Diet-heart hypothesis: a zombie or written in scientific stone?


By Marika Sboros

The diet-heart hypothesis is a curious creature. To some scientists and physicians, the hypothesis that saturated fat causes heart disease is a zombie. Despite all the stakes driven deeply into its heart, it just won’t die.

To others, it’s written in scientific stone. And when it wasn’t centre stage, the hypothesis hovered in the wings at a groundbreaking conference in Zurich, Switzerland in June.

This is the second of a two-part review of the event that was a unique collaboration between global reinsurer SwissRe and The BMJ.  The venue was auspicious, Swiss Re’s Centre for Global Dialogue in Rüschlikon that houses its research arm, the Swiss Re Institute.

Dr John Schoonbee. Picture: David Ausserhofer

On why the reinsurer was involved in nutrition research, Swiss Re’s chief medical officer Dr John Schoonbee elaborated in an article that The BMJ commissioned and published as part of the conference. Co-authors of scientific papers had to include at least one scientist or expert with vastly divergent views from the rest.

Questionable policy decisions

Schoonbee and Elefteriadis have posed and answered questions in their article on why the understanding of nutrition was often poor. They say that’s because of conflicting evidence and vested interest influence. And that this has led to “questionable downstream policy decisions”. These decisions have “massively influenced the outcome of world health and individual wellbeing”. And the financial health of life insurance portfolios and national health systems, they say.

The right policy decisions would have a measurably different impact on individual and societal health.

Click here to read: Teicholz: How low-fat diets can cause a heart attack


To that end, Swiss Re has developed a targeted life insurance model. The aim, Schoonbee said, is to assess the population effect of nutrition strategies on health. Specifically, strategies to reduce longer-term risk markers associated with type 2 diabetes, prediabetes, and metabolic syndrome.

If all those affected followed such a strategy, the model estimates an annual reduction in total death claims of 13%, Schoonbee and Elefteriadis say. That translates to substantial gains for life insurers paying billions in death claims annually.

They also say that it would reduce premature loss of life from preventable, reversible conditions.

The conference organisers clearly hoped to clear some confusion with the four-day event. The diet-heart hypothesis was a malingerer throughout.

The first two days covered Food for Thought, the Science and Politics of Nutrition. Click here for a full speaker list. The last two days covered Redefining Diabetes, Putting a “Chronic, Progressive” Disease into Remission. Click here for a full speaker list.

Miracle meeting?

Chief among these: health claims around saturated fats – in other words, the diet-heart hypothesis. And low-carbohydrate, high-fat (LCHF) diets and their polar opposite low-fat, high-carb diets that dietary guidelines enshrine.

Willett and others vigorously disputed the notion of any terminal hole in the diet-heart hypothesis.

Canadian cardiology professor Salim Yusuf said that the hypothesis was the result of “brainwashing” by a “questionable study” many years ago. Yusuf is chair in cardiovascular disease at McMaster University Medical School in Hamilton, Ontario.

Prof Salim Yusuf. Picture: David Auserhoffer

He was referring, of course, to Ancel Key’s Seven Countries Study that he launched in 1958 but only published two decades later. It has become “ingrained in our DNA”, Yusuf said.

It is also the bedrock on which experts built the dietary guidelines that the US launched onto an unsuspecting public in 1977. And the rest of the English-speaking world followed thereafter.

Emerging consensus?

Yusuf is also principal author of the PURE study. PURE is the largest study investigating links between carbs, fats, cardiovascular disease (CVD) and death. Among conclusions: the more fat you eat, including saturated fat, the lower your risk of dying from heart disease. And the higher your carb intake, the more your risk of premature death rises.

That led to emerging consensus of sorts at the Swiss Re event. Yusuf and Tufts University nutrition professor Dariush Mozaffarian were among those who agreed that there was no evidence to support current guideline caps on saturated fat.

