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Draft Statement: Evidence Connecting Diet to Colorectal, Breast Cancer Stronger Than Links to Lung, Prostate
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If you mother told you, “Eat your vegetables,” she knew intuitively what science continues to affirm.
The 2015 US Dietary Guidelines Advisory Committee (DGAC), charged with making recommendations to update the nation’s policies for healthy eating, held its fourth meeting on July 16 and 17, 2014, in Bethesda, Maryland. During the meeting, a key subcommittee tasked with reviewing recent evidence on how dietary patterns affect health developed draft language on the relationships between what Americans eat and 4 major cancers—breast, colorectal, prostate, and lung—as well as chronic conditions such as type 2 diabetes mellitus (T2DM) and obesity. This is the first time that the DGAC’s report will include recommendations on the connections between diet and cancer.1,3
Chaired by Barbara Millen, DrPH, RD, of Millennium Prevention in Westwood, Massachusetts, the 2015 DGAC consists of 15 scientists specializing in nutrition, cancer prevention, public health, and other fields who were appointed in spring 2013 to offer recommendations to the US secretaries of Health and Human Services (HHS) and Agriculture (USDA). As outlined by Congress, the process takes place every 5 years, with management rotating between HHS and USDA.2,3
DGAC’s work remains in draft form until the final report goes to the secretaries, who then review it alongside comments from the public—which have been received in-person and online—as well the many “stakeholders,” which include lobbyists for the food industry, some of whom have already appeared before DGAC during the public comment sessions.3
The final policy is released as Dietary Guidelines for Americans, a document that affects everything from the composition of school lunches, to the makeup of meals fed to the military, to the allotments that go into the Supplemental Nutrition Assistance Program. Fallout from the guidelines sometimes stirs controversy. The work of the 2015 DGAC continues as the National School Boards Association and other groups lobby Congress for relief from the Healthy Hunger-Free Kids Act of 2010, which revamped the rules governing what school districts receiving federal funds can serve in school lunches.4,5
In prior remarks and in her opening address to the committee on July 16, Millen discussed the committee’s assignment of examining how the improvements to the American diet can reduce chronic disease. The committee, she said, “is charged with providing technical assistance on how food, nutrition, and physical activity can do 2 things: promote the health of the US population and help reduce the burden of chronic disease and other lifestyle-related problems, and also develop recommendations
and best methods and practices, at the individual and population level.”1
Millen said the emphasis on “dietary patterns” allows for several things: a review of how Americans eat now, a review of the evidence of what dietary patterns are associated with chronic disease and with cancers, and an analysis of “what works,” which will provide practical recommendations for healthcare and public health officials.
The first day of the July meeting featured presentations from Frank Hu, MD, PhD, MPH, of the Harvard School of Public Health, and Steven Clinton, MD, PhD, of the Ohio State University. Hu presented draft language on the relationship between dietary patterns and CVD, body weight/obesity, and T2DM, while Clinton presented language on the relationships between dietary patterns and 4 major cancers that account for half of the cancer incidence in the United States: lung cancer, prostate cancer in men, breast cancer in women, and colorectal cancer.
As Hu and Clinton outlined, and as committee members noted, there was a high degree of consistency across the evidence base when examining what dietary patterns were connected with lower or higher incidence of chronic disease and with cancer. Among the 4 major cancers, evidence showed the strongest links between dietary patterns and colorectal cancer, and moderate evidence involving dietary patterns and post menopausal breast cancer.
More illuminating, however, was the high level of consistency in the draft recommendations, whether they involved major cancers or chronic diseases. (For draft conclusions in colorectal and breast cancer, see the Table.) In summary, the committee draft conclusions find links between better health outcomes and:
• A diet high in fruits, vegetables, and whole grains
• A diet with regular amounts of fish, legumes, and low-fat dairy. Alcohol can be consumed in moderation
• A diet low in sugar-sweetened beverages, red and processed meats, refined grains, and saturated fats
The consensus in the draft statements emerged from a rigorous process for all 4 major cancers and for the chronic diseases. Clinton said the literature review for dietary patterns and cancer covered the period from January 2000 through 2014, taking in a total of 82 articles: 25 involving breast cancer, 22 involving colorectal cancer, 4 on lung cancer, and 7 on prostate cancer.
At the outset, Clinton explained the limitations involved in the committee’s review. “Despite the expanding number of available studies regarding dietary patterns and cancer risk, the portfolio of quality studies remains modest and employs a wide methodology in study design, dietary pattern assessment, and statistical approaches,” he said.
Indeed, the committee was unable to draw any conclusions about links between dietary patterns and prostate cancer, due to the disease’s complex epidemiology and a variety of other factors. In lung cancer, there is some evidence that dietary patterns similar to those that affect breast cancer outcomes are in play, but it is very limited. And regarding lung cancer, Clinton said, additional research is needed to understand the interplay between diet and tobacco use, including the age when tobacco use starts and the type of tobacco involved.
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More research is also needed, Clinton said, to understand the role of dietary patterns in premenopausal breast cancer. References
1. HHS. 2015 Dietary Guidelines Advisory Committee, Fourth Meeting, Day 1. http://videocast.nih.gov/summary.asp?Live=14230&bhcp=1. Webcast July 16, 2014. Accessed August 30, 2014.
2. 2015 Dietary Guidelines Advisory Committee. 2015 DGAC members. http://www.health.gov/dietaryguidelines/2015-binder/2015/membership.aspx. Accessed August 31, 2014.
3. Caffrey MK. Dietary patterns, and effect on population health, get attention from panel. Am J Manag Care. 2014;20(SP4):SP111-SP112.
4. Evich HB. Michelle Obama fights to defend school lunch changes. Politico. http://www.politico.com/story/2014/05/michelle-obama-school-lunchnutrition-changes 107121.html. Published May 27, 2014. Accessed September 1, 2014.
5. Gentzel TJ. Making school nutrition a political issue has distorted reality in our cafeterias. The Huffington Post. www.huffingtonpost.com/thomasj- gentzel/making-school-nutrition-a_b_5630823. html. Published July 29, 2014. Accessed September 1, 2014.
