October 2018 Issue
New Landmark Report on Cancer Prevention — What It Means for Messages on Healthful Eating
By Karen Collins, MS, RDN, CDN, FAND
Vol. 20, No. 10, P. 36
Dietitians increasingly are fielding questions from clients and patients about news headlines on reducing cancer risk, and often from individuals in non-oncology settings.
Now RDs have greater certainty than ever before concerning the answers to various questions. The new landmark report from the American Institute for Cancer Research (AICR) and World Cancer Research Fund (WCRF) recently was released and is considered an important tool in the toolbox for all dietitians. This article examines the updated recommendations for lowering cancer risk from the organizations' Third Expert Report, "Diet, Nutrition, Physical Activity and Cancer: A Global Perspective,"1 and discusses how to develop talking points and evidence-based messages.
Those who are familiar with the previous AICR/WCRF recommendations to reduce cancer risk may note that the new recommendations haven't changed dramatically. An important distinction, however, is seen in looking at the underpinnings of the report, much like reviewing the specs of a new computer.
Stronger evidence: Whereas the best available evidence for many nutrients and cancers previously included a mix of case-control studies and scientifically stronger prospective cohort studies, the evidence base in the new report rests largely on cohort studies and randomized controlled trials. Mechanistic studies also are considered, since the criteria needed to support a recommendation include not only a strong association in epidemiologic research but also plausible evidence of a biological mechanism that could explain the association.
This has led to more emphasis on the importance of some recommendations, such as regular physical activity and limits on alcohol. In a few cases, it led to recognition that the evidence may not be as strong as researchers once thought, resulting, for example, in no longer including a recommendation specifically focused on salt or sodium. Growing recognition of the complexity of cancer also is reflected in the new report. Different types of cancers—of the breast, esophagus, and stomach, for example—may be influenced by different lifestyle choices.
More emphasis on overall eating patterns: Reflecting advances in research, focus on individual foods or nutrients has become less pronounced than the emphasis on overall dietary patterns, weight and weight gain, and a lifestyle with regular physical activity and less sedentary time.
How the Report Was Created
The Continuous Update Project (CUP) is an ongoing program that gathers and analyzes research from around the world on how diet, nutrition, and physical activity affect cancer risk and survival. WCRF International leads the effort in partnership with the AICR. A team of scientists at Imperial College London gathers the best available scientific research and conducts systematic literature reviews (SLRs). These SLRs are then peer-reviewed by outside reviewers. Currently, the CUP database includes 18 SLRs covering 17 different cancers, with one on breast cancer survivors.
An independent panel of researchers, the CUP Expert Panel, then evaluates the strength of the evidence for each diet, weight, or physical activity factor related to each cancer type. Specific criteria are used to classify evidence as strong (either "convincing" or "probable"), limited (either "limited – suggestive" or "limited – no conclusion"), or "substantial effect on risk unlikely."
The Third Expert Report summarizes and synthesizes the latest findings from the CUP. In addition, the report provides updated cancer prevention recommendations developed by the expert panel, focusing on evidence categorized as strong. Goals are provided with each recommendation that aim to identify achievable steps that can be expected to result in true health gains.
Stephen Hursting, PhD, a professor in the department of nutrition at the University of North Carolina at Chapel Hill served on the CUP Expert Panel. "Nobody else does this amount of work across all of these lifestyle exposures," he says. "This new report provides the most complete picture available for the impact of these factors on cancer risk."2
The Recommendations and the Science Behind Them
1. Be a Healthy Weight
Keep your weight within the healthy range and avoid weight gain in adult life.
This recommendation heads the list because evidence that greater adiposity is a cause of many cancers is particularly strong.3 The new report links overweight and obesity to increased risk of at least 12 cancers.1
Excess body fat appears to increase cancer risk through several potential effects.4-6 Adipose tissue is the primary site of estrogen synthesis in postmenopausal women, and obesity's link with estrogen-sensitive cancers likely involves increased levels of bioavailable sex steroid hormones. Obesity also is associated with elevated levels of insulin, insulinlike growth factors (especially IGF-1), and leptin, which can promote the growth of cancer cells. Adipose tissue also is the source of cytokines that, along with reduced levels of the anti-inflammatory hormone adiponectin, can lead to chronic low-grade inflammation, one of the hallmark characteristics enabling cancer development.
• Adult weight gain is associated with unhealthy metabolic changes and increased risk of some cancers.3,7 Since long-term maintenance of weight loss can be challenging for many people, avoiding weight gain can be an important goal for people currently at a healthy weight and those who are overweight.
• For people with overweight or obesity, even modest weight loss could potentially reduce cancer risk. Current research is limited but demonstrates that intentional weight loss can produce clinically significant changes in biomarkers of cancer risk.3,6,8
2. Be Physically Active
Be physically active as part of everyday life—walk more and sit less.
