Global dietary guidelines should change to suggest people can eat more fat than previously thought, with a view to preventing overconsumption of carbohydrates, according to a new international study led by Canadian researchers.
"Our findings do not support the current recommendation to limit total fat intake to less than 30 per cent of energy," said the paper published in the Lancet on Tuesday. "Individuals with high carbohydrate intake might benefit from a reduction in carbohydrate intake and increase in the consumption of fats."
Scientists from McMaster University in Hamilton and other researchers used questionnaires to document the fat, carbohydrate and protein intake of 135,335 people in 18 countries, then followed them over an average of about seven years.
The research team, led by Mahshid Dehghan, a nutrition epidemiologist at McMaster, was set to present the results of the study at the European Society of Cardiology Congress in Barcelona on Tuesday.
The researchers looked at whether or not participants of the epidemiological study developed heart disease or stroke. They also documented the number of deaths due to cardiovascular disease as well as other causes, including cancer, and respiratory and infectious diseases.
Contrary to popular thinking over the last few decades, the researchers found no significant association between eating more than the recommended amount of fat and developing heart disease or having a stroke. In addition, a fat intake of about 35 per cent of total calories was associated with a lower overall risk of dying compared to a lower percentage of fat in the diet.
In contrast, people who ate a lot of carbohydrates (more than 60 per cent of their total calorie intake) were at higher risk of death overall, as well as death not related to cardiovascular disease.
"When you recommend lowering fat, by default, people increase their carbohydrate consumption," said Dehghan. "And increasing consumption of carbohydrates results in higher risk of mortality."
'Moderation is the solution. Don't eat too much of any single thing.'
- Richard Bazinet, U of T's Department of Nutritional Sciences
That's why nutritional guidelines around the world need to change, Dehghan told CBC News.
"Relaxing current restrictions on fat and emphasizing on carbohydrate intake ... is more likely to be beneficial."
The study did not find that a certain type of fat — saturated or unsaturated — had any significant impact on cardiovascular disease. In fact, both saturated and unsaturated fats were associated with a lower risk of total mortality and stroke.
However, the authors note that they were unable to specifically measure trans fat consumption — a potentially important limitation in the study. Cardiologists have recognized the specific danger of trans fats, which are artificial and also known as partially hydrogenated oils. Canada is moving toward banning trans fats — something New York City has already done in its restaurants and bakeries.
There has been mounting scientific evidence over the last five years challenging the long-held notion that fat is to blame for cardiovascular disease and death, said Richard Bazinet, of the Department of Nutritional Sciences at the University of Toronto, who was not involved in the Lancet-published study.
In the last couple of decades, that notion led to a slew of low-fat and fat-free products on grocery store shelves.
The problem, Bazinet said, is many of those products contain high levels of sugar and carbohydrates, substituting other sources of calories that pose health risks.
"We're seeing that play out maybe with people thinking that things like juices are fine and sweetened, you know, foods that say low in fat are a great choice. A cookie's still a cookie even if it doesn't have saturated fat or high fat content."
Dehghan, the study's lead author, emphasized that the research looked solely at cardiovascular disease and mortality, and did not look at the effects of fats and carbohydrates on obesity — a health issue of particular concern in North America.
According to Statistics Canada, more than half of adult Canadians were overweight or obese, based on body mass index (BMI), in 2014.
Although Bazinet largely agrees with the study's findings, he said the constant onslaught of research focused on specific nutrients like fat or carbohydrates and "blaming one versus the other" may be "missing the mark" in educating the public on how to make healthy food choices.
"Moderation" is the solution, he said. "Don't eat too much of any single thing."