Olive Oil
Unsaturated fats from olive oils are associated to lower premature mortality levels. USDAgov/Flickr

Unsaturated fats are not bad for you – they could in fact be associated to a lower mortality, scientists have said. In the largest and most detailed examination to date on how dietary fats impact health, they have shown that replacing some of the saturated fats in your plate, like butter, by unsaturated plant-based fats, like olive or soybean oil, was likely to yield long-term health benefits.

The study, published JAMA Internal Medicine, looks at data gathered over three decades, suggesting that higher consumption of saturated and trans fats was linked with higher mortality, compared with the same number of calories from unsaturated fats.

This supports the idea that the types of fat rather than the total amount of fat in the diet influences the development of diseases.

'Good fats'

The scientists collected data from two large-long term population studies - the Nurses' Health Study and the Health Professionals Follow-Up Study – which included more than 126,000 participants followed over 32 years. In that period, some 33,000 deaths occurred.

The researchers looked at participants' answers about their diet and investigate the relationship between these deaths and the amounts and types of fats consumed by people. They also looked at the causes of death among participants, identifying those due to cardiovascular disease (CVD), cancer, neurodegenerative disease, and respiratory disease.

Butter knife
People could benefit from replacing butter by vegetable oilRenee Comet National Cancer Institute

The researchers discovered that trans fats had the worse effect on the health of individuals, with 2% higher intake of trans fat was associated with a 16% higher chance of premature death overall.

Eating saturated fats was less risky but still associated to early mortality – every 5% increase in saturated fat intake was associated with an 8% higher risk of overall mortality. These findings strongly suggest that it is the type of fat and not the quantity consumed which is associated to higher risks of poor health and death.

Furthermore, the scientists show the consumption of some 'good' unsaturated fats is statistically correlated with lower mortality – omega 3 in fish and soy and omega 6 in plant oils were particularly beneficial.

Replacing your fats

Another key finding is that replacing saturated fats with unsaturated fats can prevent people from developing diseases and dying prematurely. The scientists discovered that people who replaced saturated fats with unsaturated fats had significantly lower risk of death overall.

This association was also true when they looked at specific causes of death: people who ate unsaturated fats instead of saturated fats had a lower risk of death from CVD, cancer, neurodegenerative disease, and respiratory disease, compared with those who maintained high intakes of saturated fats.

"Our study shows the importance of eliminating trans fat and replacing saturated fat with unsaturated fats, including both omega-6 and omega-3 polyunsaturated fatty acids. In practice, this can be achieved by replacing animal fats with a variety of liquid vegetable oils," concludes Frank Hu, senior author of the study.