Source: D Mozaffarian

That could have looked like the death knell for the diet-heart hypothesis. Instead, it highlighted another major conference theme: what evidence to trust – or not. And through them all ran the perennial divide of plant-based diets and animal foods.

Mozaffarian can look like he sits in the middle with his graphic on foods to prefer, eat moderately (in the middle) and avoid completely. (See right)

Among proponents of plant-based diets were Willett and Nita Ghandi Forouhi (Cambridge) in the UK who support the view that plant-based diets are healthier.

They also say that “much of the evidence (epidemiological) suggests that replacing saturated fat with polyunsaturated fats (including plant oils) reduces the risk of coronary heart disease”.

Jaundice view of epidemiology

On the other side were those promoting animal foods as healthier – and a jaundiced view of epidemiology. The US contingent included Prof Stephen Phinney,  Dr Sarah Hallberg and science writers and authors Nina Teicholz and Gary Taubes from the US. From the UK were cardiologist Dr Aseem Malhotra, public health researcher Dr Zoë Harcombe and others.

US science journalist Nina Teicholz and UK Prof Martin White. Picture: Dietdoctor

Both epidemiology and RCTs came in for a sound thrashing via video link from Stanford University Prof John Ioannidis. Ioannidis said that 95% of nutrition research is “in bias”.

Epidemiology’s “typical recipe” of nutrition research leads to failure. He identified “large measurement error”,  “cherry-picking among multiple hypotheses” and food industry influence as obstacles. Also “strong beliefs” – personal, religious and cultural –  and “white hat bias”. That’s the term for “bias leading to distortion of research-based information in the service of what may be perceived as ‘righteous ends’“.

‘Hijacking’ of the evidence

RCTs also have “tremendous bias”, Ioannidis said.

Prof Dariush Mozaffarian (left) and Dr Aseem Malhotra. Picture” David Auserhoffer

Malhotra later told the conference that commercial interests have “hijacked” the best available clinical evidence. He also said that root cause of obesity and type 2 diabetes – and heart disease in general – was “flawed science”.

BMJ editor Dr Fiona Godlee soldiered on, looking for consensus. There was one big reversal in conventional thinking, she said: the demonization of fat. However, she expressed surprise that there did not appear to be any significant “mea culpa” from the scientific community that it had got things so wrong.

Taubes disagreed that there was any reversal. The debate has just  “transformed” from saturated fat as bad to neutral, he said. But the issue was now: “neutral compared to what?”.

Saturated fat is supposed to be “neutral” compared to carbohydrates but not to polyunsaturated fats (PUFAs) and vegetable oils. This implies either that saturated fat is harmful or that PUFAs and vegetable oils are beneficial.

Therefore, the argument clearly hasn’t gone away”, he said.

Silence a better option?

Teicholz said that where strong evidence was lacking, it would be better for experts to “remain silent” than make misguided claims. She suggested a way forward:  the guidelines should contain a new low-carb advice option. That would avoid changes to other guidelines – and anyone having to admit to error.


In an email to me, Willett said that the classical diet-heart hypothesis was proven. And there are “layers of evidence” to support benefits of a largely plant-based diet (such as a traditional Mediterranean diet) versus a primarily animal-based diet, he said.

The evidence includes superior effects on blood lipids, long-term epidemiologic studies and RCTs. These show “significant benefit of replacing saturated fat with PUFA that includes both N-6 and N-3 fatty acids”.

“All the evidence is in this direction, none in the opposite direction,” he said.

For proof, he referred to his Nutritional Epidemiology textbook, now in its third edition.

“Replacing saturated fat with refined starch and sugar will not reduce risk of heart disease and could increase risk,” Willett said. Replacement, therefore, “is key”.

Meat and dairy fat not optimal?

At the core of much discussion was high dietary glycemic load as a “serious problem”, Willett said. “However, it doesn’t mean that eating a lot of red meat and dairy fat is an optimal solution. There is a huge body of data of many types showing that it is not.”

