Why do health authorities advise us to restrict our saturated fat intake?
The belief that saturated fat is unhealthy has been widely held since the 1960s. For decades, we've repeatedly heard terms like "artery-clogging saturated fat" and as of 2018, the message hasn't really changed among mainstream health authorities and their leading spokespeople.
When discussing new recommendations to restrict saturated fat to less than 10% of daily calories in early 2018, Director of the WHO's Department of Nutrition and Health Development Francesco Branco stated:
"Dietary saturated fatty acids and trans-fatty acids are of particular concern because high levels of intake are correlated with increased risk of cardiovascular diseases."
Recently, a Harvard professor characterized coconut oil as " pure poison " due to its high saturated fat content.
The fear of saturated fat can be traced back to the diet-heart hypothesis first proposed in the 1950s by American scientist Ancel Keys who promoted his theory that dietary fat raises cholesterol levels, thereby increasing the risk of heart disease.
The diet-heart hypothesis: incriminating saturated fat with weak evidence
After traveling to Europe and conducting informal surveys in different populations there between 1951 and1952, Keys published a paper suggesting that as a country's intake of fat, saturated fat, and cholesterol increased, its rates of coronary heart disease (CHD) and related deaths likewise increased.
Importantly, this was based entirely on observational data, which is considered weak evidence unless correlations are strong and have been repeatedly duplicated in other studies. Even then, this type of research can only show that a behavior and an outcome are associated with an outcome but not that the behavior actually caused the outcome.
That, however, wasn't the only problem with Keys' research.
In another 1953 paper, he included a graph showing a strong association between fat intake and CHD mortality in residents of six countries.However, in 1957, researchers Yerushalamy and Hilleboe published data from 22 countries that failed to show a significant relationship between the amount of fat these populations consumed and their rates of CHD mortality.
Decades later in the late 1980s, Keys and his research team published the results of their "Seven Countries Study" that tracked diet, health and death data in residents of the US, Japan, and Europe over 25 years. In this paper, Keys stated that although total fat and cholesterol intake weren't associated with death from CHD, saturated fat intake was. He concluded that populations that ate little saturated fat had low rates of CHD mortality, whereas those with higher saturated fat intake (like the US) were at increased risk for CHD and CHD-related death. Yet he cherry-picked his findings: data from countries where people consumed high amounts of saturated fat but had low rates of CHD mortality - such as France and Switzerland - weren't included in the Seven Countries Study.
These results would end up influencing nutrition policy for decades to come.
In 1961, based on Keys' ongoing research and other papers favorable to the diet-heart hypothesis, the American Heart Association endorsed low-fat diets for the prevention of heart disease. Sixteen years later, a diet low in total and saturated fats was incorporated into the first set of US dietary guidelines.
Other problems with saturated fat research
Although Keys acknowledged that his findings were based on observational evidence, he strongly believed that his findings proved the diet-heart hypothesis to be true. However, a controlled clinical trial is the only way a cause-and-effect relationship can be proved. But when the National Institute of Health began conducting clinical trials on saturated fat, there were other issues - some of which weren't revealed until several years later.
Results from controlled trials that failed to find any relationship between saturated fat and risk of CHD mortality or death from other causes often weren't published within a reasonable time frame. In the Minnesota Coronary Experiment, conducted from1968 to1973, more than 9,500 people participated in a randomized study that looked at the effect of replacing saturated fat with linoleic acid (an omega-6 polyunsaturated fat found in vegetable and seed oils). This study has been described as the largest, most rigorous controlled study of its kind to date.
No benefit was found in the linoleic acid group; however, these results weren't published until 1989.The Minnesota Coronary Survey In 2016, an analysis of additional, previously unpublished data from the Minnesota Coronary Experiment confirmed the lack of association between saturated fat and CHD, heart attacks, and risk of death. Moreover, although the linoleic acid group experienced a decrease in LDL cholesterol levels, these participants actually had a slightly higher risk of CHD mortality. The 2016 researchers stated this was likely due to adverse metabolic changes resulting from intake of linoleic acid, which is known to be inflammatory when consumed in high amounts.
Similarly, in 2013 an analysis of uncovered data from the Sydney Diet Heart Study conducted between 1966 and 1973 found that replacing saturated fat with linoleic acid slightly increased the risk of death from CHD and other causes.
Saturated fat and health risks: the evidence to date
A few years ago, we shared some interesting WHO statistics that revealed that people living in European countries with the highest consumption of saturated fat have the lowest risk of dying from heart disease.
