Final proof that dietary components like green tea, curry spice or wine can fight cancer in humans and not just laboratory test tubes remains elusive, but researchers are full of hope for the unconventional treatments.
"I believe that 50 years from now there will be a sub-specialty of medicine called cancer prevention doctors,' Dr Allan Conney, professor of cancer and leukaemia at New Jersey's Rutgers University, said on Wednesday.
"These doctors will be able to identify cancer risk factors for each individual and, along with pharmacists, prescribe drugs, diet or lifestyle changes." Speaking in San Francisco at a meeting of the American Association for Cancer Research, Conney said studies now underway on the anti-cancer effects of green tea, turmeric and other agents will eventually add years to the human life span.
But he noted that the leap from testing these theories in the lab to testing them in humans remains as difficult as ever. "Results of trials in humans have been inconsistent. There is a need for much more carefully controlled studies," Conney said.
One solution is to measure the body's processing of a particular dietary component, rather than rely on patients to report their actions, he suggested.
One study using this approach found that drinking green tea cuts in half the chance of cancer of the stomach or oesophagus in Chinese men at high risk for the disease.
Several studies have suggested green tea might help ward off heart disease and certain cancers, possibly due to potent antioxidant substances called polyphenols, which are also found in foods like grapes and wine. Antioxidants help protect the body from cell-damaging forms of oxygen that occur naturally in the body and are believed to contribute to a range of diseases.
"This is the first human evidence that tea polyphenols reduce the risk of oesophageal cancer," said Dr Can-Lan Sun, a researcher at the University of Southern California in Los Angeles and the study's lead author.
The study, which followed middle-aged or older men in Shanghai, China, for between four and 12 years, found that men whose urine had high levels of a particular tea polyphenol - a measurement of tea consumption - had a lower risk of both stomach and oesophagus cancers.
But another study, conducted at the Mayo Clinic in Rochester, Minnesota, found that green tea was not effective as a treatment for men who already have advanced prostate cancer. Only one patient of the 42 evaluated in the mid-stage trial saw his cancer improve, and the response did not last.
After one month of treatment - the study was designed to last four months - many patients dropped out because their cancer got worse and because of caffeine-related side effects.
Dr Aminah Jatoi, lead investigator and assistant professor at the clinic's oncology department, said the study used a high dose - liquid tea concentrate equivalent to 12 cups a day - because the researchers did not want to be accused of short-changing these very sick patients.
Preliminary results from another study, this one in test tubes, showed that a component of the popular Indian spice turmeric may also help fight cancer.
Researchers from Detroit's Henry Ford Health System found that the active ingredient in turmeric, called curcumin, can boost the cancer-fighting power of treatment with a naturally occurring molecule, called TRAIL, that helps kill cancer cells.
Subhash Gautam, a researcher at the Henry Ford Health System, said the combination treatment would next be tested in mice.
There is evidence that turmeric has anti-inflammatory and antioxidant properties and it may work against cancer cells by sensitising them to other drugs, he said.
In another study, researchers at Germany's University of Ulm, found that combining TRAIL with resveratrol, an antioxidant found in red wine, killed cancer cells and slowed the growth of human tumours implanted in mice.