Carb-heavy diets decried
A new study involving over 100,000 participants suggests a high fat diet is less dangerous than a high intake of carbohydrates.
Reducing total fat intake, and replacing it with a high intake of carbohydrates may be linked to worse health outcomes, according to the international study published in The Lancet.
The study – which used data on over 135,000 people from 18 countries - found that high fat diets (about 35 per cent energy – including both saturated and unsaturated fats) were associated with a lower risk of mortality, while a high intake of carbohydrates (above 60 per cent energy) was associated with a higher risk.
The study found that on average, globally, people’s diets consisted of over 60 per cent energy from carbohydrates and 24 per cent energy from fats, suggesting that rather than focusing on reducing fat intake in diets, guidelines should instead focus on reducing carbohydrate intake.
Additionally, while current guidelines recommend reducing saturated fat intake to below 10 per cent, very low intake of saturated fats (below 3 per cent) was associated with a higher risk of mortality, compared to diets with a higher intake of saturated fats of up to 13 per cent.
“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,” says lead author Dr Mahshid Dehghan, McMaster University, Canada.
“In low- and middle-income countries, where diets sometimes consist of more than 65 per cent of energy from carbohydrates, guidelines should refocus their attention towards reducing carbohydrate intake, instead of focusing on reducing fats.
“The best diets will include a balance of carbohydrates and fats – approximately 50-55 per cent carbohydrates and around 35 per cent total fat, including both saturated and unsaturated fats. Our study did not look at trans fats, typically from processed foods, and the evidence is clear that these are unhealthy.”
The study included 135335 participants aged 35-70 from 18 countries across various regions including the Middle East, South America, Africa, China, North America and Europe, and South Asia.
Each participant provided information on their socioeconomic status, lifestyle behaviours, medical history, family history of cardiovascular disease, weight, height, waist and hip measurements, and blood pressure.
They also completed a questionnaire on the types of foods and beverages they consumed, what size portion and how often, which the researchers used to calculate the amount of calories they derived from carbohydrate, fats and protein every day.
Participants’ completed follow-up visits with the research team at least every three years to record information on cardiovascular disease (i.e fatal and non-fatal heart attacks, stroke and heart failure) and death for 7.4 years.
The team analysed rates of cardiovascular events (for example, heart attack, stroke, heart failure), non-cardiovascular deaths and deaths.
During the study, 5796 people died (including 1649 from cardiovascular disease and 3809 from non-cardiovascular disease) and 4784 had a major cardiovascular disease event (2143 heart attacks and 2234 strokes)
Diets high in carbohydrates (average of 77 per cent energy from carbohydrates) were associated with a 28 per cent higher risk of death, compared with low carbohydrate diets (46 per cent energy from carbohydrates), with 7.2 deaths per 1000 people years, compared with 4.1.
Comparatively, diets with high total fat intake (35.3 per cent energy from fat) were associated with a 23 per cent lower risk of death, compared with low fat diets (11.0 per cent energy from fat), with 4.1 deaths per 1000 people years in people, compared with 6.7.
The trends were similar when looking at saturated fats, with very low intake (below 3 per cent) associated with a higher risk of mortality, compared to diets with a higher intake of saturated fats of up to 13 per cent. Similarly, diets with very low intake of mono and polyunsaturated fats (3.6 per cent and 2.2 per cent) were associated with a higher risk of mortality, compared to diets with higher intakes (13 per cent and 9.1 per cent).
“Despite there being no association between low carbohydrate intake and health outcomes, this does not provide support for very low carbohydrate diets – less than 50 per cent energy. 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.” explains Dr Dehghan.
The authors note some limitations, including that the diet measures used were based on when the study began. Additionally, the study did not look at the specific types of foods the nutrients were derived from, but the team says it will assess this in future analyses.
“It is important to put the results of the Dehghan, et al. paper in to an Australian context,” says Dr Alan Barclay - a consultant dietitian and nutritionist and a Research Associate at the University of Sydney.
“Based on our most recent national health survey, Australian’s consumed on average just over 43 per cent of energy from carbohydrate and 11.5 per cent of energy from saturated fat.
“On face value, this means that Australians should be consuming more carbohydrate and less saturated fat – consistent with our current dietary guidelines.”
Professor Jennie Brand-Miller, an expert in human nutrition at the University of Sydney, says Australians are ahead of the curve.
“We recognised that carbohydrates were not created equal over 3 decades ago – some were harmful because they increased fluctuations in blood glucose (i.e they had a high GI). Since then we have reduced our intake of added sugars and as well as high GI starches,” she said.
“Australians and the Australian food industry should be congratulated.”
Dr John Funder, a Professor in the Department of Medicine at Monash University, was impressed by the study.
“This is a good study, across a range of countries with high, mid and low average income populations,” he said.
“What it shows is that fats - saturated, mono-unsaturated, polyunsaturated - are not the no-no we have all been brought up to believe in the context of high carbohydrate diets when the source of the latter is refined sources such as sugar, rice etcetera.
“Highly significantly, lower levels of various cardiovascular morbidity and mortality were seen between diets with up to 35 per cent of calories from fat over those low in fat and high in carbohydrate.
“Complex carbohydrates - as in fruit and vegetables - are probably another thing, and not similarly a problem.
“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.”