There may exist an association between intake of highly processed food in the diet and cancer. Published yesterday by The BMJ, the study suggests that while further exploration is needed, the rapidly increasing consumption of ultra-processed foods “may drive an increasing burden of cancer in the next decades.”
What are Ultra-processed foods?
Ultra-processed foods include packaged baked goods and snacks, sugary cereals, fizzy drinks, ready meals and reconstituted meat products. These foods tend to contain high levels of sugar, fat, and salt, and are lacking in vitamins and fibre. They are thought to account for up to 50% of total daily energy intake in several developed countries.
Although a few studies have linked ultra-processed foods to higher risks of obesity, high blood pressure and cholesterol levels, firm evidence linking intake to risk of disease is still scarce.
This study sought to evaluate potential associations between ultra-processed food intake and risk of overall cancer, as well as that of breast, prostate, and bowel (colorectal) cancers.
Their findings are based on 104,980 healthy French adults (22% men; 78% women) with an average age of 43 years who completed at least two 24-hour online dietary questionnaires, designed to measure usual intake of 3,300 different food items (NutriNet-Santé cohort study).
Foods were grouped according to degree of processing. Cases of cancer were identified from participants’ declarations validated by medical records and national databases over an average of five years.
A number of well known risk factors for cancer, such as age, sex, educational level, family history of cancer, smoking status and physical activity levels, were also considered.
The results show that a 10% increase in the proportion of ultra-processed foods in the diet was associated with increases of 12% in the risk of overall cancer and 11% in the risk of breast cancer. No significant association was found for prostate and colorectal cancers.
Further testing found no significant association between less processed foods (such as canned vegetables, cheeses and freshly made unpackaged bread) and risk of cancer, while consumption of fresh or minimally processed foods (fruits, vegetables, pulses, rice, pasta, eggs, meat, fish and milk) was associated with lower risks of overall cancer and breast cancer.
This study is an observational one, so no firm conclusions can be drawn about cause and effect. Moreover, a number of limitations are evident. For example, researchers cannot rule out some misclassification of foods or guarantee detection of every new cancer case. In saying that, the study sample was large and they were able to adjust for a range of potentially influential factors.
“To our knowledge, this study is the first to investigate and highlight an increase in the risk of overall – and specifically breast – cancer associated with ultra-processed food intake,” write the authors.
Further work is necessary in order to better understand the effects of the various stages of processing. However, the authors suggest policies targeting product reformulation, taxation, and marketing restrictions on ultra-processed products and promotion of fresh or minimally processed foods may contribute to primary cancer prevention.
In an associated editorial, Martin Lajous and Adriana Monge based at the National Institute of Public Health in Mexico, say this study provides
“an initial insight into a possible link between ultra processed foods and cancer” but “we are a long way from understanding the full implications of food processing for health and wellbeing.”
There are a number of challenges in understanding the aforementioned implications, such as identifying the precise elements in ultra-processed foods that could lead to cancer, and the potential impact of other unmeasured factors on the results.
The editorial concludes:
“Care should be taken to transmit the strengths and limitations of this latest analysis to the general public and to increase the public’s understanding of the complexity associated with nutritional research in free living populations.”