August 16, 2022 | 8 minute read
Decades of Evidence-Based Cancer Science
Karen Collins, MS, RDN, CDN, FAND is AICR’s Nutrition Advisor. Karen is a speaker, writer and consultant who specializes in helping people make sense of nutrition news. You can follow her on Twitter @KarenCollinsRD and Facebook @KarenCollinsNutrition.
As AICR celebrates its 40th anniversary, one of its remarkable achievements is the development of solid, evidence-based Recommendations that help people prioritize steps they can take to reduce their risk of cancer. As strong as the evidence is behind the Recommendations, the logical question that follows is what this looks like when going from theory to practice .
Think of it like a baking recipe. When baking, you may think a combination of ingredients sounds right, but until you test the recipe, you don’t know. And better yet, a reputable recipe site or cookbook doesn’t just test a recipe once, but has multiple people test it to see if it consistently comes out as expected.
An important part of AICR’s mission throughout its 40 years has been to give people trustworthy information. It’s easy to be led off-track when you’re surrounded by false promises, and AICR has always aimed to serve as a counter-balance.
Testing the Lifestyle Recipe
Just as baking recipes need to be tested, research serves an important role in testing the “lifestyle recipe.” Do people who create lifestyles consistent with the AICR Recommendations really have lower risk of cancer than others?
Logic says yes, but good science needs more. We expect a lifestyle consistent with the AICR Recommendations to be associated with lower cancer risk, since they are all based on evidence rated strong according to specific criteria.
Other lifestyle choices also may be beneficial. But to provide reliable Recommendations, AICR’s Third Expert Report clarifies that evidence rated “limited suggestive” highlights an area for more research, not priorities for lifestyle changes.
One of the strengths of the AICR Recommendations is their help in setting priorities. Of all the healthy choices you could incorporate into your lifestyle, make sure you start with a focus on those highlighted in the 10 Recommendations instead of getting “lost in the weeds.”
Scores to Study AICR Recommendations in Real Life
Population studies that follow people over time are vital to answer questions about lifestyle’s association with chronic diseases like cancer that develop over many years. Scientists create scoring systems that use data they collect about eating habits and other lifestyle choices to assign points for how close the choices people make come close to the AICR Recommendations. Then they look at whether people’s scores are associated with cancer-related outcomes
In the earliest studies that examined whether cancer risk was associated with how people’s lifestyle fit with the AICR Recommendations, different scientists created slightly different scoring systems.
Then in 2018, following publication of AICR’s Third Expert Report and the latest update to the Cancer Prevention Recommendations, a new scoring system was unveiled. A collaborative group involving AICR/WCRF, the National Cancer Institute and a researcher involved in previous Recommendation-scored studies developed a standardized scoring system . This, along with the group’s guidance for its use, provides a stronger foundation for considering results of one study about lifestyle’s fit with the Recommendations in the context of findings from other studies.
Testing the Recipe: What Score-Based Studies Show
An analysis based on earlier studies that used similar, but somewhat differing, systems to score lifestyle fit with the Recommendations from the AICR/WCRF Second Expert Report included 20 studies exploring the association between a Recommendations-based score and cancer.
People with higher scores (indicating lifestyles more closely aligned with the Recommendations) were less likely to develop cancer than those with lower scores. Among specific cancers, risk of breast and colorectal cancers were most often studied.
Across studies, each one-point increase in score was associated with a lower risk of breast cancer (regardless of hormone receptor or menopausal status), colorectal cancer and lung cancer. No clear associations with score were found for risk of prostate cancer. However, one study found that among newly diagnosed cases of prostate cancer, higher scores were associated with lower odds of highly aggressive forms of prostate cancer.
Scores indicating lifestyle choices closer to the AICR/WCRF Recommendations were associated with fewer deaths from cancer and from all causes combined among people healthy at the start of a study, and with higher survival in people who had cancer.
Studies conducted since the development of the 2018 standardized scoring methods continue to tie higher scores (lifestyles closer to the AICR Recommendations) with lower overall cancer risk and lower risk of several of the most common cancers.
Cancer risk is lower among people with the highest scores compared to people with the lowest scores.
