Low-Fat Diet a Dud for Women's Heart Disease
ESTES PARK, COLO. – Perhaps the least-known finding of the
landmark Women’s Health Initiative was the complete failure of a structured
low-fat diet intervention to lower the risks of coronary heart disease, stroke,
or colon cancer.
"This has gotten very little press. But the results made me
very happy because it gave me one less thing to worry about, which is eating a
low-fat diet. It doesn’t seem to have the same magnitude of effect in women as
it does in men," Dr. Nanette Santoro said at a conference on internal medicine
sponsored by the University of Colorado.
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Dr. Nanette Santoro |
The Women’s Health Initiative Randomized Controlled Dietary
Modification Trial involved 48,835 postmenopausal women aged 50-79 at 40 U.S.
centers who were randomized 40/60 to a low-fat diet intervention or a control
group.
During a mean follow-up of 8.1 years, the diet intervention
and control groups didn’t show any significant differences in rates of coronary
heart disease (hazard ratio, 0.97); stroke (1.02); or cardiovascular disease
(0.98) (JAMA
2006;295:655-66).
Similarly, the event-rate curves for cardiovascular outcomes
as well as for colon cancer in the intervention and control arms were virtually
identical the entire time, with no hint of either early or late benefit for the
low-fat diet (JAMA
2006;295:643-54).
There was a nonsignificant trend for less invasive breast
cancer in the low-fat diet group, where the annualized incidence rate was 0.42%,
a 9% relative risk reduction compared with the 0.45% rate in controls (JAMA
2006;295:629-42).
"So if there’s any possible benefit to a low-fat diet, there
might be some for breast cancer," commented Dr. Santoro, professor and chair of
the department of ob.gyn. at the university.
The diet intervention entailed an intensive behavioral
modification program with 18 group sessions during year 1 and quarterly
maintenance sessions thereafter, with supplemental individualized contact. The
goal was to reduce dietary fat intake by boosting consumption of fruits and
vegetables to at least five servings daily, along with at least six servings of
grains daily. Weight loss goals weren’t part of the study, which was designed in
the 1990s before the obesity epidemic was apparent.
The intervention was effective in terms of accomplishing
lasting dietary change. At baseline, fat accounted for about 38% of total daily
energy intake. After 1 year, this figure dropped to 24% in the diet intervention
arm. At year 6, fat accounted for 29% of daily energy intake in the diet group
compared with 37% in controls, a difference Dr. Santoro called "huge" in light
of the enormous number of participants and the women’s diverse ethnicities and
backgrounds.
The intervention group averaged 3.6 servings per day of fruits
and vegetables at baseline and 4.9 by year 6, compared with 3.8 in controls.
Efforts to increase consumption of grains were unsuccessful, however. The
intervention group averaged 4.7 servings per day at baseline and 4.3 at year 6,
compared with 3.8 in controls.
The Women’s Health Initiative Randomized Controlled Dietary
Modification Trial was funded by the National Heart, Lung, and Blood Institute.
Dr. Santoro reported that she has a research grant from Bayer.
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