The latest research says that by eating just three servings a month of raw broccoli or cabbage a person can reduce their risk of bladder cancer by as much as 40 percent.
The researchers from the Roswell Park Cancer Institute in Buffalo, New York, reached this conclusion after conducting a survey of over 1,000 people where the participants were asked specifically about their intake of cruciferous vegetables.
The researchers were particularly interested in vegetables such as broccoli and cabbage which are rich in compounds called isothiocyanates and are known to lower the cancer risk.
Of the participants 275 people had been diagnosed with bladder cancer and 825 were healthy.
They were asked about pre-diagnosis intakes of raw and cooked vegetables, their cigarette smoking habits, and other risk factors.
The researchers found that the effects were most significant in nonsmokers who ate at least three servings a month and were about 73% less likely to develop bladder cancer than those who smoked and ate less than three servings a month.
Among both smokers and nonsmokers, those who ate this minimal amount of raw veggies had a 40 percent lower risk, but the team did not find the same effect for cooked vegetables.
Dr. Li Tang, who led the study, says cooking can reduce by 60 to 90 percent the isothiocyanates (ITCs) in foods.
ITCs are found in broccoli, cauliflower, kale, turnips, collards, Brussels sprouts, cabbage, radish, turnip and watercress.
When the vegetables are eaten raw isothiocyanates are released which have been shown to neutralise carcinogens and stimulate their secretion.
Studies have shown that isothiocyanates help to prevent lung cancer and esophageal cancer and also lower the risk of other cancers, including gastrointestinal cancer.
The researchers tested the theory using broccoli sprouts in rats who had been engineered to develop bladder cancer.
The rodents were fed a freeze-dried extract of broccoli sprouts and it was found that the more they ate, the less likely they were to develop bladder cancer.
The researchers say the compounds were processed and excreted within 12 hours of feeding which suggests that the compounds are protecting the bladder from the inside.
Lead researcher Dr. Yuesheng Zhang says the bladder is like a storage bag, and cancers in the bladder occur almost entirely along the inner surface, the epithelium, that faces the urine, presumably because this tissue is assaulted all the time by noxious materials in the urine.
In another study from a team at Ohio State University patients with a condition known as Barrett's esophagus which often leads to esophageal cancer, were given black raspberries, also called blackberries or blackcaps, which are also rich in cancer-fighting compounds.
The researchers fed 32 grams of freeze-dried black raspberries to women with Barrett's esophagus and 45 grams to men, every day for a six month period.
They also measured the levels of two compounds in their urine 8-isoprostane and GSTpi -- which indicate whether cancer-causing processes are going on in the body.
The researchers found that 58 percent of patients had marked declines of 8-isoprostane levels, suggesting less damage, and 37 percent had higher levels of GSTpi, which can help interfere with cancer causing damage and which is usually low in patients with Barrett's.
Other studies have also shown that dark-colored berries can reduce the risk of cancer and add to the growing body of research that suggests that fruits and vegetables, especially richly coloured varieties, can reduce the risk of cancer.
The research was presented at the American Association for Cancer Research's Sixth Annual International Conference on Frontiers in Cancer Prevention Research in Philadelphia.
Their findings confirm and strengthen previous research that have linked a high intake of fruits and vegetables with a reduced cancer risk.