Margarine or butter — the story of the advice that flipped

If you grew up in America in the 1970s, '80s, or '90s, you probably remember it: the tub of margarine on the breakfast table. It wasn't there by accident. It was there because it was the responsible choice — the one that school cafeterias, nutrition education, and public health messaging pointed toward. Butter was the old way; margarine was the modern, heart-friendly one.

Then something happened. During the 1990s and 2000s, the tone began to shift. Suddenly voices emerged claiming the opposite: that margarine had been the villain all along, that butter had been wrongfully convicted. Today both narratives live side by side — and for anyone who just wants to spread something on their toast, it's hard to know what actually holds up.

The question 'margarine or butter' is fundamentally a question about fat. Butter consists largely of saturated fat from milk. Margarine is made from vegetable oils, which mostly contain unsaturated fats — but which, in the margarine of earlier decades, were partially hydrogenated to make them spreadable, a process that created so-called trans fats. It's in the difference between these types of fat, and in how our knowledge of them evolved, that the whole story lies.

This article goes deep into that particular story. The broader history of how dietary advice has changed over time — and how to relate to today's recommendations — can be found in our article If dietary advice has changed before — how do we know today's advice is right?

Fat is not a single thing. At the molecular level, fatty acids differ in how their carbon chains are built, and those differences appear to matter for how the body handles them.

• Saturated fat (abundant in butter, cheese, meat) has carbon chains without double bonds. High intake is, in studies, associated with higher levels of LDL cholesterol, a blood lipid marker that in turn is linked to cardiovascular disease risk.
• Unsaturated fat (abundant in vegetable oils, nuts, fish) has one or more double bonds. Higher intake of unsaturated fat in place of saturated fat is, in the research, associated with more favorable blood lipid profiles.
• Industrial trans fat arose as a side effect when liquid vegetable oils were partially hydrogenated to make them solid — precisely the technique that made the margarine of that era possible. Here the science is no longer a question of mere association: the harmfulness of industrial trans fats to the heart and blood vessels is now established knowledge.

It's that last point that makes the margarine-versus-butter story so remarkable. The advice to choose margarine was built on a reasonable hypothesis about saturated fat — but the product itself carried a problem that no one knew about when the advice was given. To understand how that could happen, we need to go back to the 1950s.

Act 1: How margarine became the hero

After World War II, heart attacks rose sharply across the Western world, and researchers searched feverishly for explanations. The American physiologist Ancel Keys formulated a hypothesis that would shape half a century of dietary advice: that saturated fat in the diet raised blood cholesterol, and that high cholesterol was connected to heart disease. In the famous Seven Countries Study (Keys, A. et al., launched in 1958), diet and heart disease rates were compared across seven countries, and the pattern seemed clear — populations that ate a lot of saturated fat had more heart disease.

It's easy in hindsight to sneer at the study's weaknesses — it was observational, the countries were not randomly selected, and the correlation was just that: a correlation. But that is judging the past by the standards of the present. Given the evidence available at the time, the diet-heart hypothesis was a serious and reasonable best guess, and it was supported by the era's physiological knowledge about blood lipids.

The consequence was logical: if saturated fat was the problem, people should swap butter's saturated fat for margarine's vegetable-based alternative. Margarine became the official, modern, and responsible choice. In the United States, it moved into school cafeterias, nutrition education, and everyday life — the American Heart Association itself recommended margarine over butter for decades. The tub of margarine on the breakfast table wasn't carelessness — it was care, built on the best knowledge of its time.

Act 2: The reversal — trans fats

The problem lay not primarily in the hypothesis, but in the product. To make liquid vegetable oil solid and spreadable, partial hydrogenation was used — and that process created industrial trans fats. For a long time, few suspected that this particular detail would prove decisive.

From the 1990s onward, the evidence grew rapidly. Large epidemiological studies and controlled trials pointed in the same direction, and an influential review in the New England Journal of Medicine — Mozaffarian, D. et al. (2006), 'Trans Fatty Acids and Cardiovascular Disease' — summarized the state of the science: industrial trans fats worsen the blood lipid profile in several ways at once (raising LDL, lowering HDL) and are linked to a markedly increased risk of cardiovascular disease, even at relatively low intakes. Here we don't need to hedge: that industrial trans fats are harmful is now established knowledge — so established that the World Health Organization launched the WHO REPLACE initiative in 2018 with the goal of eliminating industrially produced trans fats from the global food supply.

When this knowledge reached the public, the debate turned hard. Margarine, which had been the heart-friendly choice for decades, suddenly stood accused of having contained precisely the type of fat that turned out to be the worst. To many, it felt like a betrayal — and it's in that emotional aftershock that much of today's butter-versus-margarine rhetoric was born.

Here it's important to keep two things separate. The advice to choose the partially hydrogenated margarine of that era was, in hindsight, worse than it needed to be — not because anyone lied, but because the knowledge was incomplete. The effects of trans fats simply weren't known when the advice was formulated. The right conclusion is not that general advice is meaningless, but that better-supported general advice is needed — and that the system actually worked: when the evidence arrived, both the products and the advice changed.

Act 3: Where do we stand today?

Today's margarine is not the margarine of the past. Manufacturing methods have changed, and industrial trans fats are effectively gone from spreads on the American market — in 2015, the FDA determined that partially hydrogenated oils are no longer 'generally recognized as safe,' a decision that effectively phased them out of the U.S. food supply. Judging today's margarine by the recipes of the 1980s is a bit like judging today's cars by cars without seat belts.

And butter? The question of saturated fat is more nuanced than either camp likes to admit. Research continues to suggest that replacing saturated fat with unsaturated fat is associated with more favorable blood lipids and lower cardiovascular risk, which is the basis for the current Dietary Guidelines for Americans. At the same time, scientific discussion is ongoing about how large the effect is, whether different saturated fatty acids differ from one another, and whether the overall dietary pattern matters more than individual foods. The honest conclusion, then, is not 'butter won in the end.' It's that the advice flipped because the knowledge changed — and the knowledge continues to be refined.

That's the whole point of the story: how do we know where we stand now? The short answer is that we never know with complete certainty — but today's evidence base is broader, the methods better, and the self-scrutiny greater than in Keys' day. How to relate, as an individual, to advice that shifts is something we've written about at length in If dietary advice has changed before — how do we know today's advice is right?

This article won't tell you what to spread on your toast — for current dietary recommendations, we refer you to the Dietary Guidelines for Americans (USDA and HHS). But the story of margarine offers some useful ways of relating to shifting advice in general:

• Separate the product from the principle. The advice 'more unsaturated, less saturated' and the product 'partially hydrogenated margarine' were two different things. The principle has held up better than the specific product. Many people find it easier to navigate when they ask what principle a piece of advice rests on.
• Be skeptical of total reversals. When someone claims that 'everything we believed was wrong,' reality is usually more nuanced. Knowledge is refined gradually — it is rarely discarded wholesale.
• Watch out for outdated arguments. Arguments against today's margarine that are based on trans fats target a product that no longer exists on American grocery shelves. Check what era an argument is actually describing.
• The whole appears to outweigh individual choices. Research points toward the overall dietary pattern being more strongly associated with health outcomes than any single table spread. Many people find that liberating: the choice between butter and margarine is likely not the most important choice you make in a day.
• No guilt in hindsight. Anyone who chose margarine in the '80s made the responsible choice based on the knowledge of the time. That the knowledge later grew is not an individual failure — that's how science works.