Nutrition and health: confusion is served

Cristina Roure

Red and processed meat, so reviled for years in all healthy eating guides, is back to happy days. Recently, the United States Department of Agriculture abolished the initiative promoted by Michelle Obama that proposed the inclusion of fresh fruits and vegetables in school cafeterias. The reason was to defend the freedom of the individual and the educational centres to offer a more nutritious meal following the preferences of the American population.

A great controversy has also surrounded the recent publication of a series of articles and an editorial in the Annals of Internal Medicine, which states that the evidence linking the consumption of red and processed meat with cardiovascular diseases, diabetes and cancer is too weak to recommend that adults limit their intake (1). The researchers explain their findings and the reason for their recommendations in the following video:

The publication has been heavily criticized by the True Health Initiative (THI), a non-profit organization whose mission is to promote healthy lifestyles. THI criticizes what it considers to be a tortuous analysis of the evidence and unjustified conclusions, and also accuses one of the authors of not having declared certain sponsorship conflicts that have been subsequently rectified by the magazine.

I am sorry to disappoint readers if they expected this article to shed light on resolving the red and processed meat controversy, and I already announce that here we will only limit ourselves to reflecting on the causes of this heated debate and some others like it.

It’s logical and desirable that major public health problems such as obesity, cardiovascular disease or cancer and their relationship to different lifestyles are very present in the headlines of the media and the debates on social networks. What is not so positive is the unbalanced importance given to certain isolated scientific studies in which the certainties are non-existent, but which lead to exaggerated messages and dogmatic and unjustified recommendations. Among these studies, we count those related to the effects of countless diets and certain nutrients or supplements on health, which are tremendously popular.

It’s the soap opera that deals with the effects of meat consumption on health or the comings and goings on cholesterol and about the weekly consumption of eggs, as well as other implausible findings on the benefits or risks associated with certain nutrients such as coffee, hazelnuts or tangerines (2). All this highlights the existence of conflicts of interest of all kinds, the magnitude of the limitations and cumulative biases of the research, as well as a certain ideological militancy that occurs in the field of food like no other.

The economic conflict of interest

The food and nutrition market is huge, even more so than that of Big Pharma and it’s not surprising that some interest groups try to promote more or less biased research and thereby influence consumption habits by promoting the amplification of their messages through social networks and the media. They are always ready to throw hyperbolic headlines about something as every day as food, which interests everyone and is part of their daily routine. The powerful food industry has a very important relative weight in the financing of nutrition research that generates these messages.

The sponsorship conflict is not the only one, since many nutrition experts are also authors of books that are authentic best sellers and, although their theses are not always supported by the evidence, they are sold as if they were absolute truths.

The "white hat" bias

There is also talk of the existence of a certain "white hat bias" in the research (remember that in Hollywood Westerns the "good" cowboy always wore a white hat). Thus, some habits are a priori "demonized" (those in the dark hat) and others "sanctified" (those in white), which distorts the research in favour of those that, also a priori, are considered more acceptable behaviours. What we eat is a central element of our culture and our identity. It’s also strongly connected to our most irrational selves, determining strongly ingrained preferences, beliefs and prejudices even among expert professionals. There are strong pressure groups that defend different diets for ideological, ethical or belief reasons - not related of course to scientific evidence - some diets over others (vegetarian, vegan, flexitarian, paleodiet, superfoods, etc.). It’s understandable to think that you cannot be healthy on such a sick planet, but automatically assuming that the healthiest diet for the planet is also healthy for humans is not based, despite some people, on scientific evidence.

Limitations and biases of nutrition research

Research in the fields of food, nutrition and, in general, that carried out on various lifestyles, raises a series of intrinsic methodological and approach difficulties. Non-randomized observational designs are often used, often retrospective, less reliable a priori than prospective randomized, double-blind clinical trials used in other interventions and which are not very feasible in this setting. Some claim to abandon these observational studies and promote prospective clinical trials, the gold standard in research (2).

However, others, such as David Katz of the True Health Initiative, claim that classical evidence assessment tools are not adequate for assessing the long-term effects of different lifestyle choices (3). Diet is not a controlled intervention as it would be, for example, a precise pharmacological intervention in a clinical trial limited in time. It’s difficult to measure and record it accurately and keep it unchanged throughout the test. And it’s also very difficult to attribute the health effects to any of the nutrients that make it up. According to Katz, the prevailing idea that the results of randomized clinical trials are consistently superior to observational cohort studies may not be valid for evaluating the very long-term cumulative effects of various lifestyles and nutrition in particular. If you are interested in learning more about the multiple biases in nutritional research, check out the following video by John Ioannidis:

In any case, as you can see, the confusion regarding nutrition is served. The composition of the diet and its effects on health is one of the most confusing and controversial areas of science out there.

Having a debate on whether to eat red meat or eggs more than two days a week, three or never, or whether a cup of coffee more or less can affect survival offers attractive headlines and feeds the social networks, always so eager to controversy and radical positioning. This bombardment of studies with discordant conclusions and contradictory messages does not generate more than perplexity and scepticism among citizens and professionals and, what is worse, distracts our attention from certainties such as the importance of eating a balanced diet as a whole, not smoking, not drink excessively and stay physically, cognitively and emotionally active to age better.

As John Ioannidis says, “A single scientific study, no matter how sophisticated and methodologically well planned it may be, never impacts the immediate directions to improve people's day-to-day health”. As professionals, we should keep that in mind.

Bibliography

1- Zeraatkar D, Han MA, Guyatt GH et al. Red and Processed Meat Consumption and Risk for All-Cause Mortality and Cardiometabolic Outcomes: A Systematic Review and Meta-analysis of Cohort Studies. Ann Intern Med 2019; 171:703–710.  

2- Ioannidis J. The Challenge of Reforming Nutritional Epidemiologic Research. JAMA 2018; 320: 969-970. 

3- Katz, DL, Karlsen, MC, Chung, M et al. Hierarchies of evidence applied to lifestyle Medicine (HEALM): introduction of a strength-of-evidence approach based on a methodological systematic review. BMC Med Res Methodol 19, 178 (2019).