To lower cancer risks, study shows that food choices matter

It has long been believed—but with few large-scale epidemiological studies to prove it—that ultra-processed foods can contribute to a number of cancers. A new European observational study, based on results from the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort study, offers more proof validating the issue. The EPIC study goes one step further by showing how diet alternatives can result in a lower risk of certain cancers. The study appears in Lancet Planetary Health (doi:10.1016/S2542-5196(23)00021-9).

The EPIC cohort study included participants from 23 universities, university hospitals, and cancer research centers in 10 European countries recruited from March 18, 1991, to July 2, 2001. The researchers administered dietary questionnaires to determine each subject’s food and drink consumption. They identified participants with cancer by checking cancer registries and other sources, such as health insurance records and follow up questioning. Participants were excluded if they had a cancer diagnosis before recruitment, and other factors they believed might distort the research. Of the more than 521,000 EPIC subjects, 450,111 were included in this study, of which 318,686 were female (70.8%) and 131,425 were male (29.2%).

“We performed a substitution analysis to assess the effect of replacing 10% of processed foods and ultra-processed foods with 10% of minimally processed foods on cancer risk at 25 anatomical sites using Cox proportional–hazards models,” the researchers wrote.

“We do not consider our study ground-breaking, since other cohorts like Nutrinet Sante, UK Biobank, etc., have published similar results,” says study author Inge Huybrechts, PhD, a nutritional epidemiologist and head of the lifestyle exposure and interventions team at the World Health Organization in Lyon, France. “However, we would like to underline that it is the largest multi-center prospective cohort study conducted so far, with multiple cancer endpoints and careful control for multiple testing that confirm that our findings are robust. In addition, we [were] the first cohort to validate our food processing indicators against food processing biomarkers, which further supports our findings” [doi: 10.3389/fnut.2022.1035580].

The researchers found that a diet that focused on minimally processed and fresh foods, including whole grains, dairy products, nonstarchy vegetables, and even coffee, may reduce the risk for developing several cancers overall, while cancer risks increased when diets included more processed and ultra-processed foods.

The study also reported that when 10% of processed foods were replaced by minimally processed foods, the risk for cancer overall was reduced by 4%, and the risk for several specific cancer types was significantly reduced, including the risk for esophageal adenocarcinoma (43%) and hepatocellular carcinoma (23%).

Substituting minimally processed foods for ultra-processed foods also appeared to lower cancer risk, but not by as much, and there were fewer cancer sites for which the authors found significant associations in relation with ultra-processed foods than with processed foods. Specifically, substituting minimally processed foods for 10% of ultra-processed foods lowered the overall cancer risk by only 1%, the risk of esophageal squamous cell carcinoma by 20%, and the risk of hepatocellular carcinoma by 27%. “Most of these associations remained significant when models were additionally adjusted for BMI, alcohol and dietary intake, and quality,” they wrote.

The researchers theorize that ultra-processed and processed foods might increase cancer risk through obesogenic properties and low nutritional value. “Diets rich in ultra-processed foods tend to have a low dietary quality and a high energy density, and are associated with obesity, an established risk factor for at least 13 cancer sites, including the head and neck,” the researchers wrote.

Because the EPIC cohort is quite large and heterogeneous, the researchers believe their investigation linking food processing and cancer risk has greater reliability for uncovering differences in populations, and why this current study found more links for different cancers than what had been previously reported.

Caroline Um, PhD, MPH, RD, principal scientist in epidemiology research at the American Cancer Society (ACS) in Atlanta, Georgia, says that this study goes beyond previous studies because the authors also examined what may happen if highly processed foods are substituted with less-processed, unprocessed, and minimally processed foods, which are broadly linked with lower risks of certain cancers. “This is consistent with the current evidence that has been used to inform the ACS Diet and Physical Activity Guidelines for Cancer Prevention and the findings of the World Cancer Research Fund/American Institute for Cancer Research. They recommend consuming a wide variety of fresh fruits and vegetables and whole grains and limiting red and processed meats and sugary beverages.”

Dr Huybrechts says that the study results demonstrate that the industrialisation of the past decades and the continued trend toward greater industrial processing may be positively associated with the risk of overall cancer and several specific cancer types. “Furthermore,” she adds, “in this study we demonstrated that higher BMI [alone] cannot explain this positive relationship; other factors like food processing contaminants and additives may also play a role. These findings shed light on some potential mechanisms contributing to these associations, [which need] to be investigated further in future analyses.” She specifically anticipates using food additive and other food processing biomarkers in addition to industrial trans-fat.

Even though the study was conducted in Europe, Dr Um believes that the results would be similar for North American diets. “It’s possible that highly processed foods in Europe are similar to those found in the US. However, there are several general considerations about these foods.” She mentions that a major limitation of most studies examining highly processed food consumption is that foods may be misclassified because detailed information about each food item is not available. “Regardless of whether a study utilizes food frequency questionnaires or 24-hour dietary recalls, it is difficult to collect information about what individuals consume every day, so studies may still underestimate or miss the types of processed foods being consumed.

“However,” Dr Um adds, “we still do not understand the potential mechanisms by which highly processed foods affect cancer risk and development, so it is difficult to provide specific dietary guidelines about highly processed foods at this time.”

Dr Um says that another factor to examine is which foods are classified as “highly or ultra-processed.” She says that most studies utilize the NOVA classification system, but some of the foods classified as ultra-processed (NOVA 4) may not be foods that we tend to think of as being highly processed. “ACS recommends limiting the consumption of processed meats, which is an ‘ultra-processed food’ that has been consistently associated with higher risk of colorectal cancer.” She notes that other NOVA 4 foods include packaged snacks, candies, and cookies, and also baby formula, cold cereals, and low-fat fruit-flavored yogurt.

Under the NOVA system, highly processed foods can widely vary and can contain many non-nutritive ingredients, such as preservatives, emulsifiers, flavorings, artificial sweeteners, and other chemicals, says Dr Um. “We don’t know how each of these things may be related to cancer risk, so we need to better understand this first in order to understand how highly processed foods may impact health,” she says. “Dietary recommendations have not yet changed as a result of the new evidence on ultra- or highly processed foods, but it is possible that future dietary recommendations will consider the composition of foods and the potential health impact of individual ingredients.”

“We hope cancer researchers consider our findings and suggested mechanisms in future research and, if possible, examine these putative mechanisms further in well-designed clinical trials that can evaluate the impact of food processing on cancer-related biomarkers and health outcomes,” adds Dr Huybrechts.