasive colorectal cancers. There was no
evidence of reduced risk for any category of colorectal cancer outcome
associated with the intervention.
“Evidence from this study, along with that from
polyp prevention trials, strongly suggests that lowering dietary fat
intake and increasing fruit, vegetable, and fiber intake in mid to late
life cannot be expected to reduce the risk of colorectal cancer in this
length of time,” the authors write.
Risk of Cardiovascular Disease or Stroke Not
Significantly Decreased With Low-Fat Diet
In a third article from the WHI Dietary
Modification Trial, Barbara V. Howard, Ph.D., of Medstar Research
Institute/Howard University, Washington, D.C., and colleagues with the
Women’s Health Initiative (WHI) examined the effect of a diet low in fat
intake and high in consumption of vegetables, fruits and grains on
cardiovascular disease (CVD) and coronary heart disease (CHD) risk.
After an average of 8.1 years of follow-up, levels
of low-density lipoprotein cholesterol and diastolic blood pressure were
significantly reduced. Levels of high-density lipoprotein cholesterol,
triglycerides, glucose and insulin did not significantly differ in the
intervention vs. comparison groups.
The researchers found that the diet had no
significant effects on incidence of CHD, stroke, CVD, or heart attack.
Trends toward greater reductions in CHD risk were observed in those with
lower intakes of saturated fat or trans fat or higher intakes of
vegetables/fruits.
“To achieve a significant public health impact on
CVD events, a greater magnitude of change in multiple macronutrients and
micronutrients and other behaviors that influence CVD risk factors may
be necessary,” the authors conclude.
Editorial: Dietary Modification and CVD Prevention
– A Matter of Fat
In an accompanying editorial, Cheryl A. M.
Anderson, Ph.D., M.P.H., and Lawrence J. Appel, M.D., M.P.H., of Johns
Hopkins University Bloomberg School of Public Health and School of
Medicine, Baltimore, discuss the findings of Howard et al.
“Despite null findings from the WHI Dietary
Modification Trial, dietary changes can have powerful, beneficial
effects on CVD risk factors and outcomes. To reduce the risk of CVD,
individuals should maintain a desirable body weight, be physically
active, avoid tobacco exposure, and eat a diet consistent with national
guidelines. Additional results from the WHI Dietary Modification Trial,
likely forthcoming, should provide valuable evidence that will refine
these recommendations and further enhance CVD prevention efforts in
women.”
“As a registered dietitian, I encourage everyone to
follow the 2005 Dietary Guidelines for Americans, which recommend
keeping total fat intake between 20 percent to 35 percent of daily
calories,” added Gerbstadt, speaking for the American Dietetic
Association The Dietary Guidelines recommend most fats come from sources
like fish, nuts and vegetable oils.
“Obesity remains this country’s number-one public
health problem, especially given how closely it is related to many
life-threatening conditions, including several forms of cancer, coronary
heart disease, diabetes and metabolic syndrome,” Gerbstadt said. “It has
been shown that achieving and maintaining a healthy weight, plus
increased physical activity, can help reduce your likelihood of these
conditions.”
Editor’s Note: The WHI program was funded by the
National Heart, Lung, and Blood Institute of the National Institutes of
Health, Department of Health and Human Services. For the financial
disclosures of the authors, please see the JAMA articles.
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