June 15, 2017
The American Heart Association (AHA) has issued a new "Presidential Advisory" on dietary fats and cardiovascular disease to "set the record straight" on the harms of saturated fats.
The statement, published online in Circulation on June 15, continues to strongly recommend replacing saturated fats with poly- and monounsaturated vegetable oil to help prevent heart disease.
The statement also recommends that the shift from saturated to unsaturated fats should occur simultaneously in an overall healthful dietary pattern, such as DASH (Dietary Approaches to Stop Hypertension) or the Mediterranean diet, and that "good carbohydrates," such as whole grains and whole fruits, are other appropriate foods to substitute for saturated fats.
"We want to set the record straight on why well-conducted scientific research overwhelmingly supports limiting saturated fat in the diet," lead author, Frank Sacks, MD, professor of cardiovascular disease prevention at the Harvard T.H. Chan School of Public Health, Boston, Massachusetts, said in a statement from the AHA.
Outside nutritional experts contacted by Medscape Medical News for comment were fully supportive of the advisory, describing it as "an outstanding paper," "exacting in its review of the evidence," and "full of common sense."
"The AHA leadership decided that they needed to put out a new advisory on diet — particularly fats — because of various commentators on nutrition suggesting that saturated fat was innocuous, which has been widely covered in the media, but these comments were not scientifically based," Dr Sacks told Medscape Medical News.
The issue in nutrition research, he said, is that a great deal of attention has been paid to new studies that may not be scientifically rigorous but have controversial results.
"There has been a growing trend of media articles focusing on small studies suggesting some saturated fats are good for you," Dr Sacks said. "People advocating that eating butter and full-fat milk is beneficial. And coconut oil is a fad right now — but it is actually a saturated fat, which raises your LDL [low-density lipoprotein], so the AHA wanted to look at the issue again."
It is called a Presidential Advisory, he said, since the AHA president identified it as a key issue that needed attention.
"This advisory is based on careful scientific review — it has been organized in a very systematic way, involving experts from a wide range of fields who have looked very carefully at the literature," he said. "Then the recommendations have been thoroughly vetted and questioned through multiple levels of peer review and scientific advisory committees across the entire AHA."
Dr Sacks explained: "This statement focuses on fats — what fats should we be eating — and we come down very strongly that we should eat less saturated fats, and these can be replaced by polyunsaturated and monounsaturated fats."
The statement notes that scientific studies that lowered intake of saturated fat and replaced it with polyunsaturated vegetable oil reduced cardiovascular disease by approximately 30%. In addition, several studies found that coconut oil — which is predominantly saturated fat but widely touted as healthy — raised LDL cholesterol the same way as did other saturated fats found in butter, meat, and palm oil.
"We really wanted a document suitable for both healthcare professionals and the public which is not full of jargon and scientific language," Dr Sacks said.
"Our message is that polyunsaturated fats are the best fats to eat. They are found mainly in vegetable oils such as soy bean oil, peanut oil, corn oil," he said. "Monounsaturated fats, found in sunflower oil, olive oil, nuts, and avocado, are also okay — much better than saturated fats, but not as healthy as polyunsaturated fats."
The last few years has seen an increase in knowledge on benefits of polyunsaturated fats, he said. "They are associated with a reduction in total mortality and no compensatory increase in death from other causes; they are also associated with a reduction in insulin resistance. The same is seen with monounsaturated fats, but the effect is less."
Good vs Bad Carbs
The statement also addresses the issue of substituting carbohydrates for saturated fat and reports that replacement of saturated fat with mostly refined carbohydrates and sugars is not associated with lower rates of cardiovascular disease. However, evidence from prospective observational studies indicates that carbohydrates from whole grains and whole fruits are associated with reduced heart disease when they replace saturated fat.
"It is no good eating less saturated fat if you are going to substitute it with white bread, sugar, and processed carbohydrate," Dr Sacks elaborated. "But there have been studies in the last few years which have been able to separate out carbohydrates, and these have shown that, rather like fats, there are good carbs and bad carbs."
He says the message has got muddled. "People have been eating bad carbs instead of saturated fat. This will not reduce your risks of heart disease. We wanted to spell it out that there are different types of carbohydrates and people should be eating the good ones. If people replace saturated fats with these good carbs, then there is a reduction in coronary heart disease."
