Sugar versus fat: why so many scientists got it so wrong for so long

Looking for more background when I was writing previous post, I came across a very lengthy, but nevertheless interesting story in The Guardian. This long read is titled The sugar conspiracy and the subject is the battle between the theory that sugar is the (main) reason for the obesity epidemic and the established theory that fat was the culprit.

This is not something recent, the controversy originated already in the middle of last century and, although the fats theory was found to be ultimately wrong, the sugar theory was ridiculed, discredited and careers were ruined. It took fifty years for the theory to resurface, leaving the question why the top nutrition scientists got is so wrong for so long.

We hear that objection often in climate change discussions: so many scientists can’t be wrong for so long. Well, it is possible and the sugar theory is only one of its manifestations.

The most interesting part of the Guardian story is the tension between the scientist who first proposed this theory (John Yudkin) and his scientific adversary (Ancel Keys). It reads like the current controversy on climate change. Replace Yudkin with your favorite skeptic, Keys with your favorite alarmist, fats with CO₂, meat/dairy/sugar industry with Big Oil/Tobacco and the story sounds really modern. There are a lot of similarities between how the scientists in the two sciences treat those who are skeptical towards the consensus position.

This is the part that struck me the most (my emphasis):

Ancel Keys was intensely aware that Yudkin’s sugar hypothesis posed an alternative to his own. If Yudkin published a paper, Keys would excoriate it, and him. He called Yudkin’s theory “a mountain of nonsense“, and accused him of issuing “propaganda” for the meat and dairy industries. “Yudkin and his commercial backers are not deterred by the facts,” he said. “They continue to sing the same discredited tune.” Yudkin never responded in kind. He was a mild-mannered man, unskilled in the art of political combat.

That made him vulnerable to attack, and not just from Keys. The British Sugar Bureau dismissed Yudkin’s claims about sugar as “emotional assertions”; the World Sugar Research Organisation called his book “science fiction”. In his prose, Yudkin is fastidiously precise and undemonstrative, as he was in person. Only occasionally does he hint at how it must have felt to have his life’s work besmirched, as when he asks the reader, “Can you wonder that one sometimes becomes quite despondent about whether it is worthwhile trying to do scientific research in matters of health?”

Throughout the 1960s, Keys accumulated institutional power. He secured places for himself and his allies on the boards of the most influential bodies in American healthcare, including the American Heart Association and the National Institutes of Health. From these strongholds, they directed funds to like-minded researchers, and issued authoritative advice to the nation. “People should know the facts,” Keys told Time magazine. “Then if they want to eat themselves to death, let them.”

This apparent certainty was unwarranted: even some supporters of the fat hypothesis admitted that the evidence for it was still inconclusive. But Keys held a trump card. From 1958 to 1964, he and his fellow researchers gathered data on the diets, lifestyles and health of 12,770 middle-aged men, in Italy, Greece, Yugoslavia, Finland, Netherlands, Japan and the United States. The Seven Countries Study was finally published as a 211-page monograph in 1970. It showed a correlation between intake of saturated fats and deaths from heart disease, just as Keys had predicted. The scientific debate swung decisively behind the fat hypothesis.

Keys was the original big data guy (a contemporary remarked: “Every time you question this man Keys, he says, ‘I’ve got 5,000 cases. How many do you have?’). Despite its monumental stature, however, the Seven Countries Study, which was the basis for a cascade of subsequent papers by its original authors, was a rickety construction. There was no objective basis for the countries chosen by Keys, and it is hard to avoid the conclusion that he picked only those he suspected would support his hypothesis. After all, it is quite something to choose seven nations in Europe and leave out France and what was then West Germany, but then, Keys already knew that the French and Germans had relatively low rates of heart disease, despite living on a diet rich in saturated fats.

The study’s biggest limitation was inherent to its method. Epidemiological research involves the collection of data on people’s behaviour and health, and a search for patterns. Originally developed to study infection, Keys and his successors adapted it to the study of chronic diseases, which, unlike most infections, take decades to develop, and are entangled with hundreds of dietary and lifestyle factors, effectively impossible to separate.

To reliably identify causes, as opposed to correlations, a higher standard of evidence is required: the controlled trial. In its simplest form: recruit a group of subjects, and assign half of them a diet for, say, 15 years. At the end of the trial, assess the health of those in the intervention group, versus the control group. This method is also problematic: it is virtually impossible to closely supervise the diets of large groups of people. But a properly conducted trial is the only way to conclude with any confidence that X is responsible for Y.

Although Keys had shown a correlation between heart disease and saturated fat, he had not excluded the possibility that heart disease was being caused by something else. Years later, the Seven Countries study’s lead Italian researcher, Alessandro Menotti, went back to the data, and found that the food that correlated most closely with deaths from heart disease was not saturated fat, but sugar.

By then it was too late. The Seven Countries study had become canonical, and the fat hypothesis was enshrined in official advice. The congressional committee responsible for the original Dietary Guidelines was chaired by Senator George McGovern. It took most of its evidence from America’s nutritional elite: men from a handful of prestigious universities, most of whom knew or worked with each other, all of whom agreed that fat was the problem – an assumption that McGovern and his fellow senators never seriously questioned. Only occasionally were they asked to reconsider. In 1973, John Yudkin was called from London to testify before the committee, and presented his alternative theory of heart disease.

A bemused McGovern asked Yudkin if he was really suggesting that a high fat intake was not a problem, and that cholesterol presented no danger.

“I believe both those things,” replied Yudkin.

“That is exactly the opposite of what my doctor told me,” said McGovern.

Remember, Keys was wrong all along, while Yudkin was right.

Later in the article there was also this (my emphasis):

This makes scientific inquiry prone to the eternal rules of human social life: deference to the charismatic, herding towards majority opinion, punishment for deviance, and intense discomfort with admitting to error. Of course, such tendencies are precisely what the scientific method was invented to correct for, and over the long run, it does a good job of it. In the long run, however, we’re all dead, quite possibly sooner than we would be if we hadn’t been following a diet based on poor advice.

Scientists are social beings after all and prone to biases. What I find striking in the article is the recognizable way the consensus science was portrayed and how the competing theory was dismissed/ridiculized. There was the unwarranted certainty in which the saturated fats theory was brought, its institutionalization, the official advice, the uncritical attitude towards the consensus position, the one-sidedness, the reluctance to debate, the role of the media and so on. It is interesting to see how a consensus can survive for such a long time, even if it is based on obvious flawed research, even with peer review that should prevented this issue.

I also like the idea that even an entrenched consensus was eventually seen for what it was: flawed and based on cherry picked facts. It took a long time though. Nor Yudkin nor Keys lived long enough to see this consensus overthrown.

Does it mean that climate science is wrong because there was this much defended consensus in nutrition science that after half a century turned out to be wrong? Not necessarily. Those two controversies have their similarities, but are logically not related. It is not because there are resemblances between the two that the outcome will be the same. The story just learns us that the ruling consensus can be wrong, even if this specific consensus position is held even for a long time and even if there are checks and balances in place. The consensus position is not the reliable construct that it is painted as.

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