It turns out a low-fat diet should not be what the doctor ordered
PURE research shows carbohydrates increase the risk of an early death
Doctors have been telling patients for decades to eat a low-fat diet to protect them from a heart attack or stroke. Now, major new international research shows that a low-fat diet is more likely to kill people.
The PURE study, recently published in the prestigious British medical journal The Lancet, shows a low-fat diet significantly raises the risk of death from a heart attack or stroke.
According to the findings, the more fat people eat — including saturated fat — the less likely they are to die from heart attack or stroke. Data also show that the more carbohydrates they eat, the higher their risk of premature death, though not from cardiovascular disease.
PURE is the Prospective Urban Rural Epidemiology cohort study. It is the largest study investigating links between carbohydrates, fats, cardiovascular disease and death. The Canadian-led researchers presented the findings at the recent Congress of the European Society of Cardiologists in Barcelona, Spain.
Among the 37 PURE researchers from around the world is one South African: Prof Edelweiss Wentzel-Viljoen, professor of nutrition at North-West University Centre of Excellence for Nutrition and a freelance nutrition and dietetic consultant.
The findings are causing controversy in medical and dietetic circles as they contradict elements of the influential US dietary guidelines that many countries including SA, closely follow. For decades, doctors and dietitians have dished out advice based on these guidelines.
The researchers are calling for changes to official dietary guidelines. They say that the guidelines are based mainly on research in North America and Europe dating back four decades. Their study is the first to investigate dietary habits in low-, middle- and high-income population groups globally. Regions covered include the Middle East, Africa, China, North and South America, Europe and South Asia.
The researchers acknowledge the study’s limitations. PURE is observational and thus can only show association, not causation. But the authors say that other observational studies and clinical trial data over the past two decades support their findings. Data include findings from randomised controlled trials, the gold standard of medical research.
Government experts have revised the dietary guidelines in recent years. SA follows the US example and no longer has a formal low-fat recommendation. However, the guidelines recommend limiting total fat intake to less than 30% of energy and saturated fat intake to less than 10% of energy, which many nutrition experts say is still a low-fat diet.
The PURE findings do not support those recommendations on fat intake, says Canadian author Dr Mahshid Dehghan, of the Population Health Research Institute at McMaster University.
When viewed in the context of most previous studies, PURE questions conventional beliefs about dietary fats and clinical outcomes, Dehghan says.
Dietary guidelines have focused for decades on reducing total fat based on the idea that reducing saturated fat should reduce the risk of cardiovascular disease. However, this did not take into account how saturated fat is replaced in the diet.
PURE shows that when people eat less fat, they automatically increase their carbohydrate consumption, Dehghan says. “Our findings may explain why certain populations such as South Asians, who do not consume much fat but consume a lot of carbohydrates, have higher mortality [death] rates.”
The current focus on low-fat diets “ignores the fact that most people’s diets in low- and middle-income countries are very high in carbohydrates (upwards of 65%)”, she adds.
A second PURE paper takes aim at another official dietary recommendation — to eat fivea-day fruit and vegetable servings. The researchers assessed fruit, vegetable and legume consumption related to deaths, heart disease and strokes. Their findings show that three to four servings are sufficient.
Given that fruits and vegetables are relatively expensive in most middle-income and lowincome countries, the five-a-day recommendation is unaffordable for most people in many regions, such as South Asia, China, Southeast Asia and Africa, says author Victoria Miller, a McMaster doctoral student.
And while the PURE study calls for reduced carbohydrate intake, the researchers make it clear they are not supporting a low-carbohydrate intake.
Dehghan says that the guidelines are based largely on carbohydrate consumption in Europe and North America.
She describes this as “moderate” at about 50% to 55% of energy intake.
Guidelines should refocus their attention on reducing carbohydrate intake where it is high and not on reducing fats, Dehghan says.
The best diets will include “a balance of carbohydrates and fats”, Dehghan says.
She means approximately 50%-55% carbohydrates and about 35% total fat, including saturated and unsaturated.
An earlier PURE paper in the New England Journal of Medicine in 2014 questioned low-sodium (salt) dietary guidelines. The authors said that the alternative approach of recommending high-quality diets rich in potassium might achieve “greater health benefits, including blood-pressure reduction, than aggressive sodium reduction alone”.
In a commentary article in The Lancet, Dr Christopher Ramsden and Dr Anthony Domenichiello, from the US National Institute on Ageing, say that the PURE study is “an impressive undertaking”.
However, while the study challenges the definition of a healthy diet, they say that “key questions remain”.
Those responsible for dietary guidelines and nutrition advice from heart foundations have indicated that they will be making no changes.
US specialist Dr Alice Lichtenstein believes that’s wise at this stage.
A professor and director of Tufts University’s Cardiovascular Nutrition Laboratory, she was the vice-chairwoman of the US department of agriculture’s 2015 dietary guidelines advisory group. She is also primary author of the American Heart Association’s Diet and Lifestyle Recommendations.
“Rarely are guidelines changed based on a single study,” Lichtenstein says.
And clinical trials do support benefits of replacing saturated fatty acid with polyunsaturated fatty acids, she says. The basic message is to replace saturated fatty acid with unsaturated fat, polyunsaturated fatty acids and monounsaturated fatty acids, Lichtenstein says.
The recommendation to choose low- and non-fat dairy products and lean meat “seems reasonable”, she says. That’s as long as it goes with a recommendation to replace animal fats with vegetable fats. “The critical factor,” says Lichtenstein, “is that the clinical data do not support replacing saturated fatty acid with carbohydrate, particularly refined carbohydrate”.
It is also preferable to have dietary fat recommendations as an unsaturated to saturated fat ratio rather than solely on saturated or total fat, she says.
Johannesburg cardiologist Dr Riaz Motara says that the last 30 years of research has shown that chronic low-grade inflammation underpins all chronic lifestyle illnesses, including heart disease. Among the main nutritional reasons for higher inflammation levels are that people are eating far too much refined sugar and starch.
People are also eating too much omega 6-rich (grain-fed) animal protein. “Omega 6 is a pro-inflammatory fat. High omega 6-rich diets are shown to increase the risk of developing all the chronic lifestyle illnesses” Motara says.
People are also consuming micro-nutrient deficient fruit and vegetables. This is largely because almost all fruit is picked green, kept in cold storage, radiated and artificially ripened, Motara says. So, although we are eating a healthier diet, we are “starving in the place of plenty”.
“PURE confirms that we should be eating a largely greenbased diet with a higher fat (omega 3) and moderate protein (grass-fed/omega 3) and lowrefined sugar diet,” Motara says.
PURE SHOWS THAT WHEN PEOPLE EAT LESS FAT THEY ... INCREASE THEIR CARBOHYDRATE CONSUMPTION WHILE STUDY CHALLENGES THE DEFINITION OF A HEALTHY DIET, KEY QUESTIONS REMAIN