Low-fat diets could raise the risk of early death by almost one quarter, a major study has found.
The Lancet study of 135,000 adults found those who cut back on fats had far shorter lives than those enjoying plenty of butter, cheese and meats.
Researchers said the study was at odds with repeated health advice to cut down on fats.
Those doing so tended to eat far too much stodgy food like bread, pasta and rice, the experts said, while missing out on vital nutrients.
Participants eating the highest levels of carbohydrates – particularly refined sugars found in fizzy drinks and processed meals – faced a 28 per cent higher risk of early death.
The NHS cautions against having too much saturated fat, on the grounds it raises cholesterol levels, increasing the risk of heart disease.
But the latest research, presented at the European Society of Cardiology Congress, in Barcelona found those with low intake of saturated fat raised chances of early death by 13 per cent compared to those eating plenty.
And consuming high levels of all fats cut mortality by up to 23 per cent.
The Canadian study tracked eating patterns and death rates across 18 countries.
Researcher Dr Andrew Mente, from McMaster University, said: “Our data suggests that low fat diets put populations at increased risk for cardiovascular disease.
“Loosening the restriction on total fat and saturated fat and imposing limits on carbohydrates when high to reduce intake to moderate levels would be optimal.”
He said getting the balance of fats and carbohydrates right was about achieving a “sweet spot” which was best for health - meaning around 35 per cent of calories should come from fats.
Although this is in line with NHS guidance, health officials still warn Brits to cut down on their saturated fat consumption to protect their heart.
Guidance states men should eat no more than 30g daily and women 20g.
Saturated fat is typically found in animal products such as butter, cheese and red meat.
And last year Public Health England suggested increasing the proportion of starchy carbohydrates in the diet.
Lead researcher Dr Mahshid Dehghan, said: "A high carbohydrate diet - greater than 60 per cent of energy - is associated with higher risk of mortality.
“Higher intake of fats, including saturated fats, are associated with lower risk of mortality.”
But diet had little impact on heart death risk, suggesting it had a greater impact on other killers such as cancer, dementia, and respiratory disease.
Consultant cardiologist Dr Aseem Malhotra said it was time “for a complete U-turn” in Britain’s approach to diet, and demonisation of fat.
“The sooner we do that the sooner we reverse the epidemic in obesity and diabetes and the sooner start improving health.”