Researchers say diets with a high level of saturated and trans-fat increases will shorten a person's life after a major US study.

Clear evidence that eating the wrong kind of fat can shorten your life has emerged from a major study in the US.

Higher consumption of saturated andt trans-fats was associated with a greater risk of early death, the scientists found.

In contrast, people whose diets were rich in polyunsaturated fatty acids (Pufa) and monounsaturated fatty acids (Mufa) - the kind of fat obtained from plant foods, vegetable oils and fish - had a reduced risk.

Saturated fat chiefly comes from animal sources such as red meat and dairy products, while trans-fats are mostly derived from processed oils.

Replacing five per cent of calories from saturated fats with the equivalent amount of energy from Pufa and Mufa was associated with a 27 per cent and 13 per cent lower likelihood of death respectively.

The researchers analysed data from more than 126,000 men and women in two large study groups whose progress was followed for up to 32 years.

Dietary fat intake was assessed on recruitment and updated every two to four years.

Participants in the study were split into five groups ranging from low to high consumption of different kinds of fat.

Over the study period, a total of 33,304 deaths were recorded.

Writing in the journal Jama Internal Medicine, the authors led by Dr Frank Hu, from the Harvard T H Chan School of Public Health in Boston, concluded: "Replacement of saturated fats with unsaturated fats can confer substantial health benefits and should continue to be a key message in dietary recommendations."

British expert Dr Ian Johnson, from the Institute of Food Research, said: "The findings indicate that diets containing relatively high levels of saturated fat were associated with higher mortality compared to diets richer in unsaturated fats.

"Remarkably, replacing only five per cent of total calorie intake from saturated fat (around 15g) with the same quantity of polyunsaturated fat was associated with a 27 per cent lower risk of death from heart disease, cancer and other causes.

"These findings are consistent with current public health recommendations in the UK and elsewhere, and particularly with the concept of a beneficial Mediterranean-style diet, rich in unsaturated fats from plants, fish and olive oil."