How Many Cancers Can be Prevented by Improving Diet?

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A recently published study suggests that over 80,000 cancer cases are caused by poor diet alone (independent of obesity, inactivity and other contributing risk factors) in the United States every year.
Dr. Fang Fang Zhang, a cancer and nutrition researcher at the Friedman School of Nutrition Science and Policy at Tufts University, set out to estimate the cancer burden associated with poor diet. Dr. Zhang, and her team relied heavily on the best available estimates of cancer risk associated with each aspects of diet; these estimates were provided by the Third Expert Report published by the World Cancer Research Fund International (WCRF) and the American Institute for Cancer Research (AICR).

In our Q&A session, Dr. Zhang expands on the findings of her study and the need to reduce cancer burden and disparities in the United States by improving food intake.

  • You have chosen 7 dietary factors: whole grains, dairy products, processed meat, red meat, vegetables, fruits, and sugar-sweetened beverages – how and why were these specific factors selected?

To estimate the cancer burden associated with suboptimal diet, we utilized the risk estimates of diet and cancer relations based on meta-analyses of prospective cohort studies with strong evidence base. Most of the risk estimates came from the World Cancer Research Fund International (WCRF) and the American Institute for Cancer Research (AICR) Third Expert Report.

  • You emphasize in your study that it is important to examine the impact of these dietary factors in subgroups defined by age, sex and race/ethnicity. Why work with subgroups?

Certain population subgroups experience a greater cancer burden attributable to poor diet than others. Because diet is among the few modifiable risk factors for cancer, identifying disparities in preventable cancer burden associated with diet can inform policy priority areas to reduce cancer disparities through improved diet.

  • You also emphasize that it is important to assess the impact of diet independently of the impact of obesity. Why is the independent effect so important?

Obesity has been recognized as an important risk factor for 13 types of cancers. However, the cancer burden attributable to diet-associated obesity has not been quantified. Our study findings suggest that among the estimated 80110 new cancer cases attributable to poor diet in 2015, approximately 16% were due to obesity-mediated associations. For example, high consumption of sugar sweetened beverages (SSBs) increases the obesity risk and obesity increases the risk of 13 cancers. We estimated that more than 3000 new cancer cases in 2015 were attributable to high SSB consumption. Certainly, new cancer cases that are attributable to the direct carcinogenic effects of certain foods still account for the majority (84%) of the diet-associated cancer burden in the US. These include low consumption of whole grains, fruits, vegetables, dairy products, and high consumptions of red and processed meats.

  • How well do your estimates of the burden of cancer due to diet agree with previous estimates? Were there any surprises?

We estimated that the diet-related factors may account for 80,110 of the new invasive cancer cases reported in 2015, or 5.2 percent of that year’s total among U.S. adults. This percent was lower that some early estimates in the US and UK, ranging from 7% to 10% but was comparable to the estimate from a recent study in the US, which attributed approximately 5% of the cancer burden in the US to poor diet.

The percent of the cancer burden attributable to poor diet is similar to the percent of cancer burden associated with alcohol, which is 4 to 6 percent. Excessive body weight, meanwhile, is associated with 7 to 8 percent of the cancer burden, and physical inactivity is associated with 2 to 3 percent.

  • What do you see as the biggest opportunity coming out of this research? Does it suggest “low hanging fruit” (excuse the pun) for interventions or does it illustrate the size of the challenge with regard to changing dietary behavior?

Our study findings suggest that a substantial amount of the cancer burden in the US is attributable to low whole grain consumption and high processed meat consumption. These highlight the priority areas for dietary inventions to focus on for reducing cancer burden in the US. For examples, there have been no changes in the consumptions of processed meat in the past 15 years among US adults, despite the convincing evidence linking processed meat consumption and risk of some cancers. Although Americans have improved consumption of whole grains in the past 15 years, the average consumption of whole grains is still only one third of the recommended intake. Nutrition policies need to be proposed, evaluated, and implemented to increase whole grain consumption and reduce processed meat consumption for reducing the large amount of the diet-associated cancer burden among US adults. Obesity also contributes a large amount of cancer burden in the US. Nutrition policies to reduce obesity can also be cost-effective to reduce obesity-associated cancer burden. Cancer may take decades to develop. It might therefore be strategic to intervene with the children for reducing cancer burden, such as targeting sugar-sweetened beverage consumption among youth.

  • How important is the work conducted by AICR/WCRF in facilitating these types of analyses?

To estimate the cancer burden associated with suboptimal diet, we utilized the risk estimates of diet and cancer relations based on meta-analyses of prospective cohort studies with strong evidence base. Most of the risk estimates came from the World Cancer Research Fund International (WCRF) and the American Institute for Cancer Research (AICR) Third Expert Report. The work conducted by AICR/WCRF provides key data input that is critical for researchers like us to estimate the preventable cancer burden attributable to poor diet in the US and around the world.

  • We are bombarded with dietary advice on a daily basis, some of which is contradictory, and as an individual, it can be easy to feel you either cannot keep up or it is impossible to meet the standards suggested. Is it all down to personal choice and will power or should there be legislation by Congress to make it easier to make good choices and improve access to healthy options?

While we can promote optimal diet in motivated individuals, individual-based approaches are often costly and not sustained. Conversely, population-based strategies to improve diet such as food price polices (taxation and food subsidies), food labeling policies, setting quality standards, or mass media and education campaign, could have a broader, more powerful and sustainable impact. The limited public health budget also requires prioritizing the most cost-effective interventions for implementation. Thus, we think it is important to propose, evaluate, and implement population-based strategies such as nutrition policies to reduce cancer burden and disparities in the US.

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