And it’s not all-or-nothing. Across a number of studies, analysis also shows that each 1-point score increase is associated with some reduction in risk. A 1-point increase could come from meeting one additional Recommendation, or from doing a little better on two Recommendations.
What about People Who Have Had Cancer?
Research is more limited about associations of lifestyles that fit the AICR Recommendations among people living with and beyond cancer. Several studies among people who have had colorectal cancer show higher Recommendations-related scores associated with better health-related quality of life. That includes better physical and cognitive function and less fatigue. Researchers following people for several years after diagnosis of non-metastatic colorectal cancer found that those with a lifestyle consistent with the 2018 AICR Cancer Prevention Recommendations had lower cancer-specific and overall mortality, especially when looking at the score without the component related to weight.
Looking at whether scores for how lifestyle meets the AICR Recommendations predict outcomes among cancer survivors will contribute valuable insights for designing survivorship programs that can be tested in randomized trials, and for providing advice to cancer survivors while we await the results of those trials.
But this research has even more complications than studies of lifestyle scores in people who have not had cancer.
Chicken or the egg? When higher lifestyle scores are related to less fatigue and better functioning in daily life after cancer, is it the healthier lifestyle that produces these outcomes? Or are people who function better more able to prepare healthy foods and include physical activity?
Weight: long-term or changing? Even for the cancer types with risk clearly increased by obesity, the point awarded for healthy weight in the lifestyle score can be complex in cancer survivors. Adiposity after a cancer diagnosis reflects pre-diagnosis weight and weight change after diagnosis. Even among people with obesity, unintentional weight loss that results from cancer or its treatment can be linked to worse outcomes. And that’s especially true if that includes loss of muscle.
When in the cancer journey? Lifestyle choices can change for everyone across time, but this is especially true for cancer survivors. For some types of cancer, side effects of cancer or its treatment can have short-term effects on diet and activity. Studies show that some people are highly motivated to create healthy lifestyle habits immediately after treatment. But with time, the challenge of long-term behavior change without adequate support can mean that a score based on earlier habits no longer applies. So when—or how often—should lifestyles fit with the Recommendations scored in these studies?
Recommendations-Based Lifestyle Scores: Lots of Progress, More Research Needed
The research we have using scores for how lifestyle fits the AICR Cancer Prevention Recommendations is still the tip of the iceberg compared to important questions that remain.
Answers to these questions will shape how people work at creating healthy lifestyles and influence the advice health professionals provide.
Does a 1-point increase in score have the same association with lower cancer risk regardless of how it’s achieved?
Does a fit with each Recommendation count equally? Or since certain cancers have more evidence related to some Recommendations than others, for specific cancers, should a match with some Recommendations be weighted more heavily than others?
Take-Home Messages for Today
We can’t expect to prevent all cancer cases from ever occurring. But from AICR’s earliest days through the present, research continues to show ever more clearly that many cancer cases don’t need to happen. And there’s good reason to expect that lifestyle choices can make a difference even after a cancer diagnosis.
Some valuable learnings for today:
Studies using scoring systems show that lifestyles don’t need to be perfect to help. Each step closer to meeting the AICR Recommendations seems to make a difference.
Based on these studies, we see that—unfortunately—many people are not living lifestyles consistent with the AICR Recommendations. The good news is that this means we have the potential to create meaningful reductions in the toll cancer is taking today.
Research using scoring systems provides the strongest evidence about reducing cancer risk. But, consistent with the advice in the AICR Third Expert Report, people living with and beyond cancer should talk with their personal health-care provider about how the AICR Recommendations fit them. Unless individual circumstances dictate otherwise, after cancer treatment has concluded, these Recommendations provide the best advice available today.
The progress you see today in research about lifestyles that meet the AICR Recommendations is an important aspect of the many dimensions of progress in accomplishing AICR’s mission over its 40 years:
Research is getting better and stronger in providing answers about diet, physical activity and weight/body composition related to cancer risk and survival.
Recommendations are based on careful analysis of best available research.
The American Institute for Cancer Research helps the public understand the relationship between lifestyle, nutrition and cancer risk. We work to prevent cancer through innovative research, community programs and impactful public health initiatives.