Are our dietary slogans evidence-based?

Photo by Hansjörg Keller on Unsplash

Dietary advice is often communicated through slogans, such as: eat less saturated fat; eat more polyunsaturated ‘vegetable’ oils (even though they’re not made from vegetables); eat less salt; eat more fibre; eat more grains and cereals; eat less cholesterol; eat less ‘red’ or processed meat; drink more water; eat more fruit and vegetables and so on. An attraction of slogans such as these is that they come across as decisive, persuasive and memorable. It is taken for granted that they are science-based and that the evidence for them is definitive.

But, what if the science underlying them hasn’t even been done, or is more inconclusive than reported, or is poorly done science, or uses weak study designs, or applies only to a subset of the population, or is subject to biased analysis, or misrepresents the significance of the findings, or is not scientifically published if it doesn’t conform to prevailing opinion, or is overblown sensationally in the popular media?

Unfortunately for public health, none of those dietary slogans are founded on strong scientific evidence.

Saturated Fat

Take one example to highlight the lack of science: the saturated fat (sat-fat) slogan. This is probably the mother-of-all dietary slogans.

Surely, there must be substantial science to support the health benefits of eating less saturated fat for this slogan to have persisted for so long.

Well, no, not from definitive scientific studies. The best scientific evidence we have available indicates that dietary saturated fat does not increase the risk of heart disease or stroke. The biggest risk it poses is an increase in the enjoyment of food.

If nutrition science was a rigorous science, then the sat-fat hypothesis would have been rejected as false decades ago, and other risk factors for heart disease sought (such as sugar or insulin resistance). Instead, there have been shenanigans aplenty to prop up this hypothesis, including not publishing data that don’t support it. The first major randomised control trial (RCT) of the sat-fat hypothesis was carried out in Minnesota between 1968–73 in almost 10,000 participants, 20–97 years of age. A RCT is the gold-standard scientific method in this context. The trial tested whether replacing saturated fat with polyunsaturated corn oil would lower blood cholesterol and thereby reduce heart disease. They found that corn oil did lower blood cholesterol, however this increased mortality (all-cause death) — the lower that blood cholesterol was driven, the greater the mortality.

Rather than publishing these findings, the investigators (who expected their study to support the sat-fat hypothesis) bundled everything into archive boxes and stored it in the basement, where it remained for ~40 years. The data were rediscovered ~2011, recovered from magnetic tapes and punch cards, analysed using modern methods, and the full results finally published (2017). However, the sat-fat hypothesis has become unassailable, and the results of the study have had little impact. Science alone is not enough, and I will explain why later.

The 1960s-era Sydney Diet Heart Study was set up to answer the same question and ultimately suffered the same fate — it found that replacing dietary saturated fat with polyunsaturated oils increased the risk of death from coronary heart disease. The data were never published by the investigators, but were recovered and independently published in 2013.

Failure to publish undermines truth, but that only matters if the truth matters.

Advocates for the sat-fat hypothesis will always be able to find studies to support it. However, these studies are invariably observational (not RCTs), meaning they are statistical rather than scientific. They look for association and cannot show causation, they are confounded by numerous uncontrollable factors any of which could variably contribute to causation, and they produce ‘evidence’ so weak it should be dismissed in any case.

These considerations are endemic to mainstream nutritional science. Certainly, there are scientists doing good work in diet and health, but they rarely get on the radar. If they do, they soon get shot at. Mainstream nutritional science is ruthlessly protective of its hegemony.

Here’s an example from 2019. An international group of scientists revisited the evidence against dietary red meat. They noted that the evidence was from observational studies and therefore weak. Their analysis of all available studies led them to the conclusion that eating red meat was not harmful and that there is no reason to alter our eating patterns. They published 6 papers on various aspects of this topic in the Annals of Internal Medicine — a prestigious peer-reviewed medical journal. Mainstream nutritional science reacted with hostility to this conclusion and demanded the articles be retracted. In other words, that the papers be removed from the journal and quashed. Retraction is a serious step for a scientific journal to take, and usually only enacted when scientific fraud or serious flaws are uncovered. In this case, the journal rejected the demand — this one got under the nutritionist radar. Still, there will be instances where discordant studies can be sidelined by other means (e.g. restricting funding, manipulation of the peer-review system, editorial pressures, academic intimidation, etc.).

