Low-fat diets could increase your risk of dying early, according to a large study that adds to confusion over healthy eating advice.

Those who ate the least fats were a quarter more likely to die during the study, suggesting that what people eat instead of meat and dairy products could be even more dangerous.

Those who ate the most carbohydrates were 28 per cent more likely to die during the study. The Canadian researchers called for global dietary guidelines to be revised to warn against white bread and rice.

For years healthy eating advice has centred on urging people to cut down on fatty food, particularly saturated fats from animal products. Recently some researchers have started to question the evidence for this, arguing that carbohydrates are the bigger threat. Efforts to warn people off butter could be counterproductive if they eat more white bread and sugar instead, experts have said.

“When you emphasise lower fat people replace fat with carbohydrate and the harm of refined carbohydrates has been shown by our research,” said Mahshid Dehghan of McMaster University in Ontario, who led the study of 135,000 people in 18 countries over a decade.

She said her findings suggested that the average British diet was actually pretty healthy. “We are suggesting moderation. We see in Europe and North America people consuming around 50 to 55 per cent energy from carbohydrate and about 30 to 35 per cent fat. Our data shows that at this level there is no harm.”

The average Briton gets about 35 per cent of their calories from fat, the same amount as the average for the top 20 per cent of fat eaters in Dr Dehghan’s study. She found that 4.1 in 1,000 of them died, compared with 6.7 in 1,000 of the people with the lowest fat intake — those who got an average of 11 per cent of their calories from fat.

There were 7.2 deaths per 1,000 people each year among the group that ate the most carbohydrate, averaging 75 per cent of calories. This compared to 4.1 in the group that ate the least, averaging 46 per cent of calories, similar to the British average.

Dr Dehghan told the European Society of Cardiology congress in Barcelona that her findings “add to the large and growing body of evidence that increased fats are not associated with higher cardiovascular disease”.

Although her study did not look at why fat was protective, she said: “The body needs fat. It carries vitamins, it provides essential acids, it has a role in the body. When you reduce fat to very low levels, you’re affecting these important minerals. Maybe the reason is we’re losing vitamins.”

Professor Susan Jebb, a professor of diet from Oxford University, said the findings were “a thumbs-up for UK recommendations which advise up to 35 per cent energy from fat and 50 per cent energy from carbohydrate, of which only 5 per cent should be sugar”.

Professor Jeremy Pearson of the British Heart Foundation said: “This study suggests that we should perhaps pay more attention to the amount of carbohydrate in our diet than we have in the past and we may need to revise the guidelines. What I don’t think people should do is get excited and think ‘I can eat as much saturated fat as I like’.”

However, Christopher Ramsden, of the US National Institutes of Health, said that the findings “add to the uncertainty about what constitutes a healthy diet” and raised the possibility that meat and dairy products actually lengthen life. Writing in The Lancet, he said: “This uncertainty is likely to prevail until well designed randomised controlled trials are done. Until then, the best medicine for the nutrition field is a healthy dose of humility.”

Aseem Malhotra, a cardiologist who has been critical of current guidance, said: “Let’s make starchy refined carbohydrates an occasional treat, not a staple. Restricting refined carbohydrates should be the priority for living longer. The science is now telling us that poor dietary advice has been the biggest contributor to poor health.”

Alison Tedstone, chief nutritionist at Public Health England, said: “High-fat diets can also be high in calories and can lead to weight gain, while too much saturated fat is associated with increased blood cholesterol. Both of these are associated with increased risk of heart disease.”