Can eating foods that are “ultra processed” cause cancer

The headlines and articles distorted the findings of the study by suggesting that the foods studied are actually increasing cancer. The Guardian ran a more accurate headline. It said:

Cancer may be linked to ultra-processed food…

This accurately reflects that the study found a link between certain types of processed foods and an increased risk of cancer.

The study found that for every 10% increase in ultra-processed foods, there was a 12% rise in the risk of developing certain types of cancer. It is important to interpret this research with caution.

What was the methodology of the research?

The data comes from groupings of people. You can tell if something is associated with another, but you cannot prove that something caused it.

Read more: Clearing up the confusion between correlation and causation.

The analysis included 104,980 French adults – mostly women (78%) with a median age of 42.8 years – who were followed up from 2009 to 2017. They were asked to report what they’d eaten in the previous 24 hours on three occasions every six months for two years. The participants reported their usual intakes of more than 3,300 food items contained in a food and nutrient database.

Cancer cases were reported by self-reporting through health questionnaires. A doctor would then contact the patient to get details about the cancer. The medical records were reviewed by a committee of experts and linked with the databases of the French National Death Registry and the National Health Insurance System.

What foods were studied?

Food products were classified based on their “processing” using NOVA classification. This helped identify ultra-processed foods and drinks. The items are not modified but rather highly processed products made with components from food plus added nutrients and other additives using industrial processes.

The first group is made up of “unprocessed” or “minimally processed” foods, while the fourth group is made up of “ultra-processed food”.

The first group included all unprocessed plant parts, such as fruits, seeds, leaves, stems and roots, as well as fungi and algae. It also included animal products such as offal and muscle meats, as well as eggs and milk.

Unprocessed food, like eggs, was included in Group One. From shutterstock.com

In the first group, minimally processed food is that which has been processed in order to remove undesirable or inedible components, preserve it for storage or aging, or make it safe or edible. The minimal processes include roasting, grinding, drying, pasteurization, and boiling.

Foods in group four are those that contain a large proportion of components or additives derived from food or additives and little or no intact food from group 1. Soft drinks, packaged sweets and savory snacks, frozen meals, and reconstituted products were all included in group four.

Researchers calculated how much of a person’s total food intake came from ultra-processed products. Results were shown as Hazard Ratios, meaning that researchers compared cancer incidence in people who consumed more ultra-processed food to those with lower intakes.

Read more: It’s all relative: how to understand cancer risk.

Then what?

The researchers then evaluated the relationship between the consumption of ultra-processed food and the incidence of cancers in general, including breast, prostate, and bowel cancer.

These analyses were adjusted to take into account factors like age, gender, height, BMI (body-mass index), smoking, family history, education, and physical activity (so that they didn’t count those who are more likely to develop cancer for other reasons). In the analyses of breast cancer, adjustments were also made to account for factors such as the number and type of births, menopause status, hormonal contraceptive use, or oral contraceptive usage. All of these factors are known to increase the risk of breast cancer.

Read more: What causes breast cancer in women? What we know, don’t know and suspect

The statistics were further adjusted for fat, salt, and carbohydrate intakes, alignment with a Western dietary pattern, or both of these together. This was to make sure effects weren’t caused by these nutritional aspects rather than the processed aspect. They also excluded cases of cancer diagnosed during the first two years of follow-up because it’s possible this was already present from other causes.

About 19% of all food consumption, or about one-fifth, was ultra-processed. The results show that consuming 10% extra ultra-processed food by weight is linked to a 12% higher risk of developing cancer.

Highly processed foods are low in nutritional value. Shutterstock.com

Postmenopausal females had an 11% increased risk of breast cancer due to consuming ultra-processed food. Researchers found that this increased risk of cancer in general was present across all populations studied. These associations remained after adjusting for the nutritional quality of normal dietary intake or alignment with Western diet patterns.