It wasn’t that long ago that the closest most Britons got to a coconut was at the fairground or on the inside of a Bounty bar. Yet in the past three years, this hard, hairy drupe (that’s the official term) of the coconut palm tree has emerged as the latest “superfood” extolled by celebrities and health food shops for its nutritional, healing and mind-enhancing powers.

Aisles of health food shops are packed with bags of flour, snacks, milk, sugar and drinks made from its meat and milk. And leading the way is coconut oil, a sweet smelling, greasy fat used for frying, baking, spreading on toast, adding to coffee or simply rubbing into your skin.

It’s hard to exaggerate how much hype surrounds coconut oil on health food websites, blogs and YouTube channels. Wellness Mama lists 101 uses including as a mental stimulant, hair conditioner and treatment for insomnia, heartburn, cuts, acne, haemorrhoids, mosquito bites and sunburn. Everdine recommends using coconut oil “to cook with at every meal due”, while Holland & Barrett claims “coconut oil is very healthy”, adding: “Coconut oil is the little black dress of wellbeing – everyone should have some!”

Sites such as these, along with celebrity endorsements from the likes of Gwyneth Paltrow and Kourtney Kardashian, have helped UK sales of coconut oil rise over the past four years from around £1m to £16.4m last year, according to consumer research group Kantar.

When it comes to superfoods, coconut oil presses all the buttons: it’s natural, it’s enticingly exotic, it’s surrounded by health claims and at up to £8 for a 500ml pot at Tesco, it’s suitably pricey. But where this latest superfood differs from benign rivals such as blueberries, goji berries, kale and avocado is that a diet rich in coconut oil may actually be bad for us.

Coconut oil is deficient in the essential fatty acids, which makes it much worse than lard or palm oil Professor Tom Sanders, King's College London

Earlier this month, the American Heart Association (AHA) warned that coconut oil contains the same level of saturated fat as beef dripping. In fact, it’s so oozing with artery-clogging saturated fat that lard is a healthier option.

The AHA alert, which has followed similar observations from scientists over the years, has triggered an online battle between those who claim the science of coconut oil is more complex and more sophisticated than food scientists acknowledge and those who say food faddists have been duped by clever marketing.

So who is right? Even if coconut oil really is full of saturated fats, are all saturated fats bad? And why do we get such conflicting messages about the fat in our diet?

Coconut oil is pressed from the meat of a coconut. It has been used in Africa, Asia and South America for centuries and was routinely used in American processed food in the middle part of the 20th century. In the 1940s, it was the main source of non-dairy fat in the US diet until it was replaced by vegetable oils, particularly soya bean oil. Concerns about its high saturated fat content emerged in the middle of the last century and are rife today, even as the oil makes a revival among health food lovers.

Priya Tew, spokesperson for the British Dietetic Association, says: “Coconut oil is a high saturated fat. It’s about 92% saturated fat – so more than lard or butter. If a woman has two tablespoons, she is eating 20g of saturated fat, her recommended daily amount.”

In the long-established pecking order of fats laid down over many years by public health officials, trans fats are classed as the least healthy. The chemical transformation makes them hard for our bodies to process. They raise levels of bad (LDL) cholesterol and lower good (HDL) cholesterol, increasing the risk of developing heart disease and strokes; they are also linked to type 2 diabetes. In contrast, unsaturated fats are pretty universally accepted as beneficial because they raise levels of good HDL cholesterol. That leaves saturated fats somewhere in the middle.

Since the 1970s, the message from public health bodies has been that they raise bad cholesterol, fur up arteries and increase the risk of strokes, heart disease and heart attacks. That’s the view of the UK government, the World Health Organisation and virtually every other public health body in the world. So where does the idea of coconut oil, one of the richest sources of saturated fat available, being a health food come from?

One branch of evidence often cited by the pro-coconut oil lobby is work done by Dr Marie-Pierre St-Onge, associate professor of nutritional medicine at Cornell University Medical School, in the early 2000s. Her team was looking at the impact on health of medium-chain triglycerides (MCTs), a form of fat molecule that has shorter chains of fatty acid than most and which is found in coconut oil in higher concentrations than any other natural food.

In 2003, her team published research comparing the effects of diets rich in MCTs or long-chain triglycerides (LCTs) on 24 overweight men. She found that eating more MCTs over the month-long study led to losing an extra pound in weight compared with those eating a similar amount of LCTs. Further studies had similar findings. In 2008, she showed that a diet containing MCTs led to more weight loss than a similar diet containing olive oil.

It was a fascinating result and a reminder that not all saturated fats are the same. And it was leapt upon by coconut oil supporters. Holland & Barrett’s website, for instance, claims that the majority of fat in coconut oil is made up of MCTs. But the link from these studies to coconut oil was arguably a leap too far. Recent studies suggest that coconut oil actually comprises just 13-15% MCTs. The rest are traditional LCTs.

