Ultra-processed foods, such as pre-made cakes, fizzy drinks, or nuggets, may be associated with a higher risk of cancer, a new study concludes.

Unhealthy processed snacks. Image credits: National Cancer Institute.

Generally speaking, processed foods tend to be bad for you. They’re often sweeter, richer in calories, and lower in healthy nutrients than their counterparts. There’s no strict definition for ultra-processed foods, though they typically involve a large number of additives (such as preservatives, sweeteners, sensory enhancers, flavors and processing aids), but little or no whole foods. A new study has found another reason to avoid these processed foods: they might be linked to cancer.

French researchers at the Université Sorbonne Paris Cité analyzed the diets of around 105,000 people for an average of five years. Participants were split into four equal groups, depending on how much processed foods they had in their diet.

Researchers found a correlation between ultra-processed foods and cancer — the more processed foods people ate, the higher the cancer risk, for all groups. When the proportion of ultra-processed foods increased by 10%, the risk of overall cancer increased by 12%, with the risk of breast cancer alone increasing by 11%. This is particularly worrying since previous studies have found that people are eating more and more processed foods. Americans get 61% of their calories from highly processed foods. Within this study, 18% of the people’s diet was ultra-processed.

Researchers note that the findings need to be replicated in different populations, but they also raise a red flag — if we start eating more and more processed foods, the burden of cancer will likely increase accordingly.

“If confirmed in other populations and settings, these results suggest that the rapidly increasing consumption of ultra-processed foods may drive an increasing burden of cancer in the next decades.”

Overall cancer risk according to quarters of proportion of ultra-processed food in diet. Image credits: Fiolet et al / BMJ.

However, not everyone is convinced by this study. It’s not that anyone’s saying that processed foods are good for you, but there are still a few points of debate. For instance, it’s not exactly clear what an ultra-processed food really is. In this study, researchers defined them as “mass produced packaged breads and buns; sweet or savosamry packaged snacks; industrialised confectionery and desserts; sodas and sweetened drinks; meatballs, poultry and fish nuggets, and other reconstituted meat products.” They also included instant noodles and frozen ready meals in the list. But Tom Sanders, head of the diabetes and nutritional sciences division at King’s College London, says that including “mass-produced” in the definition of ultra-processed foods seems arbitrary and unnecessary.

While on average, mass-produced foods tend to be less healthy, there’s no underlying reason why this is always the case. Conversely, there’s no reason why a small production batch is necessarily healthier. Taking a simple example, let’s say you have two breads — one that was mass produced and sold in the millions, and another that is produced by a local, artisanal bakery. Chemically and nutritionally, they could be the same bread but by the study’s definition, one might be ultra processed and the other might not.

Furthermore, the more pressing issue is that of causality. Essentially, this study has found a correlation, but there’s nothing to suggest that the processed foods themselves are causing the cancer. Even if they are, we don’t really know if they’re causing it directly.

Processed foods are known to affect your body in a number of ways, and that can have cascading effects. For instance, they make you fatter, and being fatter makes you more likely to suffer from cancer. Is there a separate mechanism through which they’re linked to cancer, or is it just because of the extra pounds? That remains to be answered.

Prof Linda Bauld, Cancer Research UK’s prevention expert, said:

“It’s already known that eating a lot of these foods can lead to weight gain, and being overweight or obese can also increase your risk of cancer, so it’s hard to disentangle the effects of diet and weight.”

However, there’s still a clear takeaway. There’s another study in an already impressive pile that says you should be careful not to eat too much processed food.

Journal Reference: Thibault Fiolet et al. Consumption of ultra-processed foods and cancer risk: results from NutriNet-Santé prospective cohort. https://doi.org/10.1136/bmj.k322