Physical activity seems to reduce cancer risk both directly and through assistance in maintaining a healthy weight.9 Several mechanisms could account for its protective effect, including improved levels of insulin and sex steroid hormones, and better immune function.1,10,11 Independent of the amount of moderate or vigorous activity, greater sedentary time may increase risk of several cancers.1,10,11
• Make physical activity part of everyday life, regardless of body weight. Adults should get at least 150 minutes of moderate activity, or 75 minutes of vigorous activity, every week.1,11 As fitness improves, increase the amount for greater protection.
• Physical activity directly reduces risk of at least three cancers; indirectly, through its help in reaching and maintaining a healthy weight, it protects against many more.
• Limit the amount of time spent sitting for extended periods, and take regular breaks.
3. Eat a Diet Rich in Whole Grains, Vegetables, Fruit, and Beans
Make whole grains, vegetables, fruit, and pulses (legumes) such as beans and lentils a major part of your usual daily diet.
Relatively unprocessed plant foods provide phytochemicals, vitamins, and minerals that, as part of the whole food, may provide protective effects on carcinogen metabolism, inflammation, DNA integrity, cell cycle regulation, hormone levels, and the gut microbiome.1,12-16 Foods that contain dietary fiber, and whole grains specifically, seem to protect against colorectal cancer.1
The association of vegetables and fruits with lower cancer risk was supported more strongly by earlier case-control studies, with evidence from prospective cohort studies less consistent. But the expert panel concluded that a pattern of protective association is consistent and evidence is strong that greater consumption probably protects against several cancers. Rather than focus on particular nutrients in plant foods, current evidence suggests focus on a dietary pattern in which a variety of plant foods predominate.
• Include five or more standard servings of nonstarchy vegetables and fruits each day. (One serving here is equal to about 1/2 cup of most raw or cooked vegetables or fruits, or 1 cup of raw leafy vegetables, or 1/4 cup of dried fruit). This meets the recommendations to reduce cancer risk. Working toward even larger amounts likely helps further decrease risk of cancer and heart disease and may be helpful in achieving a calorie level that supports a healthy weight.
• Cancer-protective effects of whole grains likely involve not only dietary fiber but also their nutrient and phytochemical content.17 To avoid excess calories, whole grains should be substituted for, not added to, refined grains.
• Legumes provide several forms of dietary fiber that can act in multiple ways to lower risk, as well as valuable nutrients and phytochemicals.1,17 They offer a low-cost protein source that can help make a cancer-protective diet more budget friendly.
4. Limit Consumption of "Fast Foods" and Other Processed Foods High in Fat, Starches, or Sugars
Limiting these foods helps control calorie intake and maintain a healthy weight.
This recommendation isn't targeting a direct effect of these foods on cancer risk, but the major effects of adiposity. Studies show they promote weight gain, overweight, and obesity when consumed frequently or in large portions.1,18,19
• Limit frequency and portion of traditional "fast foods" and other processed foods high in fat, added sugars, and refined grains. Replace them with vegetables, fruits, and relatively unprocessed grains, which improve overall diet quality and are less likely to promote weight gain.20-22
• Evidence doesn't support avoidance of all high-fat foods for weight control or to lower cancer risk, so learn to include small servings of some oils, nuts, and seeds within a healthful eating pattern.1,20,22
5. Limit Consumption of Red and Processed Meat
Eat no more than moderate amounts of red meat, such as beef, pork, and lamb. Eat little, if any, processed meat.
Processed meats are those preserved by smoking, curing, salting, or the addition of chemical preservatives. Common examples include bacon, ham, sausage, hot dogs, and salami.
Excess consumption of red and processed meat raises risk of colorectal cancer.1,23 Red meat is higher than poultry or seafood in heme iron, which can lead to production of free radicals that damage DNA, and promotes formation of N-nitroso compounds (NOCs) within the gut.24,25 NOCs also form when nitrites used to preserve meat combine with amines from amino acids, which can occur during meat processing or in the stomach. Another source of cancer risk from red and processed meats stems from cooking at high temperatures or over open flames, producing carcinogenic heterocyclic amines and polycyclic aromatic hydrocarbons, respectively.14,24 However, the latter effect isn't unique to red and processed meats, so it doesn't explain the difference in risk compared with poultry and seafood.
• People who eat red meat should keep amounts within moderation, which the new expert report defines as no more than 12 to 18 oz per week.1
• Processed meat poses greater cancer risk than unprocessed red meat and thus warrants more caution. Research doesn't yet show whether some forms of processed meat pose more risk than others, so for now, it's recommended that consumption of all forms of processed meat be minimized.
6. Limit Consumption of Sugar-Sweetened Drinks
Drink mostly water and unsweetened drinks.
This is another recommendation that isn't associated with a direct effect on cancer risk but reduces cancer risk by avoiding weight gain and the tendency for overweight and obesity.1,26
• Drink water and other unsweetened drinks such as unsweetened tea or coffee as primary beverage choices.
7. Limit Alcohol Consumption
For cancer prevention, it's best not to drink alcohol.
