Once again the news media is highlighting the supposed dangers of consuming too much ham, bacon, sausages and other forms of processed meat. This is based on the results of a European study involving 448,568 men and women aged between 35 and 69 years old at the outset. The habitual diet was assessed over a period of 12 months. During the follow-up period there were 26,344 deaths (1). The report concluded:
“The results of our analyses suggest that men and women with a high consumption of
processed meat are at increased risk of early death, in particular due to cardiovascular
diseases but also to cancer. In this population, reduction of processed meat consumption to
less than 20 g/day would prevent more than 3% of all deaths. As processed meat
consumption is a modifiable risk factor, health promotion activities should include specific
advice on lowering processed meat consumption.”
Much of the official dietary recommendations is based on epidemiological studies which attempt to assess the food consumption patterns and then relate them to other factors such disease incidence and death rates. It must be emphasised that any associations which are obtained from this type of investigation do not demonstrate cause and effect. In order to identify specific causes much detailed research must be done. Ideally we need to understand precisely what is happening in the body to relate the cause and effect.
While epidemiological studies can help to identify causes of disease and death they certainly do not provide the proof which is needed if people generally are to be advised on what they should be eating. Unfortunately there are far too many examples of how this information is being misused with disastrous results. The Seven Countries Study by Ancel Keys is still used to justify the concern about fat, cholesterol and heart disease even though it has been totally discredited.
It is absolutely essential to appreciate that this latest report is just another epidemiological study and while it is possible that eventually there may prove to be some validity we are still a long way away from reaching that point.
The big problem is that the major causes of death which are the chronic diseases of the heart and arteries plus the various forms of cancer are multi-factorial. Hence it is extremely difficult to tease out the specific causes, the weight that relates to each of these and how they interact.
Considering the current study we find that those who consumed the most red meat and the most processed meat in general consumed fewer fruits and vegetables than those with low intake. They were also more likely to be current smokers and less likely to have a university degree. Men with high red meat consumption consumed more alcohol than men with a low consumption, which was not seen in women.
When it comes to smoking it was found that there was a statistically significant interaction between smoking and processed meat consumption, with mortality being significantly increased among former smokers and current smokers but there was no association among those who had never smoked. This means that those with the highest consumption of processed meat were also those at the greatest risk of dying because of their smoking habits.
The researchers have therefore subjected the raw data to various manipulations in order to attempt to allow for the effect of other factors which influence the disease and death rates. It really is in the lap of the gods whether this exercise can be done with any degree of accuracy because the quality of the data is questionable.
This is illustrated by the fact that the report claimed to have found a statistically significant interaction with body mass index, in which the association between processed meat consumption and all-cause mortality was stronger in lean than in overweight and obese participants. The fact that the association was stronger in those who were lean (presumably with a BMI of 20-25) is entirely expected since those in the “overweight “category (BMI 25-30) have a greater life expectancy than those with a normal BMI(See Blog 11). It would be very interesting to know what assumptions the research team made when doing this particular calculation!
It was also noted that those with a lower fruit and vegetable intake had a higher overall mortality in the highest consumption category of processed meat. So the question is
“How much of the increased death rate is due to the increased consumption of processed meat, how much is due to the low intake of fruit and vegetables and how much is due to ither factors which have not even been considered??”
David Colquhoun has considered in detail some of the earlier reports which focus on the relationship between meat consumption and death rates. He makes very relevant and interesting comments which are well worth reading(2). Here is a comment taken from his blog:
“Although the new study, unlike the earlier ones, shows signs for a relationship between the amount of red meat eaten and risk of death, the confounding factors (total calories eaten, weight, smoking etc) are so strong that the evidence for causality is critically dependent on the accuracy of the corrections for these factors, and even more dependent on their not being another factor that has not been included”
Despite the results of previous studies, especially those done in the USA, this European study did not confirm that a high consumption of red meat is associated with an increased death rate.
I will continue to enjoy my bacon and sausages although my preference is for those products which are high quality and hopefully free of horse meat!