= Full article availableIt used to be that a cancer diagnosis was a death knell. But today, there are 9 million people in the US—roughly three in every 100—who have had cancer and survived. And many of them look to nutrition—eating specific foods, taking supplements, or following certain diet regimens—as a hedge against future illness.
Fortunately, scientists have made inroads on the nutrition front for survivors. Following, a rundown of different recommendations they’ve established thus far.
Losing excess weight gives an edge
Oncology researchers know that carrying around too many extra pounds can increase cancer risk in the first place. Now, they’re beginning to collect evidence that excess weight may potentially hurt the chances of survival after some cancers. In the case of breast cancer, for which there’s the most data, there have been “numerous studies” that have linked being overweight at the time of diagnosis with recurrent disease, decreased survival, or both, says Wendy Demark-Wahnefried, PhD, RD, a cancer researcher at Duke University Medical Center. A handful of studies have shown, in addition, that weight gain after diagnosis is linked with increased recurrence as well, she comments, though their data “are not as consistent.”
Why the connection between excess weight and cancer recurrence? It could be that too much fat tissue raises levels of estrogen, which plays a role in the development of certain breast cancers. The more a woman is exposed to estrogen over her lifetime, it’s believed, the more likely she may be to develop a breast tumor. Extra pounds have also been linked with increased levels of the hormone insulin and other so-called “growth factors” that may promote tumor growth, as well as with impairment of the immune system.
Pondering soy and flax
Soy has been touted for prevention of hormone-sensitive cancers, such as those of the breast and prostate, for a number of years. In the case of breast cancer, the theory has been that plant estrogens in soy called isoflavones are similar enough to human estrogen that they can fit comfortably onto estrogen receptors in breast tissue and thereby block the more potent human version of the hormone from binding. That’s important because human estrogen can spur the production of breast cancer cells. In prostate cancer, plant estrogens could theoretically reduce production of the male hormone testosterone, which can hasten prostate cancer progression.
Cancer survivors, naturally, want to know whether soy might prevent recurrence. For survivors of prostate cancer, it may be worth a try. A new review of evidence by experts at Harvard Medical School, the National Institutes of Health, and two Canadian institutions notes that while studies haven’t reached any firm conclusions yet, the plant estrogens in soy might possibly have benefit in delaying prostate cancer progression—and it’s unlikely that men with the disease would risk anything by including it in their diets. That is, “it generally appears reasonable to accept the consumption of soy supplements or soy foods by patients with prostate cancer,” says lead author Wendy Weiger, MD, PhD.
But the same report specifically discourages consumption of soy supplements by women with endometrial cancer or by breast cancer patients who have estrogen receptor-positive tumors or are taking the anti-estrogen drug tamoxifen. The same substances in soy that can compete with estrogen may also enhance the hormone’s growth-promoting effects on certain breast cancer cells. In other words, instead of acting against human estrogens, components of soy, when concentrated in supplements, may in certain circumstances act with them to promote cancer progression.
Soy foods present more of a gray area. In the face of the evidence, many experts believe it’s probably okay for a woman with breast cancer to continue eating soy-based foods here and there if she has done so in the past. They’re not so sure, however, about the benefits of adding a lot of soy foods to the diet of a woman who already has had breast cancer or is at high risk. The American Institute for Cancer Re-search, for instance, cautions that “women who are at high risk for breast cancer, take tamoxifen, or have been diagnosed with estrogen receptor-positive breast cancer may want to limit themselves to no more than a few servings per week.” The advice is even stronger on soy supplements and powders that provide concentrated doses of isoflavones: breast cancer survivors should steer clear of them.
With flaxseed, which contains plant estrogens called lignans, “it’s much like the debate with soy,” notes Duke University’s Dr. Demark-Wahnefried. Research says taking flaxseed “may be protective, but in certain instances it may also enhance proliferation rates. It’s disconcerting, and we have to be careful.”
Because researchers haven’t nailed down exactly how flaxseed’s lignans affect cancer growth or cancer-fighting drugs like tamoxifen, Lilian Thomp-son, PhD, a University of Toronto researcher who has studied flaxseed’s effects on disease for about 15 years, recommends that women taking tamoxifen or other anti-estrogenic drugs should not consume flaxseed. (Flaxseed oil, which does not naturally contain lignans, is fine—as long as the manufacturer hasn’t added them in.)
The American Institute for Cancer Research concurs. While flaxseed appears to be safe for women who have never had breast cancer, it says, women undergoing breast cancer treatment should not use flaxseed until more information becomes available.
Out-there strategies
There are many more unproven than proven dietary and lifestyle strategies for avoiding cancer recurrence. Unfortunately, a lot of cancer survivors, eager for protection, aren’t waiting for scientists to agree on whether they’re worth following. The American Institute for Cancer Research reports that as many as 80 percent of cancer survivors are using unproven dietary supplements or regimens as a hedge against recurrence. There’s a “very strong desire among people to take some control of their health,” says oncologist Steven K. Clinton, MD, PhD, of Ohio State University. But “many people are sold products based on misleading claims and sensational marketing,” he says. There’s “little benefit, and more risk.”
What they’re putting their faith in can be risky indeed. Consider what happened with PC-SPES, an herbal formula taken by many prostate cancer survivors in hopes of slowing the disease. It “became popular 4 or 5 years ago,” Dr. Clinton says. “Tens of thousands of people were buying it” at a cost of “several hundred dollars a month.” Clinical trials had suggested some benefits, he notes. But then, complications cropped up—frequent blood clots, as well as coagulation problems in some people taking blood thinners.
Why? “The provider of the herbal product was spiking it with prescription medicines,” he explains—the blood-thinning drug Coumadin, as well as estrogen, which was causing the blood clots. “They deceived the public and put people at risk.…You have to be careful and realize that supplement purveyors are not regulated like drug companies,” he warns, pointing out that lack of regulation allows for easy adulteration of the products.
Other cancer “treatments” with potential for harm include coffee enemas, which can cause serious complications like intestinal perforation and major infections, as well as strict eating regimens like macrobiotics. That diet can lead to severe malnutrition in the form of weight loss and muscle wasting along with deficiencies in calcium, iron, vitamin B12, riboflavin, and other nutrients. Even a benign-sounding raw food diet, promoted by some as a cancer cure, can cause harm if it convinces people with cancer to forego medically proven treatments.
Better to stick with the dietary strategies that, while not yet fully proven for cancer survivors, at least have great weight behind them as cancer preventives in the first place and can’t do any harm: eating a plant-based diet rich in all kinds of fruits, vegetables, and whole grains; limiting alcohol, salt, and fatty foods; keeping weight in check; and exercising regularly.
“Research has focused on a cure first,” explains Dr. Clinton. There’s still a ways to go on preventing recurrence. Still, he comments, “the good news is that there are more cancer survivors.…We didn’t have this problem before we could cure them.”
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