“From what I can tell, my research is being used to say that coconut oil is healthy, but this is a very liberal extrapolation of what we’ve actually studied,” says Dr St-Onge.

In her tests, volunteers were given a concoction made from 100% MCTs.

“We don’t know if the amount in coconut oil is sufficient to have similar effects as pure MCT oil in releasing energy expenditure and improving satiety and weight management. From recent studies, it seems that it is not.”

Coconut flesh, to be made into oil, drying in Papeete, French Polynesia. Photograph: Gregory Boissy/AFP/Getty Images

If there’s little evidence that coconut oil is less fattening than other saturated fats, what about another often made claim – that it lowers levels of harmful cholesterol? Some studies appear to show that people who eat more coconut in their diets have higher levels of HDL cholesterol – the “healthy” version linked to lower rates of strokes and heart disease. One reason for this cholesterol boost is likely to be the high level of a substance called lauric acid in coconut oil. A meta-analysis of 60 trials in 2003 found lauric acid increased good HDL cholesterol.

But before you are tempted to celebrate by smearing some coconut oil on toast, there’s a caveat. The same analysis found it also raised harmful LDL cholesterol. And there’s little evidence that the rise in good cholesterol from eating coconut oil outweighs the rise in the bad stuff.

There is nothing unusual about coconut oil in this respect – all saturated fats raise both good HDL and bad LDL cholesterol levels. What seems to matter is the ratio of these two types of cholesterol in our blood. So while Lauric acid may raise good cholesterol, the increase could be offset by a rise in the bad stuff.

There’s an added complexity. Tew points out that not all HDL cholesterol is necessarily good. As the science of cholesterol is explored in more detail, researchers are discovering that some types of HDL are protective, while others are “non-functional’’ and do nothing for the heart. She suspects that some of the rise in good HDL associated with lauric acid may be an increase in the non-functional type of cholesterol, which, while looking good on paper, won’t protect us from heart attack or stroke.

The presence of this non-functioning HDL cholesterol and the rise in bad cholesterol when we consume lauric acid could help to explain other studies that show lauric acid in our diets as being associated with an increased risk of heart disease.

It’s not just the claims about weight loss and cholesterol that don’t stack up. A paper in the British Nutrition Foundation’s Nutrition Bulletin last year concluded that there is simply not enough evidence for any health claim based on coconut oil.

Dr Stacey Lockyer and Dr Sara Stanner of the BNF wrote: “Claims relating to potential health benefits of coconut oil are often based solely on animal or in vitro studies or human studies feeding one component of coconut oil rather than the whole food.’’

There is, for instance, no good evidence that it helps boost mental performance or prevent Alzheimer’s disease, they say.

The theory is that the fat in coconut oil metabolises more quickly than other fats because of the high MCT content. The argument goes that the brain cells of people with Alzheimer’s disease are unable to use glucose properly and so starve. Coconut oil is an easier to use source of energy and so keeps brain cells going. It’s an interesting idea, but not one based on evidence, according to the Alzheimer’s Society. A clinical trial into the potential impact was discontinued because there were not enough people taking part.

Coconut oil is also said to be a good source of antioxidants. Although this is true, it’s nowhere near as good as fruit and vegetables. Tom Sanders, emeritus professor of nutrition and dietetics at King’s College London, says: “It is a poor source of vitamin E compared with other vegetable oils. Coconut oil is also deficient in the essential fatty acids, which makes it much worse than lard or palm oil.’’

As for it’s much touted antimicrobial qualities that help restore gut bacteria, there’s virtually no evidence either way. For Tew, the coconut oil issue is another example of the perils of classifying some foods as superfoods. She, like most dietitians, believes it’s an unhelpful concept, used by marketers. Labelling products as superfoods can fool people into thinking they are eating well when they are not. Munching a handful of goji berries after fried steak and chips won’t make the meal healthy.

The obsession with expensive, exotic superfoods also means we forget the easy, cheap foods that are more likely to keep us healthy – apples, oranges, broccoli and milk. But if canonising foods is unhelpful, then perhaps so is demonising them. And here, public health officials may have been guilty of oversimplification – and an unfair assessment of fats. In the past few years, the debate over whether fats have been wrongly turned into villains has become intense and polarised.

At one extreme are cardiologists such as Dr Aseem Malhotra, who last year told the media, during the launch of a controversial National Obesity Forum report into fat: “Eat fat to get slim. Don’t fear fat. Fat is your friend.”

