U.S. Dietary Guidelines and Cancer Prevention: Your Input Is Needed!

Researchers with expertise in diet and cancer have an opportunity to submit written comments to inform the development of the 2020–2025 edition of the Dietary Guidelines for Americans (DGA). This is a once in five years opportunity for experts to use their research and expertise to inform federal nutrition policies, programs, and communications and ensure that cancer risk is appropriately considered within the context of the relationship between diet and health. This article describes why the DGA are important, how the current edition of the DGA compares with dietary guidelines for cancer prevention, the process to update the DGA for 2020–2025, and how and why cancer researchers should consider submitting comments to inform the update of the DGA.

More than 66,000 incident cancer cases per year in the United States are thought to be attributable to dietary factors alone (1). The evidence that nutritional factors influence cancer risk supports existing cancer prevention recommendations from the American Cancer Society and the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) to consume a mostly plant-based diet rich in whole grains, whole fruit, nonstarchy vegetables and legumes, and low in red and processed meats (2, 3). In addition, excess body weight is a risk factor for at least 13 different cancers (2), and more than 123,000 incident cancer cases per year are estimated to be attributable to excess body weight (1). Thus, recommended healthy dietary patterns are also based on their contribution to weight control. The latest report from WCRF/AICR (2) concluded that sugar-sweetened beverages “convincingly,” and “fast” foods (high in fat, starches or sugars) and a “Western”-style dietary pattern “probably” increase risk of overweight, obesity and weight gain. Likewise, foods high in dietary fiber and a Mediterranean-like dietary pattern “probably” lower the risk of weight gain, overweight, and obesity.

Encouraging cancer prevention through a healthy dietary pattern and lifestyle can be done in a number of ways, including through nutrition education and organizational, community, state, and federal policies governing the availability and provision of healthy foods and nutrition information to inform dietary choices. The DGA is an important tool for promoting dietary patterns and practices that are linked to lower cancer risks.

The DGA is the federal government's official policy on food and nutrition to promote health and reduce the risk of chronic disease, including cancer. The guidelines are jointly developed by the U.S. Departments of Agriculture (USDA) and Health and Human Services (HHS) and updated every five years. The DGA must be based on the best available evidence and provide recommendations for what Americans should eat and drink for optimal health.

By law, the DGA is the cornerstone of all federal government nutrition policies, programs, and messages. A few examples of impactful programs based on the DGA include the National School Lunch Program, which provides 30 million K-12 students with nutritious lunches each school day, the Special Supplemental Nutrition Program for Women, Infants, and Children (better known as WIC), which provides supplemental foods and nutrition education for low-income pregnant and postpartum women, infants, and young children at nutritional risk, and the Supplemental Nutrition Assistance Program Education (SNAP-Ed), an evidence-based program that supports people who receive nutrition assistance in making healthy food choices and helping their food dollars go further. Many state and local governments and private institutions also use the DGA as the evidence base for their nutrition programs, policies, content, and initiatives. For example, workplace nutrition or procurement guidelines are often based on the DGA.

The current DGA, 2015–2020, overlaps considerably with cancer prevention recommendations, specifically by recommending a dietary pattern at an appropriate calorie level that is rich in plant foods (vegetables, legumes, fruit, grains, nuts, and seeds) and low in added sugars. This type of dietary pattern has been consistently associated with a lower risk of colorectal cancer and cancer mortality (3). The dietary patterns suggested in the current DGA include a “healthy US-style eating pattern,” “a Mediterranean-style eating pattern,” and a “vegetarian-style eating pattern”; adapting these healthy patterns to other cultural dietary preferences is encouraged.

There are also notable differences between the DGA and cancer prevention guidelines. For example, the DGA recommends consuming lean meat, without limits on source or quantity, and do not consider potential mechanisms associated with cancer risk (e.g., degree of processing, endogenous nitrosation or formation of carcinogens while cooking meat at high temperatures or over a flame). Processed meat is “convincingly” and red meat is “probably” related to colorectal cancer, according to the WCRF/AICR Third Expert Report, Diet, Nutrition, Physical Activity and Cancer: a Global Perspective (2), consistent with the International Agency for Research on Cancer classification of these foods as Group 1 and Group 2a carcinogens. Although the 2015 Dietary Guidelines Advisory Committee (DGAC), the group of independent experts charged with reviewing the evidence and providing recommendations to HHS and USDA to inform the development of the DGA, recommended limiting these foods, these recommendations were not included in the final guidelines.

