You may have seen the headlines of the: “Processed food, sugary cereals and sliced bread may contribute to cancer risk” ilk, as this recently published study (February 2018) was extensively covered in the media — the Times of London had a front page spread no less.
So I feel obliged to follow suit — albeit with a heavy heart: it’s one of those depressing exercises in which you’re sure you know the answer before you start.
It’s a mainly French study (well, it is about food) led by Thibault Fiolet, Mathilde Touvier and colleagues from the Sorbonne in Paris. It’s what’s called a prospective cohort study, meaning that a group of individuals, who in this case differed in what they ate, were followed over time to see if diet affected their risk of getting cancers and in particular whether it had any impact on breast, prostate or colorectal cancer. They started acquiring participants about 20 years ago and their report in the British Medical Journal summarized how nearly 105 thousand French adults got on consuming 3,300 (!) different food items between them, based on each person keeping 24 hour dietary records designed to record their usual consumption.
Foods were grouped according to degree of processing. The stuff under the spotlight is ‘ultra-processed’ — meaning that it has been chemically tinkered with to get rid of bugs, give it a long shelf-life, make it convenient to use, look good and taste palatable.
What makes a food ‘ultra-processed’ is worked out by something called the NOVA classification. I’ve included their categories at the end.
Relative contribution of each food group to ultra-processed food consumption in diet (from Fiolet et al. 2018).
And the result?
The first thing to be said is that this study is a massive labour of love. You need the huge number of over 100,000 cases even to begin to squeeze out statistically significant effects — so the team has put in a terrific amount of work.
After all the squeezing there emerged a marginal increase in risk of getting cancer in the ultra-processed food eaters and a similar slight increase specifically for breast cancer (the hazard ratios were 1.12 and 1.11 respectively). There was no significant link to prostate and colorectal cancers.
Which may mean something. But it’s hard to get excited, not merely because the effects described are small but more so because such studies are desperately fraught and the upshot familiar.
One problem is that they rely on individuals keeping accurate records. Another problem here is that the classification of ‘ultra-processed’ is somewhat arbitrary — and it’s also very broad — leaving one asking what the underlying cause might be: ‘is it sugar, fat or what?’ Furthermore, although the authors tried manfully to allow for factors like smoking and obesity, it’s impossible to do this with complete certainty. The authors themselves noted that, for example, they couldn’t allow for the effects of oral contraception.
The authors are quite right to point out that it is important to disentangle the facets of food processing that bear on our long-term health and that further studies are needed.
I would only add ‘rather you than me.’
Perforce in these pages we have gone on about diets good and bad so there is no need to regurgitate. Suffice to say that my advice on what to eat is the same as that of any other sane person and summarized in Dennis’s Pet Menace — and it’s not been remotely affected by this new research which, in effect, says ‘junk food is probably bad for you in the long run.’ But let’s leave the last word to Tom Sanders of King’s College London: “What people eat is an expression of their life-style in general, and may not be causatively linked to the risk of cancer.”
Fiolet, T. et al. (2018). Consumption of ultra-processed foods and cancer risk: results from NutriNet-Santé prospective cohort. BMJ 2018;360:k322 http://dx.doi.org/10.1136/bmj.k322
The ultra-processed food group is defined by opposition to the other NOVA groups: “unprocessed or minimally processed foods” (fresh, dried, ground, chilled, frozen, pasteurised, or fermented staple foods such as fruits, vegetables, pulses, rice, pasta, eggs, meat, fish, or milk), “processed culinary ingredients” (salt, vegetable oils, butter, sugar, and other substances extracted from foods and used in kitchens to transform unprocessed or minimally processed foods into culinary preparations), and “processed foods” (canned vegetables with added salt, sugar coated dried fruits, meat products preserved only by salting, cheeses, freshly made unpackaged breads, and other products manufactured with the addition of salt, sugar, or other substances of the “processed culinary ingredients” group).