07 Dec 2007

Veggies vs. cancer

Your local farmer's market might hold the key to cancer prevention, since new research shows that black raspberries, broccoli sprouts and some raw vegetables reduce the risk of oesophageal and bladder cancers.

Fruits and vegetables have long been known to help reduce the risk of certain cancers. Based on prior research, the American Cancer Society recommends eating five servings of fruits and vegetables daily.

In one study, Ohio State University researchers found black raspberries may protect against oesophageal cancer by reducing the oxidative stress that results from Barrett's oesophagus, a precancerous condition usually caused by gastroesophageal reflux disease. The oesophagus is a long tube that connects the throat to the stomach. Reflux disease causes stomach acid to continually splash back up into the oesophagus.

"Specifically in the case of Barrett's patients, reflux of the stomach and bile acid contribute to ongoing oxidative damage. Thus, our hypothesis is that feeding a food that is high in potential protective constituents, such as antioxidants, vitamins, minerals and other phyto-chemicals, may help restore the oxidative balance," lead researcher Laura Kresty said.

People with Barrett's oesophagus typically are 30 to 40 times more likely to develop oesophageal cancer, which has a poor five-year survival rate of 15 percent.

The team gave 32 grams to 45 grams of black raspberries daily for six months to 20 patients with Barrett's oesophagus. They analyzed changes in blood, urine and tissue before, during and after the treatment, and found lower levels of some of the chemical markers of oxidative stress in both urine and tissue samples.

Black raspberries previously have been shown to reduce the risk of oral, oesophageal and colon cancer in animal models, according to the researchers, who called for further study in humans.

"It couldn't hurt"
Dietician Wendy Demark-Wahnefried, a professor of behavioural science at M.D. Anderson Cancer Centre at the University of Texas in Houston, said she would feel comfortable advising people with Barrett's to eat black raspberries. "It couldn't hurt," she said, but added that further studies need to find out if the berries really do prevent cancer.

In other research broccoli sprouts and cruciferous vegetables both showed promise in the fight against bladder cancer, according to two separate teams from the Roswell Park Cancer Institute in Buffalo, N.Y.

Using a rat model, a team lead by Dr Yuesheng Zhang, a professor of oncology, demonstrated that a broccoli sprout extract reduced bladder cancer in rats by 70 percent.

"Our present study shows that broccoli sprout extracts fed to rats in the diet inhibits bladder cancer development induced by a carcinogen. We don't yet know if the extracts inhibit the growth of an existing bladder cancer," said Zhang, who explained that broccoli sprouts are a rich source of a well-known cancer preventive agent known as sulforaphane.

"We next plan to find out if broccoli sprout extracts can fight bladder cancer in humans," Zhang noted.

Reduced cancer risk
A second team at the institute found that people who ate three or more servings of raw, cruciferous vegetables per month reduced their risk of bladder cancer by 40 percent. Cruciferous vegetables include broccoli, cabbage and cauliflower.

The team analyzed the dietary habits of 275 people with early bladder cancer and 825 people who were cancer-free. The researchers specifically asked how many servings of raw or cooked cruciferous vegetables they ate before their diagnosis and whether they smoked.

Analysis of the data showed that the more raw, cruciferous vegetables people ate, the lower their risk of bladder cancer. In comparison to people who smoked and ate fewer than three servings of raw vegetables a day, non-smokers eating at least three servings of cruciferous vegetables daily were 73 percent less likely to develop bladder cancer.

"In our study, we do find intake of raw cruciferous vegetables showed risk reduction of bladder cancer in smokers, and even the heavier smokers," said lead researcher Li Tang.

The researchers stressed that the benefits are derived from raw cruciferous vegetables, giving coleslaw the edge over cabbage soup when it comes to cancer prevention.

More colour, more cancer-fighting antioxidants
"This confirms that there are a variety of compounds within fruits and vegetables that contribute to reducing the risk of cancer. Research like these studies contribute to our knowledge about what the impact of specific nutrients may be on specific types of cancer," said Colleen Doyle, director of nutrition and physical activity for the American Cancer Society. "Cooking leaches out some nutrients but makes others more absorbable. Until we know more in this regard, the bottom-line message for consumers is eat at least five servings of fruits and vegetables each day, raw and/or lightly cooked. Focus on those with the most colour, since, in general, fruit and vegetables with the most colour have the most cancer-fighting antioxidants and phytochemicals."

"Surveys we've done indicate many people don't think they have control over their cancer risk, but studies clearly indicate they do. For the majority of people who don't smoke, watching their weight, being more active and eating a healthy diet are the most important ways to reduce cancer risk," Doyle said. - (Madeline Vann/HealthDay News)