A large study appears to confirm the long-held view that eating high amounts of saturated fat increases the risk of premature death.

This US study is the most detailed investigation into the impact of dietary fats on health ever undertaken. According to the researchers, in recent years, there has been ‘widespread confusion in the biomedical community and the general public about the health effects of specific types of fat in the diet'.

"This study documents important benefits of unsaturated fats, especially when they replace saturated and trans fats," they said.

The study looked at over 126,000 people who had taken part in two long-term studies, which involved them being surveyed every two to four years about their health for up to 32 years.

During the study period, more than 33,000 people died and the researchers looked at the relationship between these deaths and the types of fats in the participants' diets.

The study found that different types of fat had different links with mortality. The biggest impact was seen with trans fat.

Trans fats are artificially produced fats that are used in many processed foods, from fried foods to biscuits and ready-meals.

The researchers found that every 2% higher intake of these fats was linked with a 16% increased chance of a premature death during the study period.

People who consumed higher amounts of saturated fats also faced a higher risk of death. When compared with the same number of calories from carbohydrates, every 5% rise in saturated fat consumption was linked with an 8% increased risk of death.

However, consuming high amounts of unsaturated fats was linked with lower mortality. Those who ate high amounts of polyunsaturated and monounsaturated fats had an 11-19% reduced risk of death compared with the same amount of calories from carbohydrates.

Among the polyunsaturated fats, omega-3 fatty acids, found mainly in fish oils, and omega-6, found in most plant oils, were linked with a reduced risk of premature death.

The study noted that the impact of different types of fats depended on what people were replacing them with. Those who replaced saturated fats with unsaturated fats significantly reduced their risk of death, especially if they replaced the saturated fats with polyunsaturated fats.

Those who replaced saturated fats with carbohydrates reduced their mortality risk, but only by a very small amount.

"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," commented the study's senior author, Prof Frank Hu, of Harvard Medical School.

Details of these findings are published in the journal, JAMA Internal Medicine.