Butter versus margarine: which is the healthiest spread?

Butter is high in saturated fat – but margarine is an ultra-processed food. Disentangling which is the queen of healthy spreads is extremely tricky.

Butter has been a staple in the British diet for centuries, long before margarine came on the scene in the early 20th Century.

However, in the middle of the 20th Century, people started replacing butter with margarine, due to the growing consensus that all fats were bad for our health. The food industry responded by producing low-fat versions of many of our diet staples, and dietary guidelines told people to reduce their fat intake.

Soon after, attention narrowed in on saturated fat, rather than all types of fat.

"From the 1950s, the concept slowly emerged that saturated fat was the bigger culprit and should be replaced with polyunsaturated fat," says Nita Forouhi, professor of population health and nutrition at the University of Cambridge.

Now, the tide is turning once again. In Australia there's been an uptick in eating butter in recent years compared with margarine, says Clare Collins, laureate professor in nutrition and dietetics at Newcastle University in Australia. "There's a lot of confusion around butter, including fat types, so maybe people have gone back to eating what they like the taste of more. But it helps if people understand what research is saying," she says.

As it happens, the research has been saying a lot. Scientists have been investigating the health benefits and costs of various spreads for decades. And when it comes to butter and margarine, there's a lot to unpack.  

To make butter, first milk is heated, then spun around to separate the cream from the milk. This cream is then cooled, then churned, and the buttermilk – the liquid remaining once the solid butter has been separated – is removed. Salt is sometimes added to the remaining butter mixture.

Margarine is made by beating oil with water to form a solid product, before several other ingredients are added, such as emulsifiers and colouring.

Historically, margarine producers added hydrogen to margarine to convert liquid oils into solid fats, and make them more spreadable. But soon they realised this created "hydrogenated" or "trans" fats – a kind of unsaturated fat that as become notorious for its poor health consequences, such as coronary heart disease.

Researchers have shown that a diet high in man-made trans fats increases bad LDL cholesterol and reduces good HDL cholesterol, which leads to an increased risk of heart disease, says Lisa Harnack, professor of nutrition at the University of Minnesota in the US. In fact, trans fats have an even worse effect on cholesterol than saturated fat, she says.

Trans fats are a form of unsaturated fat – but research shows a diet high in trans fats is linked to the worst health outcomes.

Saturated fat is made up of molecules of fatty acids without any double bonds that can be broken to with other molecules, whereas polyunsaturated fats and monounsaturated fats do have those double bonds. And there are numerous types of saturated fats, such as small, medium, and long-chain saturated fats, and different types of polyunsaturated fats.

"The general principle is that foods high in saturated fats are more likely to raise blood cholesterol if you've already got heart disease, high cholesterol or other risk factors for heart disease," says Collins. According to one estimate, trans fats may be responsible for 540,000 deaths each year.   

But for the general population, the idea that changing to a low-fat diet can reduce heart disease has been questioned in recent decades. In fact, large trials have shown the opposite effects of a diet high in certain high-fat foods such as nuts and extra virgin olive oil, which are both high in polyunsaturated fat.

"We shouldn't be worried about total fat so much, it's the proportion of fats within that that matters," says Forouhi.

Specifically, of the three types of fats we eat – saturated, monounsaturated and polyunsaturated – we should be aware of how much saturated fat we're eating, she says. The general guidance is that saturated fat makes up no more than 10% of our total energy. But it's more complicated than this.

"There's now increasing recognition that saturated fat isn't just one homogenous thing. It's made up or individual fatty acid chains and chain lengths defined by the number atoms in the chain, which gives each individual fatty acid different properties, and different impacts on health," says Forouhi.

Forouhi has found through her research that saturated fatty acids with an odd number of carbon atoms (15 or 17) are related to lower cardiometabolic risk – the risk of developing type 2 diabetes and heart disease). Meanwhile, those with an even number of atoms in the chain (16 and 18) are associated with an increased cardiometabolic risk. And Forouhi has found that fatty acids with 15 and 17 carbon atoms are typically representative of dairy foods.

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