Another day, another overblown food scare
The claim that eating processed meat will kill you is built on shoddy evidence and more than a dash of snobbery.
The top story in the UK media this morning is the claim that processed meat is killing us. This is the latest example of the British media churning out food scares like they were cheap sausages.
‘Processed meat blamed for one in 30 early deaths’, declares the Daily Telegraph. ‘Processed meat “is to blame for one in 30 deaths”: scientists say a rasher of cheap bacon a day is harmful’, says the Daily Mail in the true spirit of ‘churnalism’, while the addition of ‘cheap’ to the headline is surely designed to confirm the prejudices of its snobbier readers.
The BBC, which has made a veritable full English breakfast of this story this morning, summed it up as follows: ‘Sausages, ham, bacon and other processed meats appear to increase the risk of dying young, a study of half-a-million people across Europe suggests. It concluded diets high in processed meats were linked to cardiovascular disease, cancer and early deaths.’
However, the reality is that the methods used in such studies are so crude that drawing sweeping conclusions from this evidence is fraught with difficulties.
The findings are drawn from a long-running study of European eating habits, the European Prospective Investigation into Cancer and Nutrition (EPIC), which was ‘designed to investigate the relationships between diet, nutritional status, lifestyle and environmental factors and the incidence of cancer and other chronic diseases’. Subjects from 10 countries were recruited into the study between 1993 and 1999. They were given a questionnaire about their eating and lifestyle habits, while their weight, height, waist and other measurements were taken.
Here’s the ‘meat’ of the study, as described in the BBC report: ‘One in every 17 people followed in the study died. However, those eating more than 160g of processed meat a day – roughly two sausages and a slice of bacon – were 44 per cent more likely to die over a typical follow-up time of 12.7 years than those eating about 20g.’ (One important thing not mentioned in the media is that, after adjustment for measurement errors, no significant link was found between red meat and early death, only processed meat.)
So the risk of someone dying during the study was still pretty low. In absolute terms, that summary suggests that over 94 per cent of the people in the study survived. So, very roughly, maybe 92 per cent of the heaviest meat eaters survived and 96 per cent of the lowest meat eaters survived, with most people somewhere in between.
Professor Sabine Rohrmann, from the University of Zurich, told the BBC: ‘High meat consumption, especially processed meat, is associated with a less healthy lifestyle. But after adjusting for smoking, obesity and other confounders we think there is a risk of eating processed meat. Stopping smoking is more important than cutting meat, but I would recommend people reduce their meat intake.’
But you can only really adjust for the confounders you think of. As we’ve seen with these kind of processed meat studies in the past, the sort of people who eat a lot of processed meat tend to be very different from those who do not, in a whole host of different ways.
Indeed, the press release for the new study makes this point: ‘In general, a diet high in processed meat was linked to other unhealthy choices. Men and women who ate the most processed meat ate the fewest fruit and vegetables and were more likely to smoke. Men who ate a lot of meat also tended to have a high alcohol consumption. A person’s risk of premature death (increased risk of all-cause mortality) increased with the amount of processed meat eaten. This is also true after correcting for confounding variables, although residual confounding cannot be excluded. However, a small amount of red meat appeared to be beneficial, which the researchers suggest is because meat is an important source of nutrients and vitamins.’ [My emphasis.]
Indeed, confounding factors are built into the methods of the study itself. Studying nutrition is notoriously difficult. For example, let’s say that a subject says that for breakfast they ate the two sausages and one slice of bacon mentioned earlier. The researchers must then guess the weight of the meat involved. Were they large sausages or skinny chipolatas? What were they made of: were they pure meat or cheap bangers packed out with soya and rusk? Was the bacon thin and streaky, or broad back bacon? Was it smoked or unsmoked? How was it cured? Do we measure the raw weight or the cooked weight? Even over something as straightforward as this, there is plenty of room for uncertainty – and that all assumes that subjects can remember exactly what they ate when confronted with a questionnaire.
Moreover, these measurements can never tell us what a study subject actually ate over the years – they are no more than snapshot guesstimates of people’s actual diets. While the researchers attempted to control for this by using other methods to assess the diets of a sample of the subjects involved, error is inevitable.
The study concludes: ‘In this population, reduction of processed meat consumption to less than 20 g/day would prevent more than three per cent of all deaths. As processed meat consumption is a modifiable risk factor, health promotion activities should include specific advice on lowering processed meat consumption.’ Would you give up salami and chorizo and sausages because of that size of risk? Who, apart from some tofu-munching lunatics, would give up bacon – probably the tastiest thing humans have ever produced – to eke out a few extra months of life? Not me.
There is a lot of guesstimating going on here. Even after all this, the size of the effect is small. Previous claims about processed meat have focused on cancer, but here the increased risk of cancer was just 11 per cent. The bigger, all-cause mortality figure of 44 per cent was mostly due to cardiovascular disease, a risk which even the researchers suggest may be overstated.
Claiming that such a small effect can therefore be the basis of sound dietary advice is just nonsense – but it is nonsense that is repeated all too frequently. The result is to create unnecessary fear about perfectly good food and confirm the prejudices of those who think that processed food is only fit for the masses.