Nutritional Scientism

There is a problem with the term ‘Nutritional Science’ — just calling something science doesn’t make it so. Still, nutrition started out with good scientific intentions, building on the life sciences (biology, chemistry, physiology). The first success, from the 19th century, was in recognising the importance of macronutrients (protein, fat, and carbohydrate) for energy and health. Then, the beginning of the 20th century saw what was arguably nutrition’s greatest moment — the identification of nutrient-deficiency diseases and their causes. Vitamins were discovered, the importance of minerals recognised, and several serious medical conditions treated (scurvy, beriberi, rickets etc).

However, by the mid 20th century, nutrition started to lose its way by thinking that it could go beyond nutrient-deficiency to predict and manage life itself, in the form of determining what constituted the elements of diet and health. This advice was formulated over time, and influenced by various factors such as the rise of nutritional epidemiology (observational studies), the expansion of large-scale crop agriculture and food processing, the involvement of the State and an increasing interest in ‘health’. It took a while, but during this process, nutritional science morphed into a kind of nutritional scientism — the superficial and simplistic use of science in the service of nutritional ideology. Instead of an accumulating evidence-base, dietary advice was increasingly built around a sense of righteousness, the virtue of plants, the decadence of meat and the embrace of modernity.

The State became involved, issuing guidelines and establishing expert committees to direct population health. Meanwhile, Big Food, Big Ag, Big Pharma and Big Marketing converged on the messaging and flourished. These commercial entities do not prioritise our health, their responsibility is to their shareholders. Other entities take over when our health deteriorates.

And it has deteriorated. We are living through an unprecedented era of non-communicable diseases (NCDs) that were once rare (type 2 diabetes, Alzheimer’s disease, heart disease, cancer, non-alcoholic fatty liver disease…). For decades, nutritional scientism has run an uncontrolled, and unrepentant, experiment on our health that has failed us. The scale of the failure, and the horrendous consequences for individuals living with advanced NCDs, qualifies this experiment as a crime against humanity.

Nutritional Bullshit instead

I’ve used the term Nutritional Scientism up to now, but that’s rather dry and academic. Nutritional Bullshit is a term more to the point. Furthermore, I will now show that it is a theoretically appropriate term, not just colourful language.

The concept of bullshit has received academic attention — there’s a theory of bullshit. In 2005, a Princeton University Professor of Analytic Philosophy, Harry Gordon Frankfurt, published a short monograph with the title “On Bullshit”. It became a New York Times bestseller. His opening sentence reads:

One of the most salient features of our culture is that there is so much bullshit.”

Hear-hear. He goes on with the intention “to begin the development of a theoretical understanding of bullshit […] the most basic and preliminary questions about bullshit remain, after all, not only unanswered but unasked.”

His central thesis is that there is a fundamental difference between bullshit and lying. To lie, one must at least know the truth. “It is impossible for someone to lie unless he thinks he knows the truth. Producing bullshit requires no such conviction.” Bullshit may be true or false, it doesn’t matter — Frankfurt regarded the essence of bullshit to be an indifference to the truth. The bullshitter is interested in persuading the listener to their view instead.

Which explains why Nutritional Bullshit is an appropriate term. I don’t believe that most mainstream nutritionists are deliberately lying — more likely they are bullshitting. They have formulated rules (and built careers) on diet and health and it doesn’t matter if they are true or false, it matters that they persuade us to their way of thinking. It matters that they matter.

This perspective can also explain why newer and more rigorous scientific studies (debunking the sat-fat hypothesis, for example) don’t make a difference. It’s because the truth doesn’t matter — the bullshitter is indifferent to how things really are.

There is a futility in trying to convince people with science if they’ve already been persuaded by bullshit.

Further reading:

Minnesota Coronary Study:

Sydney Heart Study:

Detailed summary of the red meat papers:

Summary editorial of the red meat papers:

88% of American adults are metabolically unhealthy: University of Carolina study.

Nutritional Scientism (pay-walled):

Harry Frankfurt, book: “On Bullshit

Harry Frankfurt, YouTube




Science of cooking, eating and health. Retired neuroscientist.

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Science of cooking, eating and health. Retired neuroscientist.

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