Increasing the amount of ultra-processed food in a person's diet proportionately increases their risk of cancer, a large study has found.
An examination of the food intake and health of nearly 105,000 people found that for every 10% more factory-processed food someone consumes, there is a 12% greater risk of them developing the disease.
Fizzy drinks, packaged breads and cakes, crisps, sweets, sausages, bacon and ham, instant noodles, and frozen or chilled ready meals were found to be associated with the increased risk.
The research by teams from the Sorbonne in Paris and the University of Sao Paulo also suggested there was an 11% increase in the risk of breast cancer.
The study looked at 104,980 healthy French adults with an average age of 43 and asked them about their eating habits.
After an average of five years, the adults were asked whether they had been diagnosed with cancer, and their answers were compared with their medical records.
While eating more ultra-processed food was associated with an increased risk of cancer, there was no significant link between less processed foods – such as canned vegetables, cheese and fresh bread – and cancer.
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Consuming fresh or minimally processed foods – such as fruits, vegetables, pulses, rice, pasta and fresh meat – was associated with a lower risk of cancer overall.
The study's authors say: "Several surveys … have suggested that ultra-processed food products contribute to between 25% and 50% of total daily energy intake.
"This dietary trend may be concerning and deserves investigation. Several characteristics of ultra-processed foods may be involved in causing disease.
"In this large prospective study, a 10% increase in the proportion of ultra-processed foods in the diet was associated with a significant increase of greater than 10% in risks of overall and breast cancer.
"Further studies are also needed to better understand the relative effect of nutritional composition, food additives, contact materials, and neoformed contaminants in this relation."
The authors say ultra-processed foods often have a higher content of total fat, saturated fat, and added sugar and salt, along with a lower fibre and vitamin density.