Another difference between the current DGA and cancer prevention recommendations is the current DGA recommendation to consume three servings of dairy (or soy) per day. Dairy and calcium are not currently included in overall cancer prevention recommendations due to their complex associations with cancer. For example, the evidence that dairy foods and calcium supplements lower colorectal cancer risk is considered “probable,” while limited-suggestive evidence exists that high dairy and calcium intakes may increase the risk of prostate cancer (3). Therefore, while not making specific suggestions regarding dairy or calcium for overall cancer prevention, the American Cancer Society advises that it may be prudent for men to limit calcium supplementation and not to exceed recommended intake levels of calcium via foods and beverages (3).

The current “eat less” messages from the DGA are expressed in terms of percentage of calories, for example, sugar (≤10% of calories/day), saturated fat (≤10%), and absolute cut-off points for sodium (≤2,300 mg/day), whereas cancer prevention guidelines generally guide the public with food-based recommendations when supported by the evidence (e.g., limit consumption of “fast foods,” sugar- sweetened beverages, and red and processed meats; ref. 2). Current evidence-based guidelines on nutrition and cancer prevention do not directly mention dietary fat, except in the context of reducing consumption of processed foods high in fat, starch, and sugars because of their impact on weight gain (2). Finally, while the current DGA and cancer recommendations are aligned in their message to limit alcohol consumption to no more than one drink per day for women and two drinks per day for men (among those who drink), the evidence that alcohol increases risk of several cancers has strengthened over time, and it is recognized that to prevent cancer, it is best not to drink alcohol (2).

Work is already underway to update the DGA for 2020–2025. Overall, the process involves four key steps, with opportunities for public comment at each point in the process. As the first step, USDA and HHS identified the topics and questions to be examined in the review of the evidence. This is the first time the federal agencies have identified the research questions and limited the scope of the evidence review prior to selection of the group of experts charged with conducting the review. The topic selection process has already been completed, with the draft topics and questions posted for public comment in February–March 2018 and the final topics and questions released in September 2018. The final list of topics and questions is available from https://www.dietaryguidelines.gov/work-under-way/review-science/topics-and-questions-under-review. This list includes several questions both directly and indirectly related to cancer prevention, including:

• What is the relationship between dietary patterns consumed at each stage of life and risk of certain types of cancer?

• What is the relationship between alcohol consumption and risk of certain types of cancer?

• What is the relationship between types of dietary fat consumed at each stage of life and risk of certain types of cancer?

• What is the relationship between dietary patterns consumed at each stage of life and growth, size, body composition, and risk of overweight and obesity?

• What is the relationship between beverage consumption during relevant stages of life and growth, size, body composition, and risk of overweight and obesity?

• What is the relationship between added sugars consumption at each stage of life and growth, size, body composition, and risk of overweight and obesity?

• What is the relationship between the frequency of eating at each stage of life and growth, size, body composition, and risk of overweight and obesity?

The DGAC, an independent committee of experts, is charged with reviewing the evidence and developing conclusions and recommendations on the topics and questions identified. As the second step in the process, USDA and HHS announced the members of the 2020 DGAC in February 2019, following a public call for nominations in September–October 2018. The 2020 DGAC is comprised of 20 independent experts with varied expertise related to diet and health, including the relationship with cancer outcomes.

The third step in the process is the development and publication of a scientific report by the DGAC. The DGAC began this work in March 2019 with a public meeting and is expected to finalize its scientific report by May 2020. The DGAC held an additional public meeting on July 10–11, 2019 and will hold three additional meetings on October 24–25, 2019; Jan 23–24, 2020; and March 12–13, 2020. All meetings will be held in Washington, DC, with the exception of the January 2020 meeting, which will be held in Houston, TX. Opportunities for brief oral public comments are provided at the July 2019 and January 2020 meetings.

