Is the advice to switch to ‘good fats’ bad for you?

By Lilian Anekwe

BMJ Group News

What do we know already?

For many years, advice and guidelines on healthy eating have encouraged us to cut down and, if possible, eliminate saturated fats from our diet. Saturated fats are those found in some margarines and foods containing animal fats like butter, cheese, and lard. It’s been recommended that we replace saturated fats with vegetable fats and oils, such as olive and sunflower oils, which are rich in substances called polyunsaturated fatty acids. Some research suggests these polyunsaturated fatty acids could lower the risk of heart disease.

In recent years, researchers have come to understand that there are lots of different kinds of polyunsaturated fatty acids, and each has its own properties that may have different effects on heart disease risks. Some might have benefits while others might not; we don’t know if the benefits of one or some polyunsaturated fatty acids apply to all.

In this study, researchers looked closely at the effects of swapping saturated fats with one polyunsaturated fatty acid called omega 6 linoleic acid. They did this by looking at a good-quality study that was done some years ago, between 1966 and 1973. The study included 458 men aged between 30 and 59 years old who’d recently had heart problems, such as a heart attack or chest pain (angina). The men were randomly chosen to be in one of two groups. One group reduced the proportion of saturated fats in their diet and increased the proportion of safflower oil, which is around 75 percent linoleic acid. The other group did not change their diet. The researchers then looked at how many men died during the study overall, and from heart and circulation problems in particular.

What does the new study say?

Men who cut saturated fats out of their diet and used more safflower oil were 62 percent more likely to die, of any cause, than men who didn’t change their diet. They were also 70 percent more likely to die of cardiovascular disease and 74 percent more likely to die of coronary heart disease.

Overall, 18 in 100 men who swapped fats died during the study, compared with around 12 in 100 who didn’t change their diet.