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Diet,
Exercise Effective in Preventing Cancer
Oct. 28,
2003 - Though the concept of healthy living has long included such
recommendations as diet and exercise, clinical evidence suggests that
these activities may be more powerful in preventing cancer than
previously thought, according to research presented yesterday at the
American Association for Cancer Research Second Annual International
Conference on Frontiers in Cancer Prevention Research.
"These
studies provide us with evidence about the mechanisms by which modest
changes in daily habits can alter the risk of cancer," said John
Potter, M.D., Ph.D., of the Fred Hutchison Cancer Research Center,
Seattle, Wash.
"Here,
for instance, are some quite specific data on the way in which weight
loss and exercise can alter body chemistry, so as to favor a reduction
in risk. This adds to the empirical findings of lower risk of cancer
with healthier lifestyles that can act as a spur to those who need to
know how it works before they are willing to change," he added.
The Effects of Weight Loss and Weight
Gain on Biomarkers of Breast Cancer Risk (Abstract 1451)
Pre-menopausal weight gain is associated with an increased risk of
post-menopausal breast cancer, according to researchers from
Manchester, England, who examined a weight-loss program to identify
the link between weight loss and risk of developing cancer. Results
showed that even a small weight loss, just five percent of an
individual's body weight, may lower the risk of developing breast
cancer. In the trial, 79 women with a family history of breast cancer
who had gained significant amounts of weight as adults were divided
into two different diet regimens: a calorie-restricted/exercise,
weight-loss program; and a standard diet with only exercise advice.
Changes
were measured by body weight, waist circumference, percent body fat,
total subcutaneous and intrabdominal fat, insulin, testosterone and
SHGB (sex hormone binding globulin), which impacts levels of
bioavailable estrogen. The effects of losing more than five percent,
or between zero and five percent of body weight, were examined. Only
women losing more than five percent of their body weight experienced
notable declines in waist circumference; percent body fat; total,
subcutaneous and intra-abdominal fat; testosterone and insulin levels;
and increases in SHBG.
Biomarkers for breast cancer risk pointed to positive benefits from a
weight loss of five percent when compared to the standard trend of
weight gain among overweight women with a family history of breast
cancer.
"Until
now, the general perception suggested that weight loss had to be
significant in order to make a difference in disease prevention," said
Michelle Harvie, Ph.D., of the South Manchester University Hospitals
in Manchester and lead author of the study. "We hope this study will
prove to women that a small effort can go a long way."
Researchers are currently examining the effects of this weight loss
intervention over a 12-month period, in order to determine the
potential long-term benefits.
The Association Between Physical
Activity Levels and Mammographic Breast Density in Pre- and
Post-Menopausal Women: The Health, Eating, Activity and Lifestyle
(HEAL) Study (Abstract 1481)
Women
with dense breast tissue are at an increased risk of breast cancer
when compared to women with less dense breast tissue. In this study of
1,223 women, researchers found that lower amounts of dense breast
tissue were associated with higher physical activity levels in
premenopausal women with a BMI (body mass index) less than 30,
providing further evidence that exercise may protect against breast
cancer. Participants were enrolled in the Health, Eating, Activity and
Lifestyle (HEAL) study, a multicenter study designed to examine the
associations between physical activity, diet, weight, hormones, breast
density, and other influences on breast cancer prognosis among newly
diagnosed breast cancer survivors. Physical activity levels and breast
density for this analysis were determined from information and
mammographic films from the year prior to diagnosis.
After
adjusting for age, ethnicity, education, BMI, study site, number of
children, and hormone-replacement use, a statistically significant 17
percent difference in breast tissue density was observed between the
least active and most active pre-menopausal women with a BMI less than
30. Researchers found the association between physical activity and
breast density only among leaner pre-menopausal women, and not among
heavier pre-menopausal women or post-menopausal women in any BMI
category.
"We're
pleased that we observed an association between physical activity and
breast density. We've known that breast density is related to breast
cancer risk, and that breast density may change throughout a lifetime.
Factors that change breast density may also change breast cancer
risk," said Melinda Irwin, Ph.D., MPH, of Yale University and Yale
Cancer Center, and lead author of the study. "This information
provides further evidence of the many benefits of regular exercise
that could be used to motivate women to be more physically active,"
she added.
Dietary Fat and Carbohydrates: Role in
Prevention of Prostate Cancer Progression and TRAMP Mice (Abstract
1217)
Previous
studies have suggested a link between the amount of saturated fat in
the diet and the risk of progression to advanced prostate cancer. This
study, led by Ada Elgavish, Ph.D., at the University of Alabama at
Birmingham, compared the relative risk of developing advanced prostate
cancer with a low-carbohydrate or a low-fat diet provided ad libitum
(as much as wished), beginning before tumors developed and continuing
until middle age.
"In the
low-fat versus low-carbohydrate debate, we're finding that under
conditions in which diet is provided ad libitum, a diet with fewer
carbohydrates may be more effective in preventing progression to
advanced, lethal prostate cancer than a diet with low fat content,"
said Dr. Elgavish, the lead author of the study.
"However,
the results of this study are preliminary. Men should talk to their
doctors before changing their diets," she added. The study was carried
out in TRAMP mice, a TRAnsgenic Mouse model of Prostate cancer
developed by Dr. Greenberg and associates at Baylor College of
Medicine in Houston. These mice are biologically engineered to develop
prostate cancer after puberty. The objective of the present study was
to test the possibility of delaying progression to advanced prostate
cancer by diet modifications.
Two
groups of genetically compromised TRAMP mice were fed diets containing
the same amount of calories, with either 10 percent or 45 percent fat
(mostly lard); 17 and 13 mice, respectively. Carbohydrates, mostly
corn starch and sucrose, replaced fat in the low fat diet. Researchers
measured food intake and body weight throughout the 23-week study.
After the onset of middle age, mice fed the 45 percent fat diet had a
consistently higher body weight and the increase was due to higher
body fat. When the study ended, 95 percent of the mice fed the 45
percent fat diet had survived, as compared with only 68.2 percent of
those fed with the 10 percent fat diet. In addition, the percentage of
mice with advanced prostate cancer in the 45 percent fat group was
one-third of that in the group fed the 10 percent fat diet.
Diet and Risk of Breast Cancer in
Shanghai, China (Abstract 1274)
International incidence rates of breast cancer vary drastically, and
recent studies have shown dramatically increased cancer risk levels in
women migrating from China to Hong Kong to the United States. This
information suggests that environmental differences may contribute to
breast cancer risk, including extremely different dietary intakes in
various regions of the world.
In this
study, 378 women in Shanghai, China, who were diagnosed with breast
cancer were compared with 1,070 age-matched, unaffected control women.
Dietary intake was determined through the completion of an in-depth
food frequency questionnaire, which recorded such factors as food
group and caloric intake.
Researchers found that consumption of four or more servings of fruits
and vegetables per day was associated with a significantly lower
breast cancer risk. However, no association was seen between intake of
soy or soy products and breast cancer risk. The results provide
support for the benefits of eating fruits and vegetables to prevent
cancer, and also offer one of the first analyses between different
botanical groups and breast cancer risk.
"The
study provides further support suggesting that low fruit and vegetable
intake in the Western diet may be a major factor in the risk of
developing breast cancer," said Jackelin Shannon, Ph.D., R.D.,
assistant professor of public health and preventive medicine in the
Oregon Health and Science University School of Medicine, member of the
OHSU Cancer Institute, and lead author of the study. "Women need to
modify their diets to include more fruits and vegetables to help
prevent the disease," she said.
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