The big health news of the week is the claim that eating a diet high in processed meat can increase the risk of premature death due to cancer and heart disease.
The current media scare stems from a large Europe-wide study looking at diet and mortality, involving just under half a million people who were followed for an average of 12.7 years.
One of the main findings was that people in the study who ate the most processed meat (160g or more per day) had a 44% increased risk of dying during follow-up compared to those who ate the least (20g or less).
The link to red meat was less conclusive.
The researchers estimated that if we all ate less than 20g of processed meat (which is around a single small piece of bacon) a day, then 3.3% of all deaths could be avoided – which is where the media reports came from that processed meat is responsible for 1 in 30 deaths.
However, an important limitation (rightly highlighted by the authors) is the possibility that other health and lifestyle factors could be contributing towards premature death risks.
Nevertheless, the study does highlight the importance of eating a healthy balanced diet, containing a high amount of fruit and vegetables.
The study was carried out by researchers from the Institute of Social and Preventive Medicine, University of Zurich, Switzerland, and a large number of other institutions across Europe.
Financial support was provided by a range of European organisations including, government, charity and academic institutions.
The media stories are generally representative of the findings of this research, with most including the common sense advice that eating an occasional bacon sarnie won’t kill you – just don’t do it every day.
The claims that processed meat is responsible for 1 in 30 deaths are based on the researchers’ estimate that 3.3% of the deaths in this study could have been prevented if all those who took part in the study ate less than 20g of processed meat a day.
Many past observational studies have suggested that high levels of red meat and processed meat consumption could be linked to a range of diseases, including cardiovascular diseases and various cancers, such as bowel cancer.
However, it can be difficult in such studies to exclude the possibility that the effect is not directly due to red and processed meats as such, but is due to the influence of other health and lifestyle factors. For example, people who eat a small amount of red and processed meat may also be eating higher amounts of fruit and vegetables, exercising more, be less likely to be overweight, smoke, or drink excess amounts of alcohol.
In the same vein, people who eat lots of processed meat may have other unhealthy habits such as drinking lots of alcohol and being heavy smokers.
This was a large cohort study using data collected as part of the European Prospective Investigation into Cancer and Nutrition (EPIC) study.
EPIC is an ongoing cohort study including more than 500,000 participants from 10 European countries.
The researchers took data from the EPIC study to look at the association between red meat, processed meat, and poultry meat consumption, and the risk of overall mortality and cause-specific mortality.
Men (aged 40 to 70) and women (aged 35 to 70) were recruited to EPIC between 1992 and 2000 (depending on the European study centre). After excluding those with self-reported cancer or heart disease, or those who did not report on smoking status at the time of enrolment, there were 448,568 people in the study.
Dietary assessment was performed slightly differently depending on the country:
For the purposes of analysis, they grouped food products as follows:
Various other sociodemographic, health and lifestyle questions were also assessed at recruitment, including age, education, height and weight, medical history, alcohol consumption, and smoking history (current, past or never, including questions on frequency and type of tobacco smoked).
Follow-up of outcomes was to 2005-09, depending on the country, with an average follow-up of 12.7 years. Information on deaths and cause of death was obtained through record linkage with cancer registries, Boards of Health, and death indices in seven countries, and through active follow-up of participants (for example, mail, telephone, and medical records) in three countries.
Information on vital status could be obtained for 98% of the cohort, which is impressive given the size of the study.
Hazard ratios were calculated to examine the association between different types and quantities of meat and processed meat consumption and risk of death.
They adjusted analyses for the following cofounders:
Compared to men and women who ate lower amounts of red and processed meat, those who ate the highest amounts tended to also eat fewer fruit and vegetables, be more likely to smoke, and less likely to have a university degree. Men who ate the highest amounts of red meat also drank more alcohol than those who ate lower amounts. This result was not seen in women.
During the average 12.7 year follow-up, there were 26,344 deaths (6% of the cohort), of these, 37% were due to cancer, 21% due to cardiovascular disease, 4% due to respiratory disease, 3% to digestive tract diseases, and the remainder due to various other causes.
Overall, there was a link between increasing processed meat consumption and risk of all-cause mortality. In the model adjusted for all confounders:
The link with red meat was not as strong as for processed meat:
There was no link between death risk and poultry consumption.
The researchers estimated that 3.3% of all deaths could be avoided if all people ate less than 20g per day of processed meat.
The researchers conclude that their analysis supports a ‘moderate association’ between increased processed meat consumption and increased mortality, in particular due to cardiovascular diseases, but also cancer.
This is a useful study examining whether there is an increased risk of dying from any cause, and from specific causes, with increased consumption of red meat and processed meat. The link to red meat was less conclusive, but there appeared to be a consistent link between increasing processed meat consumption and mortality risk.
The study has many strengths, including that it followed a large number of adults from across 10 European countries for an average 12.7 years, with almost complete follow-up.
The study used reliable methods to assess mortality outcomes. Food frequency questionnaires will unavoidably include some inaccuracy (for example, inaccurate recall or estimation of intake).
However, the researchers did attempt to validate the information through a series of 24-hour recalls.
The researchers have adjusted their analyses for age, study centre, weight and height, smoking and alcohol intake, overall energy intake, physical activity levels and educational level.
However, as the authors rightly conclude, the main limitation of the study is that it cannot completely exclude the possibility of residual confounding – that is, that the effects of these demographic, health and lifestyle factors, or others unmeasured, have not been fully accounted for.
These limitations apart, the study provides reasonably good evidence to support the importance of eating a healthy balanced diet, containing a high amount of fruit and vegetables. At the same time, it is important to moderate your consumption of foods high in salt, fat and sugar, which includes many processed foods.
The occasional bacon sandwich or full English breakfast probably won’t do significant damage to your health. But these should be occasional treats and not a staple of your diet.