Hot on its heels came a new book by a celebrity chef recommending we cook with butter or coconut oil but not olive oil which 'becomes oxidised when heated'.

After decades of being told to avoid butter because of its saturated fat content, why is it being hyped as a health food?

It's a question I asked nutritionist Rosemary Stanton, not just because she's a wise voice on food and health but because she's been known to spread (a little) butter on bread herself.

But in terms of health benefits butter doesn't get Stanton's stamp of approval. Although some recent analyses of observational studies suggest that total intake of saturated fat may not correlate with heart disease, that's not the same as saying that saturated fat is heart healthy, she says.

"Saturated fat has not turned into a saint. It's just that the studies that have concluded  that reducing saturated fat doesn't stop  heart disease haven't looked at what people are eating instead of saturated fat, " she explains.

"If you replace saturated fat with monounsaturated fat  (such as olive oil) or polyunsaturated fat (such as safflower oil) there's an advantage for heart health but  instead  people have reduced some sources of fat but substituted low fat processed sugary foods  – like yoghurt and low fat salad dressings with added sugar.

Increasing refined sugars and starches wipes out any benefits of reducing saturated fat. This is why some analyses of the data show little difference in cardiovascular disease," she says.

Another reason why research in this area is often conflicting is that the focus is often on the type of fat people are eating, but not the food that it comes in – and that's no way to judge  the quality of any diet, Stanton adds.

"There's the same amount of saturated fat in 35g of cheese, 35g of white chocolate, 70g of potato crisps, 90g of roasted cashews, a small (145g) rump steak, and a smallish custard tart. 

Another example is that monounsaturated fats are the main fat in eggs, almonds, avocado, chocolate chip muesli bars and chicken nuggets. It would be nonsense to assume these foods are nutritionally equivalent, yet this is what happens if they're judged solely on their content of saturated or monounsaturated fat."

But even though research into the health effects of saturated fat is inconsistent, there's no evidence that adding saturated fat to the diet has health benefits and that goes for coconut oil too, she says.

Much of the enthusiasm for coconut oil is because, unlike most other saturated fats, it's high in a fatty acid called lauric acid which helps raise 'good' HDL cholesterol.

But without more research it's not clear whether this makes coconut oil heart healthy because lauric acid also raises 'bad' LDL cholesterol, Stanton explains.

"Studies  of people in Samoa and the Cook Islands from the 1960s found that although people ate diets  high in coconut they had  little heart disease – but  along with coconut  oil  they ate a limited diet based on a few staple foods like fish, taro, breadfruit and  bananas and  no processed food.

They also ate the coconut flesh, not just the oil – that's very different to saying you can add coconut oil to a typical western diet and get a benefit," she says.

So while we wait for science to back up the claims for coconut oil and unravel the complexities of fat and heart disease it might make sense to stick with what we really do know – that many studies have found that olive oil, especially extra virgin olive oil, is heart healthy and that unlike coconut oil which raises 'bad' LDL cholesterol, olive oil lowers it.

Should we avoid heating olive oil in case it oxidises and forms harmful free radicals? No, says Dr Catherine Itsiopoulos, Associate Professor in Dietetics and Human Nutrition at La Trobe University and author of The Mediterranean Diet. Although saturated fats like butter are more stable and less readily oxidised when heated, it's also true  that olive oil is rich in oleic acid which is more stable on heating than polyunsaturated fats like safflower or sunflower oil, she explains.

"Olive oil, especially virgin olive oil, is also rich in antioxidants which further protect the oil from becoming oxidised. Olive oil has a reasonably high smoking point so it's fine for frying," she says. "However, some of the more expensive 'boutique' olive oils can contain olive particles which can burn on frying causing a bitter taste."

As for including some butter or coconut oil, Stanton believes that a healthy diet can cope with a little of these fats.

"I eat a little butter not because I think it has any health benefits but because I like it and I think that in the context of an otherwise healthy diet that's fine," she says.