But even more moderate voices acknowledge that the low-fat diet health message is too crude – and not always supported by the evidence. One of the best studies into saturated fats and heart disease was a Cochrane review of 15 clinical trials covering 59,000 people, which found that cutting out saturated fat and replacing it with carbs and proteins made no difference to cardiovascular disease. Yet when the saturated fats were replaced with unsaturated fats, there was a 27% drop in heart disease.

It seemed to be showing that saturated fats are no worse for us than carbs – but that the real benefits come when we swap them for olive oils, nut oils and the fats in avocado.

Sanders believes not all saturated fats are the same. “It is nuanced and it depends where they come from,” he says. “A high intake of processed and red meat is associated with an increased risk of heart disease, but dairy seems to be quite neutral. Dairy provides other things – magnesium, calcium and nutrients that may counteract the effects of saturated fat.”

But while not all fats are equal, Sanders, like most food scientists, remains unconvinced by the health claims for coconut oil or the suggestion that the saturated fat in coconut oil is less harmful than other saturated fats. There is, he says, insufficient evidence for such claims.

“There is an incredible amount of hype around the coconut that is driven by marketing, not science,” he adds.

Christine Williams, professor of human nutrition at the University of Reading, agrees.

“There is very limited evidence of beneficial health effects of this oil – and marketing has won out over science again,” she says.

Coconut oil may be no superfood, but equally, it is no villain. What it is is a reasonable tasty if overpriced occasional alternative to other – equally unhealthy – saturated fats and one that, unusually, you can rub into your face without smelling like a butcher’s shop or cheese counter. But if you’re after a miracle cure for obesity, insomnia or piles you’ll probably have just as much success with a Bounty bar.

David Derbyshire is a former Daily Mail and Daily Telegraph science correspondent. He has written for the Observer on acupuncture, mindfulness and the science of wine-tasting

Coconut claims debunked

According to health food websites, coconut oil can be used to treat everything from thyroid disorders to thrush, via brittle bones and dementia. But in a recent report, the British Nutrition Foundation said: “There is no strong scientific evidence to support health benefits from eating coconut oil.” So where has this idea come from? Coconut oil advocates believe that it has powerful antibacterial and anti-inflammatory properties because it contains lauric acid, a fatty acid also found in breast milk. It is true that lauric acid derived from coconut oil acts as an antibiotic, but this has only been seen in vitro and at super-concentrated doses. So while lauric acid can kill bacteria, it seems coconut oil can’t. In studies where the two have been directly compared, coconut oil was shown to be as useful as water at killing bacteria. Here are three more of the most commonly cited, scientifically dubious health uses for coconut oil to be wary of. Agnes Donnelly

Photograph: Alamy

Skin

While it is true that coconut oil is found in many sunscreens, coconut oil on its own has an SPF of around 1. The NHS recommends that when you are in the sun you should be using a sunscreen with SPF 15 at the very least. Therefore coconut oil alone is not going to be enough to protect your skin from the sun’s UV rays, a major cause of skin cancer.

Photograph: Alamy

Hair

Coconut oil is believed to moisturise, provide nutrients, kill bacteria and improve circulation of blood in the scalp. Some websites even promote it as a way to slow hair loss. In truth, coconut oil contains tiny amounts of nutrients and its antibacterial properties are unproved. Any effect it has on your hair is purely cosmetic.

Photograph: Alamy

Health

‘Pulling’ is a practice where people swill liquid oil around their mouths for up to 30 minutes because they believe it draws harmful bacteria and toxins out of their mouth. There is no evidence that this works. However, there have been cases of lipoid pneumonia, when the oil is accidentally inhaled into the lungs and causes disease.

Know your fats…

Dietary fat can be divided into two camps – the solid, mostly animal-derived saturated fats such as lard, dripping and butter and the liquid, unsaturated fats such as olive oil and nut oil, mostly derived from plants.

We are so used to bandying around words such as saturated and trans fat that many of us (or at least those of us without a chemistry A-level) rarely consider what the words mean.

Whether a fat is saturated or unsaturated depends on the way that carbon atoms in the long chains of fatty acids found in fat molecules are connected to one another.

In an unsaturated fat molecule, one or more carbon atoms are linked by double bonds. If the circumstances are right, one of these bonds can loosen and connect to a passing hydrogen atom, adding another hydrogen atom to the molecule. However, in a saturated fat such as lard, all the carbon atoms are held together with single bonds. There is no spare capacity for the fat molecule to take on any more hydrogen atoms and so the fatty acid is said to be “saturated” with hydrogen.

The ability of unsaturated fats to take on hydrogen atoms is exploited when vegetable oils are “hydrogenated” – converted into solid trans fats by exposing them to hydrogen gas and a catalyst. Trans fats are cheaper than normal saturated fats, more suitable for industrial scale baking and have a longer shelf life.

A fat is monounsaturated if it contains just one double bond among its carbon atoms. If it has many double bonds, it is polyunsaturated.