This news release attempts to translate preliminary research on plant chemicals into actionable dietary advice. Bad move. Researchers used an innovative screening strategy to cull through 142 natural compounds to identify a combination of three phytochemicals — found in foods such as turmeric, apple peels and red grapes — that inhibited the growth of implanted prostate tumors in mice. Their work is described in the online journal Precision Oncology. But it’s a big leap from the lab table to the dinner table, where the release says that by indulging in certain foods, you can “enjoy the fact that you are eating something that could play a role starving — or even preventing — cancer.” Nowhere does it warn that studies of cell lines or animals don’t prove a human benefit.
Combinations of plant chemicals have become a focus of cancer research, driven by their relative safety, low cost, and wide availability. Lab studies have found substances in plants can reduce inflammation, stimulate the immune system, protect and repair normal cells, and slow the growth of cancer cells, among other things. But research on the effects of these substances to fight specific cancers is still in its infancy, and most experts advise eating a wide variety of fruits and vegetables for better health. Prostate cancer is an area where men feel particularly vulnerable because it’s widespread — about 3 million American men are living with prostate cancer, according to the National Cancer Institute — and there are few actionable steps for prevention. Suggesting a simple solution — such as eating a few specific foods — may give men a false sense of security.
The cost of adding these foods to your diet would be negligible for most people, although taking supplements over long periods could pose a significant cost.
The news release mentions only potential benefits for human beings. There’s no data on how much of these substances might need to be consumed over what period of time and in what quantity to offer cancer protection or tumor shrinkage. A researcher’s comment that “we were able to inhibit tumor growth in mice without toxicity” sheds no meaningful light on these questions.
Also, the news release seems to contradict itself by suggesting that eating a diet containing cancer-fighting substances could offer a benefit, but later quoting a researcher saying, “We only need to increase concentration beyond levels found in a healthy diet for an effect on prostate cancer cells.” This comment seems to suggest people would have to take a supplement in order to get a benefit.
Plant chemicals are generally considered safe, but there’s potential for toxicity if they’re consumed in combination with certain drugs or at high concentrations. There’s added risk for consumers who buy these substances in the form of dietary supplements, which are not tightly regulated by the FDA.
The news release neglects to caution that studying how compounds perform in mouse and human cell lines and in animals doesn’t predict how they will perform in human beings. Extensive human trials are required before any conclusions can be drawn about safety and efficacy.
Furthermore, the release touts the potential benefit of these dietary factors: “These compounds minimize one of the risk factors for cancer, inflammation within the body.” However, it is a huge leap to think even if these compounds could reduce inflammation to a clinically important degree that it would also provide better cancer control.
The release doesn’t engage in overt disease mongering. It describes prostate cancer as “the most common cancer afflicting U.S. men.” That’s true, if you don’t count skin cancer. It’s No. 2 to lung cancer when it comes to causing male deaths.
The news release states that funders include that National Institutes of Health and the University of Texas System, and there were no conflicts of interest that we could find.
While there’s no proven strategy to prevent prostate cancer, there is general advice for reducing overall cancer risk such as quitting smoking, maintaining a healthy weight, exercising, and eating a variety of plant foods. Current treatment options include watchful waiting, active surveillance, hormone therapy, chemotherapy, radiation therapy and surgery. These aren’t mentioned.
Speaking of prevention and treatment in the same release really oversimplifies the issues. There are studies showing that chemoprevention with 5-alpha reductase inhibitors can reduce the risk of prostate cancer, although the FDA will not allow manufacturers to suggest these compounds prevent cancer because these agents were associated with an increased risk for high-grade cancers. Treatment options completely depend upon the stage of the cancer–thus range from conservative management to aggressive attempts at curative therapy to palliative care. The role of these substances in any of these settings is obviously completely unknown.
These foods can be obtained at most grocery stores; availability is not a question. The release could have lent more clarity by telling readers whether supplements are available. For example, resveratrol supplements are available and have been extensively studied for diabetes, obesity, and cardiovascular disease.
The news release provides perspective, stating that the research “uses a novel analytical approach to screen numerous plant-based chemicals instead of testing a single agent as many studies do, discovering specific combinations that shrink prostate cancer tumors.” The claim of novelty seems appropriate regarding the approach to screening.
It also states that the research “demonstrates how the plant-based chemicals work together. Combining ursolic acid with either curcumin or resveratrol prevents cancer cells from gobbling something that they need to grow, glutamine.”
Finally, it acknowledges previous research that has “highlighted the potential therapies found in plants, including chemicals found in foods such as turmeric, apple peels and green tea.”
We rate this as unjustifiable for the over-reaching headline: “Starving prostate cancer with what you eat for dinner.” That’s exacerbated by the lead: “When you dine on curry and baked apples, enjoy the fact that you are eating something that could play a role starving — or even preventing — cancer.”