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Michael Mosley talks to two experts who have different opinions on how bad saturated fat is for us.

Saturated fat is found in animal fats – including dairy – and some vegetable oils such as palm and coconut oil. Other vegetable oils, like olive and sunflower, contain polyunsaturated fats which are traditionally thought to be better for us.

What is the debate?

Interest in the link between dietary fats and cardiovascular disease emerged from animal studies conducted in the 1930s. These showed that high cholesterol in the diet causes lesions in their arteries. Researchers then started looking at human diets and the link between saturated fat and heart disease was first shown in humans in the 7 country study’ in 1980.

It followed 12763 men aged between 40-59 and based in 7 different countries (Yugoslavia, Finland, Italy, The Netherlands, Greece, USA and Japan) for 10 years. It found that the highest risk factors for heart disease were age, blood pressure and serum cholesterol concentration which is related to saturated fat in the diet – but although it showed evidence of a link, it could not show that saturated fat caused heart disease.

The countries with low saturated fat intake and low incidence of heart disease were less industrialised and differed in many other ways from the wealthier countries, particularly in physical activity, sugar intake, obesity and, at that time, smoking habits.

What was needed were careful experiments where people changed their saturated fat intake, and when these were done, the evidence suggested that it’s important to replace saturated fat with polyunsaturated fat, rather than simply cut back on fat full stop.

However, at some point this ‘replacement’ advice got corrupted and from the 60s, through the 70s, 80s and 90s, the advice became to cut down on fat generally and particularly saturated fat.

So, with research ongoing – especially into the roles of ‘good’ and ‘bad’ cholesterol and how our diets affect them, what is the best health advice?

Professor Kay-Tee Khaw from the Department of Public Health at Cambridge University was co-author on a recent paper which found no link between saturated fat in the diet and heart disease. However, Professor Christian Drevon from the Department of Nutrition at Oslo University is sceptical about these findings and thinks that saturated fat of all kinds is bad for our health.

Both agree that a lot of saturated fat can be a bad thing, and that polyunsaturated fats are important in the diet. However, whilst Professor Khaw thinks that some kinds of saturated fat – for example that found in nuts, and possibly dairy products, is not bad for us, and may even be good for us – Professor Drevon thinks that all saturated fat should be avoided where possible.

Professor Khaw also raises the interesting point that the fat content of meat changes depending on what the animals themselves were fed – adding another factor to the complexity of the data which hasn’t previously been studied.