a Good Diet
By Ira Dreyfuss, AP
Cancer Society, worried about a nation that does too little exercise
and grows more obese, is putting a new emphasis on exercise as a
way to reduce the risk of getting sick and dying of cancer.
The five-year update
of the society's nutrition and activity guidelines says the evidence
now is convincing that exercise reduces risk of colorectal and breast
cancer. The report says there also is a probable benefit against endometrial
cancer, and activity may help against other forms of cancer as well.
A medical panel
that weighed the latest research says activity apparently works
directly to lower the risk, and provides an added indirect benefit
if the exercise also keeps a person's weight down. The experts found
what they describe as convincing evidence that weight control, through
proper nutrition or physical activity, independently reduces risk.
exercised and controlled weight, the number of Americans who die
of cancer would drop by about one third, the guidelines said. About
an equal number of new cases could be prevented. The society estimates
almost 1.3 million new cancer diagnoses this year. More than 500,000
people die of cancer.
The idea that
one-third of cancer cases could be prevented through calorie control
and exercise is not new. But the emphasis on physical activity is
new, said Dr. Anne McTiernan of Fred Hutchinson Cancer Research
Center in Seattle, a coauthor of the guidelines. "Five years ago,
we didn't have the amount of data we have now," she said.
minimum recommendation for cancer prevention in adults is at least
30 minutes of moderate activity, such as a brisk walk five days
a week. That's in line with the Surgeon General's recommendations
for overall good health and the American Heart Association's recommendations
for cardiovascular health.
can control weight, improving energy metabolism and reducing circulating
concentrations of insulin. "Physical activity helps to prevent adult-onset
diabetes, which has been associated with increased risk of cancers
of the colon, pancreas and possibly other sites," the report said.
Risks of some
forms of cancer can be double among the overweight and obese, but
the data are cloudy because the studies were not uniform on what
they consider too much weight, McTiernan said.
45 minutes or more of moderate to vigorous activity five or more
days a week may enhance reductions in breast and colon cancer risk,
the guidelines said. Vigorous activity can range from jogging to
martial arts, basketball or masonry work.
This much exercise
can reduce the risk of colon cancer by almost half and breast cancer
by a third, McTiernan said. Exercise reduces circulating levels
of estrogen, which has been linked to higher breast cancer risk
in postmenopausal women, she said. Exercise reduces other hormones
that can raise the risk of colon cancer, and speeds material through
the bowel before any cancer-causing agents can linger against the
bowel wall, she said.
also call for children and adolescents to do at least 60 minutes
a day of moderate-to-vigorous physical activity, five days a week.
The goal is to create lifetime habits that will keep the youngsters
out of the 55 percent of American adults who now are overweight
or obese, McTiernan said.
And the guidelines
say the overweight should lose weight. Studies have not found that
cancer risk falls if people lose weight, but experts suspect risk
would fall because studies do show a lower cancer risk among people
who are not overweight.
And the experts
say communities should provide more facilities for physical activity,
including safe and attractive places to walk and run.
the recommendations: People should eat more fruits and vegetables.
This has been linked to lower rates of lung, oral, esophageal, stomach
and colon cancer. High-fat diets have been associated with increase
in risk of cancers of the colon and rectum, prostate and endometrium.
is published in the March issue of the society's publication CA
A Cancer Journal for Clinicians. In an accompanying commentary,
Dr. Walter C. Willett of Harvard School of Public Health praises
the report as a clear call for action in cancer prevention.
and the better-educated already have been keeping their weight down
and their activity levels up, and thereby reduce their cancer risk,
Willett said. "Unfortunately, another part of the population, for
various reasons we have to understand better, is not taking advantage,
and that part of the population's health status is almost for sure
getting worse," he said.
exercise is a good thing, the society may be overstating its benefits,
said Louise Brinton, chief of environmental epidemiology at the
National Cancer Institute.
In breast cancer,
for instance, it's clear that obesity raises the risk, but it's
not established that exercise will drive down the risk unless it
also lowers the exerciser's weight, Brinton said. There is accumulating
evidence that exercise provides an independent benefit, but some
studies show a benefit while others don't, she said.
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