By Marika Sboros
Major new research, the PURE study, is creating controversy about dietary guidelines globally. It shows that the more fat you eat, including saturated fat, the lower your risk of dying from heart disease.
And the more carbohydrates you eat, the higher your risk of heart attack or stroke.
PURE (Prospective Urban Rural Epidemiology) cohort study, is the largest ever investigating links between carbs, fats, cardiovascular disease (CVD) and death. Thirty-seven researchers looked at dietary habits of 135,335 people in 18 countries over five continents with an average follow-up of 7.4 years. They are calling for changes to the guidelines. They say that the much-disputed cap on dietary saturated fat (no more than 10% of energy intake) is wrong.
Critics say PURE proves that low-fat diets are as lethal for hearts as low-carb experts claim. Others say PURE shows no need for change and doesn’t exonerate saturated fat.
PURE investigators say that the guidelines are based mainly on research in Europe and North America. Their study, published in The Lancet, is the first to investigate dietary habits in low-, middle- and high-income population groups global. Regions covered include the Middle East, Africa, China, North and South America, Europe and South Asia.
Click here to read: Swiss Re: Dietary guidelines a ‘failed human experiment’
The authors say that the guideline recommendation to restrict saturated fatty acids at below 10% of energy intake lacks evidence. It is largely based on “selective emphasis on some observational and clinical data”.
They say that this is despite evidence from several randomised trials and observational studies that “do not support these conclusions”.
They also say that the guidelines should focus on reducing carbohydrate, not fat, intake.
PURE’s lead author is epidemiologist Dr Mashid Dehghan, an investigator at Canada’s Population Health Research Institute. Dehghan is also senior research fellow at McMaster University Department of Medicine.
In media releases on McMaster’s website, Dehghan says that the guidelines are based largely on carbohydrate consumption in Europe and North America. She describes this as “moderate” at around 50% to 55% of energy intake.
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%)”. This seems to be linked to “worse health outcomes”.
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. By that, she means approximately 50-55% carbohydrates and around 35% total fat, including saturated and unsaturated.
Her PURE co-author Dr Andrew Mente is associate professor in McMasters University Department of Health Research Methods, Evidence, and Impact. Also in media press releases, he gives the finding from a related PURE study. It shows an association between a higher fruit, vegetable and legume consumption with lower mortality risk.
Data show that people will derive maximum benefit from three to four servings of fruit, veg and legumes a day, Mente says. Higher servings achieve no added benefit. This makes the three-to-four recommendation is “more affordable” for poorer countries than the current recommended five servings.
The data do not show an association between low-carbohydrate intake and health outcomes. However, the authors say this “does not provide support for very low carbohydrate diets – less than 50% energy”.
The authors note limitations, including that they based diet measures on when the study began. They also did not look at specific types of foods from which people derived nutrients.
In a linked comment in The Lancet, Dr Christopher Ramsden and Dr Anthony Domenichiello, from the US National Institute on Aging, describe the PURE study as “an impressive undertaking”. However, while it challenges the definition of a healthy diet, key questions remain, they say.
So, will dietary guideline change anytime soon? US specialist Dr Alice Lichtenstein thinks not.
Lichtenstein is a professor, senior scientist and director of Tufts University’s Cardiovascular Nutrition Laboratory. She was vice-chair of the US Department of Agriculture’s 2015 Dietary Guidelines Advisory Group. She is also primary author of the American Heart Association’s (AHA’s) Diet and Lifestyle Recommendations.
She says that “rarely are guidelines changed based on a single study”.
The basic message, whether from the 2015 DGA or AHA, is “to replace SFA (saturated fatty acid) with unsaturated fat, MUFA and PUFA (monounsaturated and polyunsaturated 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 (eg soybean oil, canola oil).
Lichenstein also says that clinical trials do, in fact, support benefits of replacing SFA (saturated fatty acid) with PUFA.
“The critical factor,” she says, ” is that the clinical data do not support replacing SFA with carbohydrate, particularly, refined carbohydrate”. Many reviews “have not taken this into consideration”.
It would be preferable to have dietary fat recommendations as an unsaturated to saturated fat ratio rather than solely on saturated or total fat, Lichtenstein says.
British obesity and public health researcher Dr Zoë Harcombe is relatively muted in PURE’s praise.
“Total mortality is always the most important measure to review,” Harcombe says. No study should claim “that X is better for condition Y” unless researchers have also assessed total mortality.
“There is no point reducing heart disease if cancer, for example, increases concomitantly,” she says. Harcombe quotes Scottish GP and CVD specialist Dr Malcolm Kendrick: “I can do an RCT (randomised controlled trial) where no one in the intervention arm will die of cardiovascular disease. The intervention shall be jumping off a cliff!”
