Poor Diet Linked To 80,000 Cancer Cases In The United States

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As many as 80,000 new cases of cancer reported in 2015 may have been diet related, according to results from a new study.

Colorectal cancer had the highest proportion of diet-related cases, with 38.3% of all cases associated with suboptimal diets. This was followed by cancer of the mouth, pharynx, and larynx, with almost 26% of cases linked to diet.

The highest cancer burden was associated with an insufficient consumption of whole grains and excess intake of processed meats. Middle-aged men and racial/ethnic minorities experienced the largest proportion of diet-associated cancer burden.

Dietary-linked cancers are comparable to those associated with alcohol intake, which are estimated to be 4% to 6% of all cancers, note the authors. Also, excessive body weight is associated with 7% to 8% percent of the cancer burden, and physical inactivity with 2% to 3%.

"Our study findings lend further support to the growing evidence by estimating the cancer burden associated with suboptimal diet at the national level," said lead author Fang Fang Zhang, MD, PhD, associate professor at the Friedman School of Nutrition Science and Policy at Tufts University, Boston, Massachusetts. "It underscores the opportunity to reduce cancer burden and disparities in the US by improving food intake."

She noted that these results reinforce the importance of addressing unhealthy diet at the population-level and evaluating the cost effectiveness of broad nutrition policies on reducing cancer burden and disparities in the US.

"These may include system-level changes in healthcare such as nutrition counseling and healthy food incentives being incorporated into healthcare, as well as nationwide food price policies, food labeling policies, nationwide educational campaign on healthy eating, and setting up nutrition standards for government food procurement, school meals, and restaurant meals," Zhang told Medscape Medical News.

The study was published online May 22 in JNCI Cancer Spectrum.

For the past two decades, the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) have issued have issued cancer prevention guidelines for weight management, diet, and physical activity. In addition, an ever-increasing number of studies have confirmed the link between various cancer types and lifestyle.

Focus on Diet Only

In this study, Zhang and colleagues separately estimated the cancer burden that could be directly attributed to poor diet, and also estimated the diet-associated cancer burden associated with age, sex, and race/ethnicity.

"Different from previous studies that have identified the associations between dietary intake patterns and cancer risk, our study quantified the number and proportion of new cancer cases that are attributable to poor diet at the national level," she explained.

To estimate dietary intake, they used a nationally representative sample of US adults who participated in the two most recent cycles (2013–2014 and 2015–2016) of the National Health and Nutrition Examination Survey, and selected dietary factors having "convincing "or "probable" evidence on cancer risk: fruits, vegetables, whole grains, processed meats, red meats, and total dairy products from research conducted by the WCRF/AICR. Risk estimates of diet and cancer relationships were based on meta-analyses of prospective cohort studies with limited evidence of bias from confounding,

An estimated 80,110 new cancer cases reported in 2015 were associated with the suboptimal intake of seven dietary factors, including low intake of vegetables, fruits, and whole grains and high intake of processed meats, red meats, total dairy products, and sugar sweetened beverages (SSB). This accounted for 5.2% of all invasive cancers that were reported for that year in adults ages 20 years or older.

The largest number of cancer cases that were associated with poor diet was colorectal (n = 52,225), followed by cancers of the mouth, pharynx, and larynx (n = 14,421), corpus uteri (endometrial cancer) (n = 3165), breast (postmenopausal n = 3059), kidney (n = 2017), stomach (n = 1564), liver (n = 1000), pancreas (n = 538), and adenocarcinoma of the esophagus (n = 475).

A suboptimal intake of whole grains was associated with the largest number and proportion of new cancer cases, followed by low intake of dairy products, a high processed meat intake, low vegetable and fruit intake, high red meat intake, and high intake of sugar-sweetened beverages.

Of the total number of cancer cases attributed to diet, 67,488 were attributed to direct associations with suboptimal diet, and 12,589 to obesity-mediated pathways.

Overall, the three leading dietary factors that attributed to cancer through direct associations were insufficient whole grain intake, insufficient dairy intake, and excess processed meat intake. Low fruit intake and high sugar-sweetened beverage consumption were the two main factors that attributed to body mass index-mediated pathways.

