Can eating junk food really cause cancer? Why we need to be super cautious about such claims

A new study from French researchers suggests a connection between highly processed foods and cancer, but critics claim the conclusions may not be as clear as they seem.

Can eating junk food really cause cancer? Why we need to be super cautious about such claims

Researchers at Universite Sorbonne Paris Cite investigated the diets of around 105,000 people for an average of five years. They found that if 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%.

The results hint at a link between eating ultra-processed food and the risk of cancer, with the researchers concluding: “the rapidly increasing consumption of ultra-processed foods may drive an increasing burden of cancer in the next decades.”

But a number of experts have called for caution before jumping to conclusions, citing questions around the definition of “ultra-processed” and the fact that poor diets tend to come alongside other cancer risks – such as smoking and a lack of exercise. Indeed, those that ate a lot of ultra-processed food were more likely to smoke, consume more calories in total, and take oral contraceptive. The researchers tweaked their analysis to reflect this, but admit that the impact of “unmeasured behavioural factors […] cannot be entirely excluded”.  

“This study suggests that eating more processed foods like fizzy drinks, crisps and biscuits could increase your overall risk of cancer,” said professor Linda Bauld, Cancer Research UK’s prevention expert, in a statement to Alphr.

“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.”

Bault noted that people “shouldn’t worry about eating a bit of processed food here and there based on this study”, adding that there is “good evidence” that too little fruit and vegetables and too much processed and red meat can contribute to some types of cancer.

Defining “ultra-processed”

In their study, published in the British Medical Journal, the researchers say that ultra-processed food includes “mass produced packaged breads and buns; sweet or savoury packaged snacks; industrialised confectionery and desserts; sodas and sweetened drinks; meatballs, poultry and fish nuggets, and other reconstituted meat products.” They also mention instant noodles and frozen ready meals.

Talking to the BBC, professor Tom Sanders, head of the diabetes and nutritional sciences division at King’s College London, said the definition of ultra-processes was problematic. He pointed to the notion that the study views mass-produced breads as ultra-processed and not artisan bread from a local bakery:

“This classification seems arbitrary and based on the premise that food produced industrially has a different nutritional and chemical composition from that produced in the home or by artisans. This is not the case.”

Sense about Science, a campaigning charity challenging the misrepresentation of science, took a similar approach in a tweet that draws attention to the number of chemicals in apples compared to Loveheart sweets:

The researchers of the paper themselves acknowledge that their results “should be confirmed by other large scale, population based observational studies in different populations and settings”. They also highlight that their study mainly involved middle-aged women with high-conscious behaviours, and that this “might limit the generalisability of the findings”.

The results may deliver an early insight into the health impact of processed food, but they are far from conclusive about a definite link between “ultra-processed” foods and cancer.

“Eating a balanced diet, avoiding junk food and maintaining a healthy weight are things we can all do to help stack the odds in our favour,” noted Bauld.

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