Fat goes from zero to hero while carbs are the new villain, according to a large international medical study.

Health experts have controversially called for an overhaul of dietary guidelines after a large international study found a diet high in carbohydrate is associated with greater risk of premature death, not a diet high in fat.

A study of more than 13,500 people from 18 countries, published in the respected medical journal The Lancet, found diets high in carbohydrates were associated with a 28 per cent higher risk of death, compared to low carbohydrate diets.

Diets with a high total fat intake were associated with a 23 per cent lower risk of death, compared to low fat.

"Total fat and types of fat were not associated with cardiovascular disease, myocardial infarction, or cardiovascular disease mortality, whereas saturated fat had an inverse association with stroke. Global dietary guidelines should be reconsidered in light of these findings," the authors concluded.

The current guidelines recommend that 50-65 per cent of a person's daily calories come from carbohydrates, and less than 10 per cent from saturated fats.

The study found the average global diet consisted of at least 60 per cent carbohydrate.

In light of the findings, lead author Dr Mahshid Dehghan at McMaster University, Canada would like the carbohydrate recommendation reduced.

"The current focus on promoting low-fat diets ignores the fact that most people's diets in low and middle income countries are very high in carbohydrates, which seem to be linked to worse health outcomes," Dr Dehghan said.

"A certain amount of carbohydrate is necessary to meet energy demands during physical activity and so moderate intakes, of around 50-55 per cent of energy, are likely to be more appropriate than either very high or very low carbohydrate intakes," he added.

The study conclusions have received a mixed reaction from Australian health experts.

Dr Alan Barclay is a consultant dietitian and nutritionist and a Research Associate at the University of Sydney, and says it is an observational study which only shows associations, not proven causes.

"The conclusions of the paper are overstated, a major overhaul of existing dietary guidelines is not warranted based on this additional evidence," said Dr Barclay.

Professor Amanda Lee - a senior advisor at The Australian Prevention Partnership Centre - says a major limitation of the study is that it does not mention what foods the macronutrients came from.

The experienced nutritionist suggests that it's carbohydrate from added sugars and refined grains that is "problematic" and said the findings may not translate in Australia.

"The upper levels of intakes of carbohydrate reported in the study are much higher and the lower intakes of fats are very much lower than consumed here," Prof Lee explained.

However, Professor John Funder at the Hudson Institute of Medical Research says what the study shows is that fats - saturated, mono-unsaturated and polyunsaturated - are not the "no-no" most people have been brought up to believe.

"So go for dairy, olive oil and even the occasional wagyu beef burger, have lots of grains, fruit and vegetables, and lay off the sweet stuff - especially the empty calories in the 16 teaspoonfuls of trouble in sugar-sweetened soft drinks," Prof Funder said.