Dietary changes don't prevent recurrent polyps, eight-center study shows

April 19, 2000

The Polyp Prevention Trial, one of the largest studies aimed at preventing colon cancer by dietary change, came to an unexpected conclusion:

"The Polyp Prevention Trial provided no evidence that adopting a low-fat, high-fiber fruit- and vegetable-enriched eating plan reduces the incidence of colorectal cancer," according to a report in today's (April 20) issue of the New England Journal of Medicine.

The study, which involved Wake Forest University Baptist Medical Center and seven other centers, tested the effect of diet on recurrence of intestinal polyps. Polyps are considered a precursor of cancer of the colon. The research team had hoped that the study would establish the importance of diet in preventing this cancer.

Instead, for people who already have had polyps, the research team is now recommending regular screening and colonoscopies, according to Elaine Lanza, Ph.D., of the National Cancer Institute, national co-principal investigator.

"This has led us in other directions in preventing colon cancer," said M. Robert Cooper, M.D., principal investigator at Wake Forest and professor of internal medicine (hematology/oncology).

Besides Medical Center patients, Cooper's team recruited participants from private practicing gastroenterologists in Forsyth County, Charlotte, Greensboro, Burlington and Statesville. Half the patients were assigned to the dietary group, half to a control group.

The diet included five to eight servings of fruits and vegetables a day, at least 18 grams of dietary fiber a day for every 1000 calories, and no more than 20 percent of daily calories from fat. The participants on the diet also were assigned a nutritionist for counseling and attended more than 50 hours of individual and group dietary counseling sessions.

The control group got general dietary guidelines from the National Dairy Council -- but no additional nutritional or behavioral help. The trial lasted for four years. Doctors repeated colonoscopies to look for recurring polyps at the end of the first and fourth years.

The participants seem to have followed the diet. The investigators report that the dietary group consumed 9.7 percent fewer calories from fat than the control group and increased their fiber intake by nearly 75 percent. Servings of fruits and vegetables increased by about two-thirds in the intervention group, while control group participants only had a slight increase. Consumption of red meat dropped by about 20 percent in the diet group but only 2.5 percent in the control group. Use of whole grains increased 38 percent in the diet group, but declined in the control group.

Nonetheless, polyps recurred in 39.7 percent of the diet group and 39.5 percent of the control group, a statistical tie.

"We also found no effect of the dietary intervention on either large or advanced lesions," the group reported.

The researchers analyzed a long list of possible explanations, including such considerations that "dietary adherence was less than it appeared," or "the reported changes in intake of fat, fiber and fruits and vegetables were real - but not big enough" or "we intervened too late in life."

They concluded, "The plausibility of several alternative explanations for the…findings argues against concluding definitively that dietary change is ineffective."
-end-
Other centers included Memorial Sloan-Kettering Cancer Center in New York, the State University of New York at Buffalo, the University of Pittsburgh, the University of Utah in Salt Lake City, Walter Reed Army Medical Center in Washington, the VA Medical Center in Hines, Ill., and the Kaiser Foundation Research Institute in Oakland, Calif.
-end-


Wake Forest Baptist Medical Center

Related Cancer Articles from Brightsurf:

New blood cancer treatment works by selectively interfering with cancer cell signalling
University of Alberta scientists have identified the mechanism of action behind a new type of precision cancer drug for blood cancers that is set for human trials, according to research published in Nature Communications.

UCI researchers uncover cancer cell vulnerabilities; may lead to better cancer therapies
A new University of California, Irvine-led study reveals a protein responsible for genetic changes resulting in a variety of cancers, may also be the key to more effective, targeted cancer therapy.

Breast cancer treatment costs highest among young women with metastic cancer
In a fight for their lives, young women, age 18-44, spend double the amount of older women to survive metastatic breast cancer, according to a large statewide study by the University of North Carolina at Chapel Hill.

Cancer mortality continues steady decline, driven by progress against lung cancer
The cancer death rate declined by 29% from 1991 to 2017, including a 2.2% drop from 2016 to 2017, the largest single-year drop in cancer mortality ever reported.

Stress in cervical cancer patients associated with higher risk of cancer-specific mortality
Psychological stress was associated with a higher risk of cancer-specific mortality in women diagnosed with cervical cancer.

Cancer-sniffing dogs 97% accurate in identifying lung cancer, according to study in JAOA
The next step will be to further fractionate the samples based on chemical and physical properties, presenting them back to the dogs until the specific biomarkers for each cancer are identified.

Moffitt Cancer Center researchers identify one way T cell function may fail in cancer
Moffitt Cancer Center researchers have discovered a mechanism by which one type of immune cell, CD8+ T cells, can become dysfunctional, impeding its ability to seek and kill cancer cells.

More cancer survivors, fewer cancer specialists point to challenge in meeting care needs
An aging population, a growing number of cancer survivors, and a projected shortage of cancer care providers will result in a challenge in delivering the care for cancer survivors in the United States if systemic changes are not made.

New cancer vaccine platform a potential tool for efficacious targeted cancer therapy
Researchers at the University of Helsinki have discovered a solution in the form of a cancer vaccine platform for improving the efficacy of oncolytic viruses used in cancer treatment.

American Cancer Society outlines blueprint for cancer control in the 21st century
The American Cancer Society is outlining its vision for cancer control in the decades ahead in a series of articles that forms the basis of a national cancer control plan.

Read More: Cancer News and Cancer Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.