Differences in Subgroups

The authors also looked at the interaction of diet and age, gender, and race/ethnicity. As they expected, the highest number of cases was among older adults (age ≥ 65 years), but the proportion was higher in middle age groups (45-54 and 55-64 years) as compared with younger or older individuals.

Both the number of diet-associated cancer cases and proportion were higher in men compared with women. As compared with non-Hispanic whites, racial/ethnic minorities (non-Hispanic blacks, Hispanics, and others) had a higher cancer burden.

A number of factors may account for the higher rates among these subgroups. "It may reflect a high rate of suboptimal diet, a high rate of cancer incidence, or both," said Zhang. "For example, men overall have a higher cancer incidence rate than women, and men also consume a lower amount of fruits and vegetables and a higher amount of red [meat] and processed meat than women."

In addition, the researchers found that middle-aged Americans had worse dietary intake than older adults; this subgroup also had higher cancer incidence than younger adults. "Suboptimal diet accounted for a higher proportion of cancer burden attributable to diet among non-Hispanic blacks, Hispanics, and others than non-Hispanic whites. [This is] is largely due to suboptimal diet in racial/ethnic minorities," she added.

But across all subgroups, the top five dietary factors associated with cancer burden in the US were whole grains, dairy products, processed meats, vegetables, and fruits.

Translate Evidence Into Action

Nigel Brockton, PhD, vice president of research at the American Institute for Cancer Research, pointed out that while other studies have looked at modifiable factors as a group, this study only focused on diet. The results were primarily driven by colorectal cancer. "We know more about what causes and prevents colorectal [cancer] more than any of the other cancer types," he told Medscape Medical News. "According to their estimates, more than 50,000 cases of colorectal cancer are caused by poor diet."

The AICR recently came out with a list of 10 recommendations for cancer prevention. Brockton explained that when the list was published, the items deliberately weren’t numbered because it was a "package" of recommendations.

"The first one is to maintain a healthy body weight, the second is to be physically active, and then these are followed by dietary recommendations such as eating whole grains and vegetables," he said. "But this [study] is only about diet, even though we know that preventing cancer includes several lifestyle components.

"Their focus was on diet alone while our focus — even though it is aligned with this — is more lifestyle-based," said Brockton. "So many of these things are co-related, such as the type of diet of people who are overweight or obese, or who are physically inactive. That makes it difficult just to dissect out the 'diet part,' but if you do want to endorse a healthier approach, then you have to isolate it in order to change it."

Also commenting on the study for Medscape Medical News, Mingyang Song, PhD, assistant professor of clinical epidemiology and nutrition at the Harvard T.H. Chan School of Public Health, in Boston, noted that it is "not surprising that colorectal cancer had the highest proportion of diet-related cases, because colorectal cancer has the most evidence for its relationship with dietary factors."

"While the estimate of 38.3% is higher than I would expect," he said, "it may be due to the fact that rather stringent criteria have been used to define the optimal intake, such as the 125 g/day intake for whole grains."

These findings do lend further support to the growing evidence that diet is a key component in cancer risk and prevention, and Song emphasized that the critical next step is to translate the evidence into action. "Primary care definitely plays an important role, but changes at the policy and regulatory levels are also critical," he said.

This work was supported by awards from the National Institute on Minority Health and Health Disparities and the National Heart, Lung, and Blood Institute. Additional support was provided by the United Kingdom Medical Research Council Epidemiology Unit Core Support and an American Heart Association postdoctoral fellowship.

Senior author Dariush Mozaffarian reports honoraria or consulting from AstraZeneca, Acasti Pharma, GOED, Haas Avocado Board, Nutrition Impact, Pollock Communications, Boston Heart Diagnostics, and Bunge; scientific advisory board, Omada Health and Elysium Health; chapter royalties from UpToDate, and research funding from the National Institutes of Health and the Gates Foundation. Zhang and the other study authors have disclosed no relevant financial relationships. Broxton and Song have disclosed no relevant financial relationships.

JNCI Cancer Spectrum. Published online May 22, 2019. Abstract

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