He concluded: "There is nothing particularly revolutionary in this statement — the evidence base has been stable and has always recommended reducing saturated fats and increasing polyunsaturated fats. The latest studies reinforce that view. But we have learnt more about carbohydrate in the last few years."
Experts in nutrition contacted by Medscape Medical News all welcomed the new advisory, saying they thought it contained robust recommendations and was well timed.
"There has been concern about various unqualified individuals — self-proclaimed experts who are promoting a new book or suchlike — touting the idea that saturated fat is good for you, which has attracted a lot of media attention," said David Jenkins, MD, Departments of Nutritional Sciences and Medicine, University of Toronto, Ontario, Canada, who was not a part of the advisory writing group.
"But the AHA has always taken the stance that saturated fat is bad and that we should be eating more plant oils, and this view is endorsed by the vast majority of nutritionists who are scientifically qualified," he told Medscape Medical News.
"It is very important that they have issued this statement," he added. "The AHA president called for this to be done because things were getting out of hand. The AHA is restating the obvious. The message is consistent with what we have always believed. It has been preserved through stormy waters because it was right in the beginning."
Professor Jenkins noted that the problem with nutrition is that "nothing is absolute. A bad diet will kill one person but not another one. There are always examples of people who lived until they were 100 and ate a diet high in saturated fat. But you can also find the same with people who smoke very heavily; they just have good genes. But when all the evidence is reviewed carefully as has been done with this advisory, then you can find what is really going on."
The document, he adds, is "full of common sense. It is not controversial. It has tried to keep away from the 'meat versus vegetables' debate, which will get them into trouble with the farmers, but 'saturated fat' is scientific code for 'animal fat.' This statement is telling us to eat less meat, but they are not actually using those words. There is now a weight of evidence that plant foods — which are very low in saturated fat — are beneficial. It has been shown time and time again that these foods can reduce heart disease."
'Evidence-Based Reality Check'
David Katz, MD, director of the Yale University Prevention Research Center, and founder and president of the True Health Initiative, described the new AHA advisory as "one of the most important papers addressing the topic of saturated fat and health outcomes."
"The paper is outstanding because it is methodical, comprehensive, and exacting. All of the areas of alleged controversy (pseudo-controversy in fact) regarding saturated fat and health are addressed," he said. "Evidence is viewed both expansively and systematically, and the paper nicely differentiates decisive answers from unresolved questions. There is also an appropriately complete view of evidence — drawing information from the alignment of mechanistic studies, human intervention studies, and observational epidemiology. Statistical robustness is appended with formal meta-analysis.
"The conclusion is perfectly clear and entirely decisive: Saturated fat from the usual dietary sources increases the risk of heart disease, and its replacement with wholesome foods and unsaturated fats reduces that risk."
Dr Katz said the paper was well timed. "It is clearly responsive to the many high-profile and misguided efforts to discredit the well-substantiated links between saturated fat in the diet and blood lipids and between blood lipids and cardiovascular disease. Misrepresentations in these areas have real potential to cost lives, so this paper is an urgently needed, well-timed, and impressively evidence-based reality check."
Deirdre Tobias, MD, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, who recently published a meta-analysis of studies suggesting that low-fat diets are not particularly effective in helping people lose weight over the long term, was also impressed with this new AHA statement.
"The science against saturated fats may not have changed much over the past few decades, but we have come to realize that the way in which science is translated for public health messaging can have a huge impact," she told Medscape Medical News.
The AHA has long advocated a diet low in saturated fat, Dr Tobias noted. "However, key to this Presidential Advisory statement is the language of replacement, which emphasizes swapping saturated fats out for polyunsaturated fats. Further, they put this in the context of an overall healthy dietary pattern, rather than just focusing on a single nutrient."
"For several decades, saturated fats have been the target of 'lower is better' (eg, <10% of calories from saturated fat), often with little advice as to what should be replacing this source of calories," she added. "Recent large studies have clearly demonstrated that replacing saturated fats with refined carbs and sugars does nothing to lower CVD [cardiovascular disease] risk, while replacing with healthy fats can substantially lower risk.
"With this statement, it is clear that the AHA recognizes the need to specify these important substitutions for the sake of public health, and to better inform its clinicians and patients."
Dr Sacks has disclosed no relevant financial relationships. Disclosures for coauthors appear in the publication.