Between public meetings, much of the work of the DGAC is being completed through six subcommittees and one cross-cutting working group, the topics of which are Dietary Patterns, Pregnancy and Lactation, Birth to 24 Months, Beverages and Added Sugars, Dietary Fats and Seafood, Frequency of Eating, and Data Analysis, and Food Pattern Modeling. The work of the subcommittees on Dietary Patterns (Chair: Carol Boushey, PhD, MPH, RD, University of Hawaii, Honolulu, HI), Beverages and Added Sugars (Chair: Elizabeth Mayer-Davis, PhD, RD, University of North Carolina at Chapel Hill, Chapel Hill, NC), and Dietary Fats and Seafood (Chair: Linda Snetselaar, PhD, RD, University of Iowa, Iowa City, IA) are likely to be of particular interest to cancer researchers. The work of the subcommittees is supported by USDA and HHS staff, who conduct systematic reviews, food pattern modeling, and data analyses to address the topics and questions identified, with input and oversight by DGAC members. Conclusions will be drawn from this research and assigned a grade of Strong, Moderate, Limited, or Grade Not Assignable based on the strength of the evidence. While the scope of the DGAC's work is limited to the topics and questions already identified, the Committee may choose to focus on specific aspects of the questions and can provide recommendations for further research on other issues. The DGAC will conclude its work with the publication of a scientific report with conclusions and recommendations for USDA and HHS.

Following the publication of the DGAC report, as the final step, USDA and HHS will begin its work to develop the 2020 DGA. At that time, there will be another set of public meetings and opportunity for public comment. Cancer researchers may want to consider submitting comments at that time on the DGAC's scientific report and other research and priority topics that will be important for USDA and HHS to consider in developing the DGA.

In response to direction from Congress, which resulted from pushback from industry and specialty groups displeased with the recommendations of the 2015 DGAC, USDA commissioned the National Academies of Sciences, Engineering, and Medicine (NASEM) to conduct a study and provide recommendations to improve the DGA update process. The NASEM committee recommended five key values to improve the integrity of the process, including enhancing transparency, promoting diversity of expertise and experience, supporting a deliberative process, managing biases and conflicts of interest, and adopting state-of-the-art processes and measures (4). USDA took steps to incorporate some of the recommendations of the NASEM committee in the 2020–2025 DGA update process. For example, to increase transparency, USDA has committed to publishing the DGAC's systematic reviews online for public comment and requiring that they go through a peer review process. Also, the dates of the DGAC public meetings have already been announced, to allow the public to better plan to participate, and there are two opportunities for oral comments at public meetings. However, USDA was unable to address many of the NASEM committee's recommendations - including several of those related to conflicts of interest - for time, resource, legal, privacy or other considerations. The 2020 DGAC is also only relying on systematic reviews conducted by federal researchers to answer its research questions and excluding systematic reviews and meta analyses conducted by researchers and organizations outside the federal government. This is an inefficient departure from the process used by the 2015 DGAC, which utilized existing systematic reviews, meta-analyses, and reports to answer 45 percent of its research questions.

As noted above, the 2020 DGAC will consider evidence on associations of diet with cancer, as did the 2015 DGAC. The associations between diet and overweight/obesity will also be assessed, which has important implications for cancer prevention and survival. Researchers with expertise and interest in these areas can participate in the guidelines process by reviewing and providing comments on the DGAC's research protocols; systematic literature reviews, food pattern modeling, and data analyses; and draft conclusions and recommendations. Researchers may also want to consider sharing results of more recent research/gray literature in a topic area to provide context. Key areas for cancer prevention researchers to address include research on alcohol, dietary patterns, red and processed meats, and types of dietary fat in relation to any of these cancers and all-cause mortality. Note that because evidence on red meat and processed meat will not be reviewed on their own, research that considers their associations in the context of overall dietary patterns may be most useful. Evidence on the relationships of alcohol dose, type and drinking behaviors (e.g., binge drinking) and cancer risk would be important. Data on sugar-sweetened beverages, added sugars, and frequency of eating in relation to overweight/obesity would also be critical. Research published as of mid-2019 will be included in the DGAC's systematic reviews. However, research shared with the Committee for contextual purposes may be published anytime. Note that all comments provided to the DGAC will be made public. While comments will be accepted until May 1, 2020, the DGAC will be best able to utilize comments that are submitted as early as possible in the process.

Following the release of the DGAC's scientific report, there will be a new opportunity for the public to submit comments to inform the development of the DGA. This comment period is expected to be open from approximately May through December 2020. Instructions for submitting comments will be posted at that time at www.dietaryguidelines.gov.

As cancer researchers and experts, we have an obligation to share our knowledge to ensure that the DGA incorporates the most current evidence on prevention of cancer and chronic diseases. We urge those of you with relevant expertise, data, and insights to share them with the committee and participate in this process. For the health of our citizens, is it critical that decisions about dietary and nutrition policies incorporate the best available evidence.

No potential conflicts of interest were disclosed.