Evidence is now stronger than ever that alcohol is a cause of several different cancers. Ethanol is a Group 1 human carcinogen.27 Its metabolism generates acetaldehyde, another human carcinogen.28 Research suggests that DNA damage could come from acetaldehyde itself, as well as from free radicals produced during alcohol metabolism.1,27 Ethanol also may increase cancer risk by acting as a solvent, enhancing penetration of dietary carcinogens into cells, and by increasing circulating levels of estrogen, an established risk factor for breast cancer.1,27
• If you drink alcohol of any type, limit intake to no more than two drinks per day for men, and one drink per day for women. Not drinking alcohol is better for cancer prevention. (For more information, read "Alcohol Consumption and Cancer Risk — The Other Side of a Health Halo," in the April 2018 issue of Today's Dietitian.)
• Risk of some cancers seems to increase mainly with alcohol beyond moderation. However, even amounts classified as moderate pose a small increase for some cancers, such as breast cancer.1,29,30
• Despite laboratory findings on resveratrol, a phytochemical found in red wine, human research doesn't support red wine as different from other alcoholic beverages in relationship to cancer risk.27,29
8. Don't Use Supplements for Cancer Prevention
Aim to meet nutritional needs through diet alone.
Dietary supplements may fill a specific nutrient gap for some people. However, human research translating benefits seen in laboratory studies doesn't support dietary supplements as an effective strategy to reduce cancer risk.1,31,32 Mounting evidence of U- or J-shaped dose-response curves for nutrients indicates that too little and too much may both pose health risks.
• Forget the concept "If some is good, more is better." Achievable amounts of nutrient-rich foods, swapped as replacements for foods low in nutrients, are enough to make a difference in cancer risk.
• Obtaining nutrients and other compounds from food bring a whole range of protectors that can act in multiple ways against cancer development.
9. For Mothers: Breast-Feed Your Baby, If You Can
Breast-feeding is good for both mother and baby.
Breast-feeding lowers a mother's risk of both pre- and postmenopausal breast cancer, apparently through effects on lifetime estrogen exposure and effects on cells within the breast.1 Babies benefit from the known immune and other health benefits of breast-feeding, and it also may reduce long-term cancer risk by decreasing risk of obesity.33 Exclusive breast-feeding for the first six months—giving babies no other nourishment, including water, except for vitamin drops where needed—is consistent with other infant feeding recommendations.34,35
• Breast-feeding is good for mother and baby.
• The longer women breast-feed their babies, the greater their protection against cancer.
10. After a Cancer Diagnosis: Follow Our Recommendations, If You Can
Check with your health professional to determine what's right for you.
People who have been diagnosed with cancer have diverse nutrition issues—both during and after cancer treatment—that can be important in the short term and for long-term survival.
• People who have been diagnosed with cancer should have access, as soon as possible, to nutrition care and guidance on physical activity from trained health professionals who can take into account their personal situations and circumstances.
• After the acute stage of treatment, cancer survivors are advised to follow the recommendations for cancer prevention, if possible, and unless otherwise advised, by a qualified health professional.
The Big Picture
The message from this new landmark report is to use these recommendations as a blueprint for creating a lifestyle that, including avoidance of tobacco and excess sun, can prevent about 40% of cancers. Studies using a score to identify how closely people come to meeting the previous AICR/WCRF recommendations show that the closer people come to the whole package of recommendations, the more powerfully they protect themselves against cancer.36-38 Dietitians have a vital role in helping people focus on these priorities and put them into action.
— Karen Collins, MS, RDN, CDN, FAND, is a nutrition consultant specializing in cancer prevention and cardiometabolic health, and is nutrition advisor to the American Institute for Cancer Research.
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2. Hursting S. Personal e-mail interview. August 6, 2018.
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22. Mozaffarian D. Dietary and policy priorities for cardiovascular disease, diabetes, and obesity: a comprehensive review. Circulation. 2016;133(2):187-225.
23. World Health Organization, International Agency for Research on Cancer. IARC monographs: consumption of red meat and processed meat: volume 114. https://monographs.iarc.fr/wp-content/uploads/2018/06/mono114.pdf. Published March 2018.
24. Hammerling U, Bergman Laurila J, Grafström R, Ilbäck N-G. Consumption of red/processed meat and colorectal carcinoma: possible mechanisms underlying the significant association. Crit Rev Food Sci Nutr. 2016;56(4):614-634.
25. Fonseca-Nunes A, Jakszyn P, Agudo A. Iron and cancer risk — a systematic review and meta-analysis of the epidemiological evidence. Cancer Epidemiol Biomarkers Prev. 2014;23(1):12-31.
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38. Nomura SJ, Inoue-Choi M, Lazovich D, Robien K. WCRF/AICR recommendation adherence and breast cancer incidence among postmenopausal women with and without non-modifiable risk factors. Int J Cancer. 2016;138(11):2602-2615.