“Eating well, exercising, and controlling one’s weight are all key in achieving optimal quantity and quality of life among individuals who are diagnosed with cancer.”— Wendy Demark-Wahnefried, PhD, RD
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SINCE 2003, every iteration of the American Cancer Society’s Nutrition Guidelines for Cancer Survivors has advocated for a plant-based diet with ample quantities of whole grains, as well as vegetables and fruits.1-3 This recommendation has been based primarily on data that such foods play in cancer prevention (not necessarily cancer control) and an even greater body of evidence that supports the role of whole grains and fiber in preventing heart disease and other prevalent forms of comorbidity for which cancer survivors are at increased risk.3 A recent study by Song et al,4 reviewed in this issue of The ASCO Post, begins to build a new evidence base that fiber and fiber-rich foods are specifically associated with improved cancer outcomes among cancer survivors.
Data From a Pooled Cohort of Survivors
THIS OBSERVATIONAL investigation is exceptionally strong and is based on a large pooled cohort of 1,575 colorectal cancer survivors identified within the Nurses’ Health and the Health Professionals Follow-up Studies. Data were collected systematically both prediagnosis and postdiagnosis using a validated food frequency questionnaire, and the median length of follow-up was 8 years, during which time 773 deaths were documented (174 from colorectal cancer).
The study compared risk within quartiles of fiber intake. Fortuitously, the referent group had a mean intake of fiber that mirrored that of the general population during the time period of assessment (ie, 14–15 g/d), and the fourth quartile had a mean intake which is well within the range of current guidelines (ie, 21–38 g/d).5 Thus, data from this study are easily generalizable, although it is clear they emanate from a cohort that is much different from the general U.S. population in terms of race, ethnicity, education, and other sociodemographic characteristics. That said, the statistical analysis is careful and controlled for many important covariates. The one exception is the consumption of red and processed meat.
What About Consumption of Red Meat?
IT IS A BIT CURIOUS that the analysis is not controlled for red and processed meat consumption, particularly given the International Agency of Research on Cancer’s determination that there is a consensus of strong evidence that processed meats are carcinogenic as well as probable evidence for red meat—associations that are particularly noteworthy for colorectal cancer.6 Moreover, a prior study by Meyerhardt and colleagues, which examined associations between diet postdiagnosis and mortality among 1,009 patients with stage III colorectal cancer participating in CALGB 89803, found a significant 2- to 3-fold increased risk of both cancer-related and all-cause mortality among those who adhered to a Western diet (for which red meat is a hallmark) but no evidence of protection with a prudent diet (for which whole grains are a hallmark).7
Thus, this analysis by Song and colleagues (many of whom participated on this prior paper) should have controlled for meat consumption to better disentangle whether it really is fiber that affords protection against premature mortality among colorectal cancer survivors or it is the relative absence of red and processed meat that is more the cause. Further analyses and a response by the authors are therefore warranted.
Fiber Intake: Part of the Healthy Lifestyle Puzzle
UNTIL THIS can be resolved, there is no harm and many other health benefits that come from consuming a fiber intake that mirrors current guidelines.5 Fiber intake of 21 to 38 g/d can be accomplished by making deliberate choices to consume whole-grain products (cereals, breads, and pasta) instead of refined grains. Since caramel coloring is often used to fool us into thinking we are eating whole grains when we may not be, patients may need instruction to read labels and look for “whole grains” as the leading ingredient and/or to check the fiber content. Making choices to consume brown rice, quinoa, buckwheat, and other whole grains in lieu of white rice, mashed potatoes, or French fries is another meal strategy that can boost fiber intake substantially. Adherence to the entire set of lifestyle guidelines may bring even more benefit than focusing on just one food group or an isolated food component alone.
The American Cancer Society provides recommendations for both nutrition and physical activity.3 The study by Song et al4 suggests a lower risk of colorectal cancer and all-cause mortality of roughly 30% to 50% by consuming higher amounts of fiber; however, a study by George et al8 among 670 early-stage breast cancer survivors within the Multi-Ethnic Cohort found that women who ate healthier overall diets and who reported regular physical activity had risks for cancer-specific and all-cause mortality that were 89% to 91% lower than those who did not. Thus, eating well, exercising, and controlling one’s weight are all key in achieving optimal quantity and quality of life among individuals who are diagnosed with cancer. ■
Dr. Demark-Wahnefried is Webb Endowed Chair and Professor of Nutrition Sciences, University of Alabama at Birmingham (UAB), and Associate Director, Cancer Prevention and Control, UAB Comprehensive Cancer Center.
DISCLOSURE: Dr. Demark-Wahnefried has received support through an American Cancer Society Clinical Research Professor award.
1. Brown JK, Byers T, Doyle C, et al: Nutrition and physical activity during and after cancer treatment: An American Cancer Society guide for informed choices. CA Cancer J Clin 53:268-291, 2003.
2. Doyle C, Kushi LH, Byers T, et al: Nutrition and physical activity during and after cancer treatment: An American Cancer Society guide for informed choices. CA Cancer J Clin 56:323-353, 2006.
3. Rock CL, Doyle C, Demark-Wahnefried W, et al: Nutrition and physical activity guidelines for cancer survivors. CA Cancer J Clin 62:243-274, 2012.
4. Song M, Wu K, Meyerhardt JA, et al: Fiber intake and survival after colorectal cancer diagnosis. JAMA Oncol. November 2, 2017 (early release online).
5. King DE, Mainous AG 3rd, Lambourne CA: Trends in dietary fiber intake in the United States, 1999-2008. J Acad Nutr Diet 112:642-648, 2012.
6. Bouvard V, Loomis D, Guyton KZ, et al: Carcinogenicity of consumption of red and processed meat. Lancet Oncol 16:1599-1600, 2015.
7. Meyerhardt JA, Niedzwiecki D, Hollis D, et al: Association of dietary patterns with cancer recurrence and survival in patients with stage III colon cancer. JAMA 298:754-764, 2007.
8. George SM, Irwin ML, Smith AW, et al: Postdiagnosis diet quality, the combination of diet quality and recreational physical activity, and prognosis after early-stage breast cancer. Cancer Causes Control 22:589-598, 2011.