For decades, saturated fat has been believed to be harmful.
This is claimed to be because saturated fat raises blood levels of cholesterol inside LDL lipoproteins, which is a risk factor for cardiovascular disease (heart disease and strokes).
This is often referred to as the diet-heart hypothesis.
A new study recently came out that looks at the relationship between saturated fatconsumption and the risk of cardiovascular disease.
Hooper Lee, et al. Reduction in saturated fat intake for cardiovascular disease.The Cochrane Database of Systematic Reviews, 2015.
This is a systematic review and meta-analysis performed by the Cochrane collaboration, an independent organization of scientists that do objective and highly thorough reviews of randomized controlled trials.
When it comes to the quality of scientific evidence, it really doesn’t get much better than a Cochrane review.
Materials and Methods
The researchers searched the literature for randomized controlled trials that fulfilled certain criteria.
These included, but were not limited to:
- There was a control group in each study.
- The study instructed participants to reduce saturated fat, or replace it with other types of fats.
- The study lasted for at least 24 months.
- The study looked at hard end points, such as heart attacks and death.
All in all, 15 randomized controlled trials with over 59,000 participants were included.
There were several interesting findings in the study.
A cardiovascular event can refer to several different things. The study defined a “cardiovascular event” as:
“Combined CVD events. These included data available on any of the following: cardiovascular deaths, cardiovascular morbidity (non-fatal myocardial infarction, angina, stroke, heart failure, peripheral vascular events, atrial fibrillation) and unplanned cardiovascular interventions (coronary artery bypass surgery or angioplasty).”
In the current review, intervention that reduced saturated fat intake led to a 17% reduction in cardiovascular events. The quality of evidence was deemed “moderate.”
All-cause mortality refers to death from any cause, including heart attacks, cancer, accidents and others.
This study showed that reducing saturated fat has no statistically significant effect on total mortality. In other words, you are just as likely to die if you significantly cut back on saturated fat intake.
Cardiovascular mortality implies death caused by either heart attacks or strokes. These are currently the two of the world’s most common causes of premature death.
This study did not find any benefit of reducing saturated fat. In other words, those who reduced their intake of saturated fat were just as likely to die from heart attacks or strokes.
Fatal heart attacks
The study almost found a small reduction in fatal heart attack risk by reducing saturated fat. The risk ratio was 0.95, or a 5% reduction in risk.
However, this was not statistically significant.
Non-fatal heart attacks
The study found no reduction in non-fatal heart attacks.
There were no reductions in strokes (bleeding or a blood clot in the brain) in groups who restricted their saturated fat intake.
All in all, the only benefit of reducing saturated fat intake was found in cardiovascular events. There was no statistically significant effect on mortality, death from cardiovascular disease, heart attacks or strokes.
However, when they analyzed the studies further, they found a significant reduction in cardiovascular events only when saturated fat was being replaced with polyunsaturated fats.
In other words, reducing saturated fat had no effect on its own, but replacing it with polyunsaturated fats led to a 27% reduced risk of cardiovascular events (but not death, heart attacks or strokes).
They also found that the people who had the greatest reduction in serum total cholesterol were the most likely to experience a benefit.
This implies that changes in fat intake may be beneficial when they actually lead to a significant improvement in blood lipids.
These were the conclusions of the study:
“The findings of this updated review are suggestive of a small but potentially important reduction in cardiovascular risk on reduction of saturated fat intake. Replacing the energy from saturated fat with polyunsaturated fat appears to be a useful strategy, and replacement with carbohydrate appears less useful, but effects of replacement with monounsaturated fat were unclear due to inclusion of only one small trial.
This effect did not appear to alter by study duration, sex or baseline level of cardiovascular risk. Lifestyle advice to all those at risk of cardiovascular disease and to lower risk population groups should continue to include permanent reduction of dietary saturated fat and partial replacement by unsaturated fats. The ideal type of unsaturated fat is unclear.”
Cochrane reviews tend to be very conservative in their conclusions. Even though the data clearly suggests that reducing saturated fat is next to useless, they still claim in their conclusion that this is useful advice.
In this case, the study’s conclusions are not supported by the data.
It is hard to find any limitations to this study. It is just about as good as it gets when it comes to studies on nutrition.
The only major flaw is the misleading conclusion.
What Other Studies Say
The findings of this study are similar to a previous Cochrane review that was done in 2011 (3).
Despite the strange conclusion of the study authors, the data they derived from their review is another nail in the coffin of the diet-heart hypothesis.
This high-quality study shows that reducing saturated fat has no effect on heart attacks, strokes or the risk of dying from all causes.
However, there may be a modest cardiovascular benefit to replacing saturated fats with polyunsaturated fats, such as those found in fish, nuts and olive oil.
According to this current study, this is unlikely to prolong your life, but it may reduce your risk of experiencing a cardiovascular event slightly.
Importantly, despite saturated fat not being harmful in reasonable amounts, this does not mean that people should go out of their way to eat more of them.
This study only looked at people using reasonable amounts of saturated fat, and does not exonerate bulletproof coffee users – which are using much higher amounts of saturated fat than the participants in this review.
Real Life Applications
Saturated fats appear to be neither good, nor bad. They are just neutral.
However, we do know that there are fats out there that have actual benefits.
Emphasizing foods that contain healthy fats, such as fish, nuts, seeds and extra virgin olive oil, may lead to a net health benefit.
In other words, don’t avoid saturated fats, but still try to prioritize whole foods that contain fats that have clearly been shown to be healthy.