He said that Ioannidis had misrepresented how epidemiology was conducted and the results of studies, Willett said. “He makes his living by trashing other people’s work and has never done any serious research himself – the greatest COI (conflict of interest) of all.”

Prof David Diamond

US specialist Dr David Diamond watched the conference on live-streaming and shared his impressions with me via email.

Diamond is professor of psychology and molecular pharmacology and physiology at the University of South Florida. He also has a personal and professional interest in diet and cardiovascular disease. He lost weight and improved his triglycerides by cutting carbs and eating butter, eggs and red meat.

Diamond shares his knowledge in online lectures, hospital “grand rounds” and invited lectures at international medical conferences.

He delivered the keynote lecture on statins and heart disease at the World Congress on Diabetes & Obesity in Riga, Latvia in 2015. His lecture so impressed clinicians that they honoured him with their award for “outstanding contribution to science”.

Diamond has his share of detractors who support the diet-heart hypothesis. Here’s his rebuttal to a cardiologist who said his views on statins are “dangerous”.

Flaws in diet-heart hypothesis

Diamond described the diet-heart hypothesis as “flawed and antiquated”.

In one study, Diamond and 16 co-authors (all MDs and/or PhDs, including cardiologists) rigorously assessed the hypothesis that people over the age of 60 with high levels of LDL-C ( so-called “bad cholesterol”) would have a higher rate of death from heart disease and all-causes.

They found the opposite. Elderly individuals with the highest levels of LDL-C had an equivalent or, in most cases, a lower rate of death, than those with the lowest levels. That was another stake in the diet-heart hypothesis.

Prof Jennie Brand-Miller

Diamond was strongly critical of University of Sydney nutrition professor Jenni Brand-Miller’s presentation. Brand-Miller said that processed food had great value because it made women’s lives easier by “allowing them to go back to work”.

She further claimed that a pregnant woman could harm her growing foetus if she reduced her carbohydrate intake.

New Zealand-based dietitian and academic Dr Caryn Zinn found that claim extraordinary, as Diamond and others found it.

‘Piffle quotient’

Diamond called it “perhaps the (conference’s) worst scientific moment”. Brand-Miller was “perhaps paid well by the food industry”, he said – a sentiment that others at the conference echoed. She also said that the food industry shouldn’t be blamed for doing what it was told to do: produce low-fat, high-carb foods.

Diamond said that Brand-Miller’s opinions represented a “piffle quotient”. It reached its highest level when an MD in the audience stated that it was “well-known that the Atkins diet (with its reckless sanctioning of consumption of saturated fat) caused every form of disease known to Western civilization, including cancer, obesity and diabetes”.

Click here to read: PHC lays low-fat diets to rest


Diamond paid tribute to Hallberg for responding to “this twaddle” by stating the obvious. It is simply that “carefully conducted research has shown that the Atkins diet has not been linked to these diseases”.

The coup de grâce for Diamond was criticism from a panel of Hallberg’s recent Virta study showing an improvement of all primary biomarkers of health for diabetics and pre-diabetics with a very low-carb diet compared to usual care.

Hallberg showed that a personalised (vegetarian or omnivorous) low-carb diet could be of great value. Yet panelists “obsessed over the fact that subjects could choose their own treatment option, rather than the study being sterilized with a random design”, Diamond said.

He described Willett as “a force in the nutrition field by virtue of the fact that he’s a Harvard professor”. As well, he has published a vast amount of (largely epidemiological) research “to support his plant-based diet agenda”.

‘Weapons of mass cardiovascular destruction’

When it comes to saturated fat, Willett considers beef and butter to be “weapons of mass cardiovascular destruction”, Diamond said.

The conference gathering reminded him of his primary area of research: one of the most famous, intense neuroscience debates. These involved two great neuroanatomists of the 19th century who had opposing views of the brain’s structure.

 Spanish anatomist Ramon y Cajal provided strong evidence that brain cells were unique and separate elements. Despite the overwhelming evidence in favour of Cajal’s position, Italian anatomist Camillo Golgi believed that the brain was composed of a continuous network of neural fibres.

