Fiolet T, Srour B, Sellem L, et al. Consumption of ultra-processed foods and cancer risk: results from NutriNet-Santé prospective cohort. BMJ. 2018;360:k322.
Population-based cohort study
To assess the prospective associations between consumption of ultra-processed food* and risk of cancer
Participants in this study comprise the French NutriNet-Santé cohort (2009-17), which includes 104,980 adults (median age 42.8 years).
Study Parameters Assessed
Dietary intakes were collected using repeated 24-hour dietary records, designed to register participants’ usual consumption for 3,300 different food items. Items were categorized according to their degree of processing using the NOVA classification, a food classification system based on the extent and purpose of industrial food processing. Cancer cases were identified and confirmed using self-reports, medical records, data from the French national health insurance system, and the French national mortality registry.
Associations between ultra-processed food intake and risk of overall, breast, prostate, and colorectal cancer assessed by multivariable Cox proportional hazard models adjusted for known risk factors.
Ultra-processed food intake was associated with higher risk of breast cancer (n=739 cases) and overall cancer (n=2,228 cases). For a 10% increment in the proportion of ultra-processed food in the diet, the hazard ratio [HR] was 1.12 (95% confidence interval [CI]: 1.06-1.18; P for trend<0.001) for overall cancer and 1.11 (CI: 1.02-1.22; P for trend=0.02) for breast cancer. That means a 10% increase in the proportion of ultra-processed foods in the diet was associated with a statistically significant 12% increase in the risk of overall cancer and 11% increase in risk of breast cancer. These results remained statistically significant after adjustment for several markers of the nutritional quality of the diet (lipid, sodium, and carbohydrate intakes and/or a Western pattern derived by principal component analysis).
The American Institute for Cancer Research claims that about a third of the most common cancers in the world could be avoided by changing lifestyle and dietary habits in developed countries.1 Within the naturopathic profession we have seen statements that suggest as many as 95% of cancers are preventable by diet and lifestyle.2 This seems exaggerated and leaves us wondering: Precisely how much risk for developing cancers can be attributed to diet?
In recent years the diets in many countries have shifted dramatically toward higher amounts of ultra-processed foods, which are foods that have undergone multiple physical and chemical processes to increase their palatability, shelf stability, safety, and affordability.3
Surveys conducted in Europe, the United States, Canada, New Zealand, and Brazil have suggested that these ultra-processed foods now contribute between 25% to 50% of total daily energy intake.4-7 While it may be hard for us to imagine this level of consumption, we have to remind ourselves that we naturopaths, and our patients, are not representative of the average global consumer.
If every 10% increase in calories derived from ultra-processed foods is associated with an 11% increase in overall cancer, we certainly have a serious problem brewing.
There are a number of reasons why ultra-processed foods might increase risk of cancer. They have a higher total fat and saturated fat content than less processed foods. Fat consumption may, or may not, be associated with risk for some types of cancer (prostate cancer, yes; breast cancer, no). The low vitamin density and high sugar and salt content of these foods may also play a role. The low fiber content affects gut biome and thus may change cancer risk.8 Processing may lead to formation of carcinogenic chemicals such as acrylamide, heterocyclic amines, and polycyclic hydrocarbons.9,10 Food packaging may contain carcinogens that leach into the food during storage or during preparation, such as bisphenol A. Some food additives, such as sodium nitrite, though legal to add to processed meat, may still be carcinogenic.
The very concept of studying the effects of food processing on disease risk is still in its infancy. It wasn’t until this NOVA classification system was created in the last year or 2 that these effects could be potentially quantified.11
While these data only seem to confirm a message we have been trying to teach our patients for decades, the degree of impact is surprising. If every 10% increase in calories derived from ultra-processed foods is associated with an 11% increase in overall cancer, we certainly have a serious problem brewing. Many segments of the population consume far more than 10% of their energy from ultra-processed foods.
Many of our patients believe that foods labeled as natural, organic, genetically modified organism (GMO)-free, or gluten-free are healthy choices. None of these labeled categories measure degree of processing and little data associates these categories with significant inverse cancer risk. Thus for patients who want to reduce their risk of cancer, reducing consumption of ultra-processed foods now appears to be a decent evidence-based choice in food selection.
*The paper under review defines ultra-processed foods according to the NOVA Classification system and includes the following:
“mass produced packaged breads and buns; sweet or savory packaged snacks; industrialized confectionery and desserts; sodas and sweetened drinks; meat balls, poultry and fish nuggets, and other reconstituted meat products transformed with addition of preservatives other than salt (for example, nitrites); instant noodles and soups; frozen or shelf stable ready meals; and other food products made mostly or entirely from sugar, oils and fats, and other substances not commonly used in culinary preparations such as hydrogenated oils, modified starches, and protein isolates. Industrial processes notably include hydrogenation, hydrolysis, extruding, moulding, reshaping, and pre-processing by frying. Flavoring agents, colors, emulsifiers, humectants, non-sugar sweeteners, and other cosmetic additives are often added to these products to imitate sensorial properties of unprocessed or minimally processed foods and their culinary preparations or to disguise undesirable qualities of the final product.”