And what do systematic reviews of observational studies and controlled studies - considered the strongest, most reliable evidence - tell us about saturated fat intake and the risk of CHD, other diseases, and death from any cause?
- A 2009 meta-analysis of 28 cohort studies and 16 randomized controlled trials (RCTs) found no significant association between saturated fat intake and CHD events or CHD mortality.
- A 2010 meta-analysis of 21 cohort studies found no association between saturated fat intake on CHD outcomes aside from a slightly lower risk of stroke.
- A 2015 meta-analysis of 17 observational studies found that saturated fats had no association with heart disease, all-cause mortality, or any other disease.
- A 2017 meta-analysis of 7 cohort studies found no significant association between saturated fat intake and CHD death.
And although two systematic reviews of clinical trials found that replacing saturated fats with unsaturated fats may slightly reduce the risk of heart attack and other cardiovascular events, many other extensive reviews have failed to establish any such benefit.
Recently, Mente and colleagues published a large study that examined dietary patterns and lipid data from over 100,000 people in 18 countries around the world. Called the PURE study, its data analysis found that higher saturated fat intake was associated with beneficial effects on a number of cardiovascular risk factors, including higher HDL levels, lower triglyceride levels, and - what seemed to be the strongest predictor of CHD risk - a decreased ratio of ApoB (found in LDL particles) to Apo A (found in HDL particles)
What's more, although eating a lot of saturated fat was linked to higher LDL cholesterol levels, these elevated values didn't reliably predict future heart attack events or deaths. Therefore, lowering saturated fat intake in an effort to reduce LDL cholesterol isn't likely to decrease the risk of cardiovascular events. Additional follow up seven years later in the PURE study revealed no association between saturated fat intake and heart disease but in fact a decreased risk for all-cause mortality and stroke.
It appears that high saturated fat intake may increase LDL cholesterol concentrations in some people, either modestly or significantly. Additionally, researchers report that myristic acid (a saturated fat found in many foods like coconut oil, palm kernel oil, butter, cream, cheese and meat) has a greater effect on both LDL and HDL cholesterol levels than most other saturated fats.
Should saturated fat ever be restricted?
Despite strong evidence that saturated fat itself is not harmful, in some instances limiting it might be beneficial. For instance, results from a recent study suggest that in patients with cardiovascular disease, eating a lot of saturated fat might lead to higher concentrations of small and medium LDL particles - changes that could promote disease progression. However, response to high saturated fat intake may vary among people with CHD. An earlier study found a beneficial increase in LDL particle size and other improvements in patients with cardiovascular disease who followed a high-saturated-fat, starch-free diet.
Importantly, experts in the field of lipidology and cardiology disagree about whether elevated LDL cholesterol and particle concentrations increase the risk of CHD when other biomarkers related to heart health, such as inflammation, are within normal limits.
Should you be worried about saturated fat?
In a word - no. Saturated fat is part of our evolutionary history. Many low-carb whole foods that provide valuable nutrients and satiety - such as meat and full-fat dairy products - are also rich in saturated fat. Avoiding these foods may very well do more harm than good.
Aiming for a saturated intake below 10% of calories, as most health authorities recommend, is a difficult task that requires detailed tracking of macronutrients, doesn't encourage eating naturally, and can diminish pleasure at mealtimes. Limiting fat can also decrease meal satiety and increase hunger and cravings between meals.
Additionally, coconut oil, butter, lard and other saturated fat sources are much more stable for cooking at high temperatures than unsaturated fats like olive oil and vegetable oils.
Based on the large body of high-quality research available, saturated fat intake per se is not linked to greater risk of heart disease, other diseases, or early death from any cause.
What's more, saturated fat research has typically been conducted in people following all types of diets. There is emerging evidence that consuming a lot of fat on a carbohydrate-restricted diet may be even less of a concern and could lead to overall reductions in cardiovascular risk.
On the other hand, the relationship between saturated fat intake and elevated LDL cholesterol and particle levels seems to vary from person to person. If your own LDL values increase significantly after adopting a keto or low-carb diet, you may be able to help lower them by cutting back a bit on saturated fat and eating more nuts, olive oil, avocados and fatty fish. By all means, avoid vegetable and seed oils, which are high in linoleic acid.
Conclusion
An across-the-board recommendation to limit your consumption of saturated fat to a small percentage of daily calories simply isn't based on sound scientific evidence.
Additional resources
Videos
Dietary fat & cardiovascular disease The demonization and deception in research on saturated fat, cholesterol and heart diseaseArticles
The Seven Countries Study, Part 1Most viewed BMJ paper 2017: Saturated fat does not clog the arteries
/ Franziska Spritzler, RD
