Eating large amounts of ‘ultra-processed' foods may increase a person's risk of developing cancer, a new study suggests.

Highly processed, or ultra-processed, foods include ready meals, packaged baked goods and snacks, sugary cereals and fizzy drinks. They often contain high levels of fat, sugar and salt, but are lacking in vitamins and fibre.

Several surveys carried out in Europe, the US, Canada, New Zealand and Brazil have found that these foods account for 25-50% of total daily energy intake.

While some studies have linked ultra-processed foods to an increased risk of obesity, high blood pressure and high cholesterol levels, strong evidence linking them to cancer has been lacking. So researchers in France and Brazil decided to investigate this further.

They looked at the potential link between these foods and the overall risk of cancer, as well as the specific risk of breast, prostate and colorectal (bowel) cancer.

They monitored almost 105,000 healthy French adults with an average age of 43, over an average of five years. A number of well known risk factors for cancer were taken into account, such as age, family history of the disease and smoking.

The study found that a 10% increase in the proportion of ultra-processed foods in the diet was linked with a 12% increased risk of cancer overall and an 11% increased risk of breast cancer.

No significant link was found for colorectal or prostate cancer.

The researchers also found no significant link between the risk of cancer and less processed foods, such as cheese and canned vegetables.

Consumption of fresh or minimally processed foods, such, as fruit, vegetables, rice, pasta, eggs and milk, was linked with a lower risk of cancer overall and breast cancer.

The researchers acknowledged that this is an observational study so no firm conclusions can be drawn about cause and effect, however they pointed out that the study sample was large and the research did take into account potentially influential risk 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," they commented.

They said that more work is needed to better understand the effects of food processing, however they added that policies which target product reformulation, taxation and the marketing of these ultra-processed products, along with the promotion of fresh or minimally processed foods, may contribute to cancer prevention.

Details of these findings are published in the British Medical Journal.