Juan José López, member of the Management Committee of the Nutrition Area of the Spanish Society of Endocrinology and Nutrition (SEEN), is against the controversial conclusions of the guide on human consumption of red and processed meat published in October.
Hasta ahora se recomendaba limitar el consumo de carne roja o procesada a 70 gramos al día. / Pixabay
Last October, the Annals of Internal Medicine magazine published a new clinical guide on the consumption of red and processed meat. Its main novelty is the assertion that there is not enough strong evidence to decrease its use and, therefore, it could continue to consume such products with the current frequency.
Until now it was recommended to limit it to 1-2 servings per week or 70 grams per day due to its potential carcinogenic effect and its relationship with cardiovascular pathology. All this in accordance with the recommendations made by the World Health Organization (WHO) in 2015 and other international agencies.
This guide breaks with these indications, based on four independent systematic reviews of the effect of consumption of red meat, processed meat or dietary patterns rich in these meats on the development of oncological pathology, cardiovascular disease and mortality from all causes.
The problem arises when analysing these revisions. Although there is a relationship between the use of these foods and the event studied -which has guided the recommendations of the different scientific societies until now-, the current study group alludes, from a methodological point of view, to the fact that the observed effect is small.
This data is quite relative, given that we consider the reduction of 3 servings per week of this type of products. If we take into account that the average consumption of red meat or processed meat per week in most developed countries is above the consumption of 7 rations per week, the reduction that this group of studies maintains moves away from the recommendations of the different societies (1-2 rations per week).
Therefore, if we were to extrapolate this reduction to usual consumption, assuming the limitations that this entails, the amplitude of the effect would be much greater and both the rate of disease events and deaths per year would probably change.
When considering the effect of the reduction of red meat/processed should be assessed studies such as the randomized European PREDIMED trial, which evaluated the Mediterranean diet pattern, which associates a reduction in weekly intake of red meat to two servings, and demonstrated the reduction of severe cases of cardiovascular disease, breast cancer, diabetes and atrial fibrillation.
However, the type of design of this clinical guide precluded the introduction of this and similar studies. On the other hand, another of the limitations observed by the authors is their quality, as they are mainly observational studies subject to a multitude of biases.
This factor is common in studies related to diet in the field of human nutrition and is very difficult to control. However, the methodology used to categorize this evidence was the GRADE method, which 'penalizes' observational studies.
Finally, the authors base part of the recommendation on a systematic review of studies in which health preferences and value were evaluated with respect to the change of the patients' usual diet.
This review concludes that omnivorous individuals are reluctant to change their diet despite the health damage they may cause. This argument is used by the authors to consider that it is more appropriate to maintain usual dietary patterns.
Perhaps the most convenient attitude is to consider new public health strategies when convincing people of the inadequacy of certain ways of eating rather than remaining immobile.
The development of this guide does not foresee the scenario that would be the most appropriate if we want prevention strategies that permeate public opinion. In other words, we must consider them as a way of bringing together existing knowledge, but assuming it is a body of evidence that requires more research.
Even so, almost all studies point in the direction that excessive consumption of red and processed meat can have a harmful effect on health. For this reason, our recommendations should be aimed at reducing this type of food as indicated in most clinical guidelines.
One of the limitations spotted by the authors is the difficulty in differentiating data collection between unprocessed red meat and processed meat, and in some cases the cooking methods and their carcinogenic potential are taken into account.
Therefore, the development of studies in which these factors can be differentiated would allow us to categorize the effect by adjusting for potential confounding factors.
Conducting clinical trials in which the direct effect of these foods is proven is complicated by the possibility of deliberately harming one of the groups.
A quality development of such trials should be oriented to the evaluation of eating patterns, in which each of the diets is well categorized.
This clinical practice guide and its recommendations have limited usefulness: its interpretation is subject to partially subjective appraisals (methodological limitations).
In summary, we cannot advocate maintaining eating patterns with important indications that they may harm the individual and, as health professionals, we must be cautious in how we translate the message obtained from the scientific evidence to society.