Harcombe also makes the point about the need for caution with epidemiological studies, which can only suggest association. If researchers observe an association (in this case, the association between total fat and individual fat intake with lower mortality), this should be subjected to the Bradford Hill criteria and/or RCTs, Harcombe says.
RCTs have tested dietary fat interventions and total mortality, she says. “Even better, we now have meta-analyses of these RCTs. None – none – that bears repeating – found any significant difference in dietary fat interventions and total mortality.” Click here for a summary of RCT meta-analyses.
Click here to read: You need 5-a-day fruit, veg? No you don’t! – Harcombe
Knowing that the RCT/meta-analysis findings found nothing supports the suggestion for caution, Harcombe says. However, involvement of 18 different countries in the PURE study is an “interesting caveat”.
As the researchers note, most existing data are from European and North American populations, Harcombe notes. Thus, it may be that higher fat intake “causes” lower mortality when researchers study more diverse populations.
“But we can’t claim this yet,” she says.
Harcombe has spent many years examining the evidence base for dietary fat guidelines. She therefore wholly supports the PURE conclusion: “Global dietary guidelines should be reconsidered.”
US science journalist Nina Teicholz sees different “big news” in the PURE study.
Teicholz is author of the groundbreaking Big Fat Surprise, Why Butter, Meat and Cheese Belong in a Healthy Diet. Her book is a compelling history of just how and why nutrition science lost its way.
She also shows how ” overzealous researchers, through a combination of ego, bias, and premature institutional consensus, have allowed dangerous misrepresentations to become dietary dogma”.
Teicholz makes the point that the US dietary guidelines no longer have a formal “low-fat diet” recommendation. The US government has “talked back from this language”.
The PURE researchers say a low-fat diet is not healthy. However, they don’t endorse what she and other nutrition experts would call a “high-fat” diet. On total fats, PURE said that 30-35% was a healthy range. Teicholz says that she and others consider this a “fairly low-fat diet”. Thus, that’s not “such big news”.
Low-carb experts would also consider the recommendation of carbs at around 50-55% as high, not “moderate” as the PURE researchers describe it.
One of the most important findings of PURE is the association between low consumption of saturated fats (below 10%) and higher mortality and increased risk of stroke, Teicholz says.
“These are worrisome findings. They should spur the US guidelines to reconsider their recommendation to eat below 10% of calories as saturated fat.”
The American Heart Association especially should reconsider its advice for those with cardiovascular disease to lower their saturated fat intake to 5-6% of calories.
“The PURE findings suggest that the AHA guidelines are increasing risk for these patients,” Teicholz says.
Click here to read: Teicholz: How low-fat diets can kill you
What is also news is that the PURE results clearly do not support continued caps on saturated fats, she says. Just as critical is that clinical trial data also support this observational data.
Thus, all the data confirm that saturated fats have no effect on cardiovascular or total mortality, Teicholz says.
The limits on saturated fat are the sole reason that the guidelines recommend “lean meat” and “low-fat” milk. That makes it clear “that the science does not support these recommendations”, Teicholz says.
Therefore, those in positions of power should “retire these caps”.
Teicholz has a similar view of the PURE findings on carbohydrates. The guidelines recommend 50-55% calories, which she and many others still consider too high.
“But PURE is saying that this is the right zone,” Teicholz says.
On fruits and vegetables, the researchers found that three to four servings are enough for benefits. However, the findings also show that the benefit came from fruit but not from vegetables, Teicholz says.
Thus, PURE supports moderate consumption of fruits only and veggies “not at all”. PURE therefore clearly does not support the “plant-based” diet, she says, despite claims.
South African scientist and low-carb expert Prof Tim Noakes sees value in the PURE study. It refutes the advice that the less fat and more carbohydrate a population eats, the healthier the population will be, Noakes says.
It also shows that the majority of the populations, which the researchers studied, are indeed eating high carbohydrate diets – as a result of official dietary guidelines.
“Yet the individuals in those populations who are eating the most carbohydrate are the sickest,” Noakes says.
What the PURE data don’t reveal is what would happen if people reduced their carbohydrate intakes to below 30%.
“That’s where levels were in most humans before the agricultural revolution approximately 12,000 years ago or indeed in many European countries as recently as 100-200 years ago.
“When we ate that way, the modern chronic diseases linked to insulin resistance (heart disease, obesity, diabetes, hypertension, dementia and cancer) were largely unknown,” he says.
The PURE study should cause us to remember something vital, Noakes says. “Before the introduction of the modern diet of highly processed carbohydrates, humans were remarkably free of cancer and heart disease.”
PURE begins to show what dietary factor is most responsible for the current ill-health of so many humans.
“It is not fat,” says Noakes.