It seems that every week we hear something new gives us cancer; Coffee, chocolate, bacon just to name a few recent outcries. But one food group that keeps being hounded as a villain is processed foods. The high-sugar, high-salt, low-nutritional-content foods. The foods we all know as unhealthy, but keep going back to. Why? Because they’re quick and simple, but most of all, they’re tasty!
The reason why there are so many conflicting pieces of research out there is because they look at correlations, not causation. There may be a correlation between eating a lot of X food and a higher rate of Y disease. This gives us an indication about what is good and what is not, but doesn’t prove it. The reduction in pirates correlates with an increase in global temperatures, but that doesn’t mean those swashbuckling sea dogs combated climate change! And there’s a good reason for that; how ethical would it be to purposefully expose individuals to diets which are linked with cancer? Not very. So we have to make do with associative studies.
However, the studies are getting better, more in depth and rigorous, taking into account lots of different factors. For example, a recent publication in the British Medical Journal (a high quality, peer-reviewed journal) used a highly studied cohort to identify strong links between certain foods and an increased incidence of cancer. They found that a 10% increase in ultra-processed foods such as biscuits, fast food and ice cream were associated with an increase in the rate of cancer by 12%.
The key difference about this study is the level of detail which test subjects have been studied, one example being keeping rigorous diet diaries over many years.
One big thing to keep in mind when reading any scientific study is what they actually say, not just what they appear to say. Is it causative or associative? Does it show the direct link between cause and effect, or is it just coincidence that the two things occur together? While in everyday life we often take these to be equivalent (because they often are), science is an evidence-based pursuit and links have to be proved.
High quality academic papers will make the level of certainty of a study clear, but how many people actually read primary scientific literature? I’d guess not many. And this is no dig at the general public- subscriptions to journals cost quite a bit and the language they use means that much of the literature is not accessible to the general reader. The most common place to hear scientific news is through the mainstream media (and more recently, social media). However, in using language which is more understandable, subtleties and qualifying criteria of the research are often lost. Mainstream media’s primary incentive is to make money and hard hitting (and even false) stories get read more!
While association between two factors is not evidence, and doesn’t necessarily mean causation, the fact that two things occur together is often a good indication that the two may be linked. For example, those who eat highly processed foods are more likely to get cancer. This has been shown to be true. However, is it the processed foods which cause the cancer? Those who eat processed foods are also more likely to have a poor diet in general, exercise less and have poorer socio-economic backgrounds. Each of these things are linked with cancer- do they all contribute or do only some? Or perhaps there is yet another factor which has not been seen that may cause the increase in cancer risk?
This recent study, while still associative, gives yet another strong indication that highly processed foods are partly to blame for an increased risk of cancer. Not only is the high fat, salt and sugar content thought to contribute, but also neo-formed contaminants (particles which are created under the heat treatment process of certain processed foods such as acrylamide) and potentially carcinogenic food additives.
Of course nobody is saying never to eat ice cream again or never touch another packet of sweets, but to be aware of the risks of eating them too much. Food is meant to be enjoyed. What is the point of living if you don’t enjoy treats every so often? But ultra-processed foods should be just that, a treat. Because after all, what’s the point of living 100 years of oat-meal misery instead of 80 years of occasional frivolity?