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.  

What are butter and margarine?

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.

During World War Two, most margarine was made from vegetable oils that had been hardened via hydrogenation (Credit: Getty Images)

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.

Breaking down the fats

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 join 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.

Saturated fat from butter may not be as heart-healthy as the saturated fat found in fermented dairy products, including yoghurt (Credit: Getty Images)

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.

"This made us think: could it be that nutrients alone are unhelpful to look at in isolation?" says Forouhi. "Could we say that, if saturated fat is coming from dairy or fish, it is different than saturated fat from meat [for example]?"

Forouhi went on to discover that saturated fat from meat and butter is related to a higher risk of heart disease compared with fat from fish or fermented dairy products, such as yoghurt.

"Foods are way more than sum of their nutrient parts," she says. "They have macronutrients, loads of different micronutrients, minerals vitamins, fibre, salt, additives, and some are fermented."

Ultra-processed foods

While butter is considered a "processed culinary ingredient", margarine is an ultra-processed food, according to the most-used classification system of processed foods.

Numerous studies have linked ultra-processed foods with poor health outcomes including obesity, type 2 diabetes and heart disease. However, there's no long-term evidence specifically comparing the health effects of butter and margarine. This is partly because some studies looking into the effects of different foods on our health group butter and margarine into one food type, along with other foods.

One study, for example, found that "spreads" are associated with an increased risk of developing type 2 diabetes, but research will need to be more detailed than this, says Melissa Lane, a postdoctoral research fellow at Deakin University in Australia.

One way to do this is with a method called "substitution analysis", where margarine is substituted with a non-ultra-processed alternative, with equal number of calories, Lane says.

"We need more research to compare sub-groups of ultra-processed foods directly with non-ultra-processed alternatives and the results may differ depending on the health outcome under investigation," she says.

"Margarine has the better nutrient profile in terms of being lower in saturated fat than butter, and both should be considered in the context of the whole diet," she says. "But emerging evidence suggests that there's an association between poor health and ultra-processed diets above and beyond nutrients."

Also, Lane says, you might want to opt for less processed alternatives such as olive oil, which contain beneficial mono- and polyunsaturated fats, and aim to reduce overall ultra-processed food intake without focusing too much on specific foods.

While there's a lot of research showing the negative impacts of diets high ultra-processed foods on our health, the counter-argument is that some of these foods still contain some nutrients that have benefits. For example, margarine provides some nutrients, including vitamin A.

"Wholegrain bread bought from the store is probably classified [as a] UPF," says Harnack. "Breakfast cereals are mostly ultra-processed, even though they're a great source fibre. The science isn't there to back up making a carte blanche recommendation to avoid all ultra-processed foods," she says.

Diets rich in polyunsaturated fats such as olive oil are thought to help reduce the risk of heart disease (Credit: Getty Images)

Margarine versus butter: the final stand-off

There's less evidence showing the effects of margarine on our health because, while the nutrient profile of butter varies very little from country to country, margarine has a broader definition, and has changed over time, says Forouhi. And when researchers carry out long-term studies, they analyse people's dietary patterns over decades.

But while there's a lot less research into margarine, Forouhi adds, foods with less saturated fat, higher in polyunsaturated fats and with no trans fats are the best option.

It's our long-term diet patterns that really matter, experts say, and our overall consumption of saturated fat over weeks and months.

"The bottom line is that it depends how much of it you have. If you're scraping a rich-tasting butter onto toast once a week, and the rest of your diet is healthy, it probably doesn't matter," says Collins. "But this isn't what most people eat," she says. "People have diets dominated by energy-dense, nutrient-poor food. You just have to walk into any supermarket at look at the number of things that are pre-packaged. We're not cooking from scratch, or buying as much fruit and vegetables, so we don't realise that our fat intake is as high as it is," says Collins.

What spread you choose, Collins adds, should be based around your own personal health needs. "You almost have to be detective to work out which is best for you. Think about your main health needs and line up all the labels of the spreads you normally select from and compare," she says.

One advantage of margarines over butter, Collins adds, is that it's easier to use less of spreads. "You just about have to get [a] jackhammer for high-fat butter from the fridge, and you end up with huge chunks on your bread," she says.

Ultimately, which spread you chose is just one piece of the overall nutritional puzzle. In other words – it may be that what you're putting your spread on is more important. "If you're putting butter on a corn-on-the-cob, rather than a croissant, it's a completely different meal," says Collins.