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A Meta-Analysis Finds No Link Between Consuming Saturated Fats and Risk for Heart Disease

Updated: Oct 23

How Changes in What Science Knows Confuse Us

For decades, leading health organizations warned us that eating foods high in saturated fats and cholesterol, like eggs and butter, will clog the arteries that surround our heart muscles (the coronary arteries) and give us heart attacks and other types of cardiovascular disease. This all stems from the work of an American physiologist, Ancel Keys, who launched the Seven Countries Study in 1958. That study seemed to show that high fat diets increase the risk for cardiovascular disease and, although through the years there were hints that the findings were not that robust, influenced experts around the world to issue what sounded like definitive advice: cut down on the amount of saturated fat in your diet or risk having a heart attack.


Now, a paper has been published in the European Journal of Preventative Cardiology that looked at multiple different types of studies, including randomized clinical trials, that address the relationship between diets high in saturated fat and heart disease. The authors conclude that there is in fact no evidence that diets high in saturated fat increase our risk for heart disease or that lowering one’s saturated fat intake will reduce the risk for cardiovascular disease. “Based on scientific the evidence,” the study authors conclude, “there is no scientific ground to demonize [saturated fats] as a cause of [cardiovascular disease]”


That advice to shun saturated fats in our diets is believed to have had serious adverse consequences. Foods that are low in fat are less palatable and to deal with that effect people typically consume foods with more carbohydrates, including sugar. This seems to have been an important factor in the striking global increase in obesity. Today, obesity is the second leading cause of preventable premature death in the United States, responsible for about 300,000 deaths annually. Overweight and obesity are clearly associated with increased risk for cardiovascular disease, some cancers, diabetes, and a host of other adverse health conditions. Thus, the advice to cut down on eating eggs, butter, and other foods high in saturated fats may inadvertently have fueled an obesity epidemic that is deadly.


Changing Guidelines Confuses People


In recent years, healthcare guidelines have proliferated, telling doctors when to screen for certain diseases, what tests to obtain from patients, and how to treat many conditions. Guidelines also advise the public on many health issues, including what to eat. But dietary guidelines seem to change so often that it is no surprise that people are confused and ignore them. Uncertainty about the scientific validity of diet and nutrition guidelines may be part of the reason that people are so willing to believe alternative voices who promote things like vitamin, mineral, and other supplements. Today, the supplement business is a multi-billion-dollar industry, but studies consistently show that almost no one actually needs to take them. Except for people with proven nutrient deficiencies--relatively rare in high-income countries like the U.S.--vitamins and mineral supplements are largely unnecessary. At best they are a waste of money, but in some instances they can even be harmful.


In his 2019 op-ed piece “Are Eggs Good or Bad for You?” in The Hill, Dr. David Seres, Professor of Medicine and Director of the Institute of Human Nutrition at Columbia University, bemoaned the effect that changing nutrition guidelines have on public perception. He wrote, “Nearly everyone I ask is sick and tired of how often we nutrition experts seem to change our minds about whether eggs are good or bad for you.” Seres points out that most guidelines concerning what we should or shouldn’t eat are based on observational studies. These are studies in which investigators observe the effects of a risk factor, an aspect of lifestyle, a treatment, or other interventions without making any attempt to intervene or control anything. While sometimes observational studies can yield powerful conclusions—they are how we know that cigarette smoking causes lung cancer—observational studies are prone to confounding by unmeasured variables and therefore are generally felt inferior to randomized controlled trials (RCTs) in making cause and effect conclusions. But it is very difficult to conduct RCTs for nutritional guidance because it takes many years to realize the effects of dietary choices and because it is very hard to get people to stick with specific diets for any length of time. Hence, the science underlying nutritional recommendations is often uncertain and subject to change. When it comes to nutritional guidance, Seres notes that “The reputation of science, to which I highly identify, is under attack because of our inability to make durable recommendations.”


Some Diet Recommendations Seem Secure


This makes it hard for anyone to recognize when nutritional science has reached firm conclusions that we should consider incorporating into our own diets. For example, there is now solid evidence and consensus among experts that plant-based diets are particularly healthy for most adults and reduce the risk for obesity, heart disease, some cancers, and diabetes. It is also now widely accepted that ultra-processed foods are unhealthy and increase the risk for adverse health outcomes like obesity. Right now, recommendations to increase the amount of plant-based food and decrease the amount of ultra-processed food in our diets represent the best evidence we have. The problem is whether our frustration with the many changes in nutritional guidelines will make us resistant to accept these evidence-based guidelines. It is, after all, easier to fall into the trap of believing an advertisement that taking a supplement will somehow make us healthier, a usually unfounded claim, than to follow what may seem a complicated set of recommendations to overhaul our diets.


We need to develop much better ways of communicating scientific uncertainty, the limitations of observational studies, and the ways that people can make use of health guidelines. Right now, most of what we learn about health recommendations comes from journalists’ stories about the latest findings, often taken out of context and without the necessary cautions, or from the internet, where we are as likely to encounter misinformation as we are reliable information. It is true that the scientific community hung onto the “eating saturated fat causes heart disease” and “eggs are bad for you” tropes for much too long, even as evidence was mounting that neither of those is strictly speaking true. That must not lead us to ignore recommendations when they are backed by good evidence and solid expert consensus. Although science will evolve and these recommendations may change, for now we can say that eggs are not bad for you, but highly processed foods are. All of us, and our policymakers, should act accordingly.

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