Click here to read: Saturated fat causes heart disease? Bollocks – Kendrick


When they shared a Nobel Prize for their research in 1906, the debate continued in their acceptance speeches. In it, each one said he was right and the other was wrong.

Decades later, after both had died, the invention of the electron microscope ended the debate, Diamond said. Photographs of individual neurons unequivocally demonstrated that each brain cell was a separate element physically isolated from other cells. Therefore, the evidence proved Cajal right, he says.

Golgi refused to accept overwhelming evidence that his reticular theory of the brain was wrong. Similarly, Willett’s assertion that a plant-based diet is healthier than a diet with animal fat is based on “a myopic approach that ignores or dismisses contrary findings”, Diamond said.

The ‘Golgi’ of nutrition?

Willett will “prove to be the Camillo Golgi of the nutrition field”, he said.

Nutrition science needs the equivalent of an electron microscope photograph to end the debate on issues of saturated fat and the value of the low-carbohydrate diet as a diabetes and obesity treatment.

“Ultimately, the equivalent of the decisive photograph in the nutrition field would be recognition that food that raises blood sugar, not consumption of meat, cheese, butter and eggs in large part cause the diseases of Western civilization,” Diamond said.

Many, if not most, divisions disappeared during the last two conference days. Hallberg, medical director at Virta Health, took centre stage to present her team’s research. It is the first clinically-proven treatment to show that type 2 diabetes really is reversible safely and sustainably without drugs or surgery.

There were no dissenting voices and rightly so as Hallberg let the evidence speak for itself.

She also dismissed the diet-heart hypothesis. The saturated fat debate is “over”, Hallberg said. “We are pretty much done with it and we now need to get that message across.”

As a result, low-carb is just one of three effective options to treat and reverse type 2 diabetes that include bariatric (stomach) surgery and caloric restriction.

In other words, there really is no diet that is one-size-fits-all and patient choice “is key”, she said.




    I find this very encouraging because I have always believed that the impasse that exists between the two sides can only be resolved by sitting down and talking to each other. When they really staring talking then maybe the name calling will also become a thing of the past. Nobody listens when they are being insulted

    The link above takes us beyond the positions of the two camps into a realm of nutritional study which makes far more sense than anything that I have heard from either camp

  2. When a doctor says something is “Well known” but can produce no evidence, he or she is repeating dogma learnt many years previously.

    The only thing keeping the diet-heart hypothesis alive is idealogy and the blinkered refusal to look at inconvenient evidence. There will come a time when we look back at the low-fat period as the nutritional dark ages. It will join ‘miasma’ and bloodletting in the dustbin of damaging medical advice.

  3. Since my wife passing a tear ago, I changed my diet completely from conventional HCLF to HFLC and have lost 10 Kgs, reduced my insulin use by 1/3 and am feeling physically better off. Meal sizes have also ahrunken as a result.

  4. Good summary, Marika. Thank you. The evidence for the benefits of the diet humans have been following for thousands of years (meat, vegetables and fruit, excluding grains) is constantly ignored. I can’t believe the stupidity of Brand-Miller’s comment “processed food had great value because it made women’s lives easier by ‘allowing them to go back to work’.” At what cost? Poor health caused by a poor diet? No wonder she was rubbished.

  5. It’s noticeable on Twitter that the Militant Vegans are the staunchest defenders of the diet-heart/lipid hypotheses and still regard Ancel Keys as a demigod.

    I’m with Peter Cleave, who pointed out that it was unthinkable that a modern disease could be caused by an ancestral diet.

    Then of course there’s the unassailable logic of dieticians “we know that low fat diets work, it’s just that nobody follows them”. The corollary of that is that we secretly ate low fat diets from when we evolved until they were invented a few decades ago, then we all suddenly stopped following them.

    Excellent conference in terms of science being presented, but The Authorities are now doubling down on stupid.

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