Yudkin argued that excess sugar was causing health problems. Keys argued that sugar was not the problem, the consumption of fat was causing health problems. Keys was effective at loudly denouncing anyone who criticized his fat hypothesis.

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.

Source: The Sugar Conspiracy

The propaganda messaging was intense.

Keys, and especially government and later media proponents relied on many methods of propaganda:

• Appeal to authority
• Name calling and ad hominem attacks
• Transference
• Assertions

And not surprisingly, a large dose of arrogance.

Today we see that this simplification led to decades of official government nutrition advice that was wrong and not supported by evidence. The government’s new nutrition guidelines, when they first arrived in about 1980, were seen as so important that employers held sessions for employees where nutritionists and dieticians would tell us of the need to eliminate fat from our diets. Literally, to use as little fat as possible, as close to zero as possible. One attendee sitting behind me raised his hand and asked, “So except for diabetics and tooth decay, you are saying that sugar is not a problem?” The answer from the professional nutritionist was yes, sugar was not a problem. Media bombarded us with similar messages – with stories emphasizing the need to remove fat from our diets and to discontinue eating eggs. We were to switch to eating far more carbs (60% of our diet should come from grains, they said), “lean” meats stripped of fat, and fat free dairy products.

Social media, in spite of its numerous problems, also provides a counter effect when experts go off the rails:

It is a familiar complaint. By opening the gates of publishing to all, the internet has flattened hierarchies everywhere they exist. We no longer live in a world in which elites of accredited experts are able to dominate conversations about complex or contested matters. Politicians cannot rely on the aura of office to persuade, newspapers struggle to assert the superior integrity of their stories. It is not clear that this change is, overall, a boon for the public realm. But in areas where experts have a track record of getting it wrong, it is hard to see how it could be worse. If ever there was a case that an information democracy, even a very messy one, is preferable to an information oligarchy, then the history of nutrition advice is it.