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Bacon rashers, statistics, and controversy

BMJ 2019; 367 doi: https://doi.org/10.1136/bmj.l5989 (Published 14 October 2019) Cite this as: BMJ 2019;367:l5989

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Red meat restriction or banning: do dietary guidelines need higher evidence?

There is since the end of WWII, a battle in the field of human nutrition: animal products are vilified by some academic authors on the grounds of studies merely observational.

Those academic authors took power and influenced the nutritional guidelines. The consequences of official recommendations in terms of human health and political decisions stir up some disputed assertions. This opinion (https://blogs.bmj.com/bmj/2019/10/09/bacon-rashers-statistics-and-contro...) sums them up. T. Spector and C. Gardner discussed the recent recommendations issued by Canadian researchers (https://annals.org/aim/fullarticle/2752328/unprocessed-red-meat-processe...) that there is no evidence to cut on red meat because of health risks. It is not surprising that such a sceptical attitude is unbearable for those who believe that the weak and unconstant associations between meat consumption and chronic diseases and even death are non-questionable. However, in those studies, the type of meat was very imprecise, as the type of transformation, that those associations were mainly found in quartiles of high consumption and predominate in groups of people with a risky lifestyle (male sex, smoking, alcohol). More, despite or because the conventional food pyramids, where red meat consumption is strongly discouraged, the number one problem in public health is diabesity.

The authors began their piece with significant confusion.

Bacon is not red meat. In mixing them authors perfectly exemplified the risks of error in questionnaires of observational studies (OS). In mixing bacon, red meat, processed meats and environmental issues authors began to add incomprehensiveness to an already complex issue. They continued on this path, refuting RCT for nutrition studies. It is nonsense to make a rule for drugs and another for diets. The high profile authors, evoked in this opinion, made their career by making such a double standard an obvious knowledge and at the same time selling their observational studies with a low association between factors as fuzzy as the Mediterranean diet, grains, fat, dairy or meat... It is a shame that OS of 10 years or more were published with only one or two dietary assessments by self-reported questionnaires at the beginning. Aside from the fact that other academic authors disagree with this impossibility to do RCT on diets, several very high-quality papers were published and recently Kevin D. Hall did such an RCT which shows that junk food causes weight gain on a short time basis (https://www.ncbi.nlm.nih.gov/pubmed/31105044). Patients and physicians are worth high-quality studies and fortunately there are several means to get rid of OS.

The first is the RCT which brings quality information in order to help to solve the obesity epidemics that high profile nutritionists failed to curb. It is untrue to assert the contrary. By designing RCT it is possible to precisely assess each type of food or food group in the setting of a clear hypothesis. Randomization will balance the mistakes in questionnaires and control of diet will suppress the confusion and temporal variations.

The second is the use of genetic variants as instruments to test the causal associations (https://diabetes.diabetesjournals.org/content/early/2019/06/05/db19-0153).

The third is personalised nutrition which is the way to discriminate the effects of nutriments xenobiotics or carcinogens on different genomes and epigenomes (https://www.bmj.com/content/361/bmj.k2173).

Authors defend the weakest evidence, aka association of factors because they seem reluctant to embark on causality studies.

Eventually, the authors made two assertions which are not relevant to red meat.

Is it necessary to point out that nitrites and acrylamide are not present in red meat? Technically, processed meat means pork, beef or duck that has been salted and cured, with or without smoking. A fresh pound of red meat is not processed. A hard stick of cured salami is. The health risk of bacon, if any, is largely to do with two food additives: potassium nitrate (known as saltpetre) and sodium nitrite. On the other hand, major food sources of acrylamide are French fries and potato chips; but also crackers, bread, and cookies; breakfast cereals those last foods that high profile nutritionists advise eating if they are made of “whole flour”. Animal studies and other "mechanistic studies" are not relevant to the new strict analysis of the OS about red meat by Canadian authors. Indeed they are only warning studies for launching clinical trials. No more no less. And another time the great carnivores do not exhibit cancers or CVD after eating meat all their lives. Animal studies could be flawed as well: giving meat to a non-carnivore is as a poor mechanistic study than giving a high-fat diet to rabbits to explain atheroma. Last but not least they didn't mention the 2010 review which showed that eating charred, smoked, well done red meat is associated with a higher risk of colorectal cancer only in smokers (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769029/)!

Interestingly one of the studies reviewed in this paper (https://www.sciencedirect.com/science/article/pii/S0027510702001641?via%...) didn't find any association between well done or very well done meat (processed or not) and health issues below 5 steaks/week. It is near the advice of the Canadian authors who concluded that until 3 steaks per week there is no measurable risk. Indeed the issue of cancer and meat consumption is linked to potential carcinogens. Surprisingly T. Spector and C. Gardner didn't mention the proven carcinogens in high temperature cooked red or processed meat: heterocyclic amines and polycyclic aromatic hydrocarbons. These organic compounds which are also produced by high-temperature cooking of white meat, fish and vegetable protein although in less quantity are not present in fresh meat nor in low temperature cooked meat.

Red meat banning is a disruption from the human ancestral diet. We should think twice before throwing away red meat production together with fossil fuels because of environmental issues. There are smarter means to curb anthropogenic emissions without endangering human health.

Competing interests: No competing interests

16 October 2019
Guy-André Pelouze
Thoracic and cardiovascular surgeon
Institut de Recherche Clinique
Pau, France